@chapter Filtering Introduction @c man begin FILTERING INTRODUCTION Filtering in FFmpeg is enabled through the libavfilter library. In libavfilter, a filter can have multiple inputs and multiple outputs. To illustrate the sorts of things that are possible, we consider the following filtergraph. @verbatim [main] input --> split ---------------------> overlay --> output | ^ |[tmp] [flip]| +-----> crop --> vflip -------+ @end verbatim This filtergraph splits the input stream in two streams, then sends one stream through the crop filter and the vflip filter, before merging it back with the other stream by overlaying it on top. You can use the following command to achieve this: @example ffmpeg -i INPUT -vf "split [main][tmp]; [tmp] crop=iw:ih/2:0:0, vflip [flip]; [main][flip] overlay=0:H/2" OUTPUT @end example The result will be that the top half of the video is mirrored onto the bottom half of the output video. Filters in the same linear chain are separated by commas, and distinct linear chains of filters are separated by semicolons. In our example, @var{crop,vflip} are in one linear chain, @var{split} and @var{overlay} are separately in another. The points where the linear chains join are labelled by names enclosed in square brackets. In the example, the split filter generates two outputs that are associated to the labels @var{[main]} and @var{[tmp]}. The stream sent to the second output of @var{split}, labelled as @var{[tmp]}, is processed through the @var{crop} filter, which crops away the lower half part of the video, and then vertically flipped. The @var{overlay} filter takes in input the first unchanged output of the split filter (which was labelled as @var{[main]}), and overlay on its lower half the output generated by the @var{crop,vflip} filterchain. Some filters take in input a list of parameters: they are specified after the filter name and an equal sign, and are separated from each other by a colon. There exist so-called @var{source filters} that do not have an audio/video input, and @var{sink filters} that will not have audio/video output. @c man end FILTERING INTRODUCTION @chapter graph2dot @c man begin GRAPH2DOT The @file{graph2dot} program included in the FFmpeg @file{tools} directory can be used to parse a filtergraph description and issue a corresponding textual representation in the dot language. Invoke the command: @example graph2dot -h @end example to see how to use @file{graph2dot}. You can then pass the dot description to the @file{dot} program (from the graphviz suite of programs) and obtain a graphical representation of the filtergraph. For example the sequence of commands: @example echo @var{GRAPH_DESCRIPTION} | \ tools/graph2dot -o graph.tmp && \ dot -Tpng graph.tmp -o graph.png && \ display graph.png @end example can be used to create and display an image representing the graph described by the @var{GRAPH_DESCRIPTION} string. Note that this string must be a complete self-contained graph, with its inputs and outputs explicitly defined. For example if your command line is of the form: @example ffmpeg -i infile -vf scale=640:360 outfile @end example your @var{GRAPH_DESCRIPTION} string will need to be of the form: @example nullsrc,scale=640:360,nullsink @end example you may also need to set the @var{nullsrc} parameters and add a @var{format} filter in order to simulate a specific input file. @c man end GRAPH2DOT @chapter Filtergraph description @c man begin FILTERGRAPH DESCRIPTION A filtergraph is a directed graph of connected filters. It can contain cycles, and there can be multiple links between a pair of filters. Each link has one input pad on one side connecting it to one filter from which it takes its input, and one output pad on the other side connecting it to one filter accepting its output. Each filter in a filtergraph is an instance of a filter class registered in the application, which defines the features and the number of input and output pads of the filter. A filter with no input pads is called a "source", and a filter with no output pads is called a "sink". @anchor{Filtergraph syntax} @section Filtergraph syntax A filtergraph has a textual representation, which is recognized by the @option{-filter}/@option{-vf}/@option{-af} and @option{-filter_complex} options in @command{ffmpeg} and @option{-vf}/@option{-af} in @command{ffplay}, and by the @code{avfilter_graph_parse_ptr()} function defined in @file{libavfilter/avfilter.h}. A filterchain consists of a sequence of connected filters, each one connected to the previous one in the sequence. A filterchain is represented by a list of ","-separated filter descriptions. A filtergraph consists of a sequence of filterchains. A sequence of filterchains is represented by a list of ";"-separated filterchain descriptions. A filter is represented by a string of the form: [@var{in_link_1}]...[@var{in_link_N}]@var{filter_name}@@@var{id}=@var{arguments}[@var{out_link_1}]...[@var{out_link_M}] @var{filter_name} is the name of the filter class of which the described filter is an instance of, and has to be the name of one of the filter classes registered in the program optionally followed by "@@@var{id}". The name of the filter class is optionally followed by a string "=@var{arguments}". @var{arguments} is a string which contains the parameters used to initialize the filter instance. It may have one of two forms: @itemize @item A ':'-separated list of @var{key=value} pairs. @item A ':'-separated list of @var{value}. In this case, the keys are assumed to be the option names in the order they are declared. E.g. the @code{fade} filter declares three options in this order -- @option{type}, @option{start_frame} and @option{nb_frames}. Then the parameter list @var{in:0:30} means that the value @var{in} is assigned to the option @option{type}, @var{0} to @option{start_frame} and @var{30} to @option{nb_frames}. @item A ':'-separated list of mixed direct @var{value} and long @var{key=value} pairs. The direct @var{value} must precede the @var{key=value} pairs, and follow the same constraints order of the previous point. The following @var{key=value} pairs can be set in any preferred order. @end itemize If the option value itself is a list of items (e.g. the @code{format} filter takes a list of pixel formats), the items in the list are usually separated by @samp{|}. The list of arguments can be quoted using the character @samp{'} as initial and ending mark, and the character @samp{\} for escaping the characters within the quoted text; otherwise the argument string is considered terminated when the next special character (belonging to the set @samp{[]=;,}) is encountered. The name and arguments of the filter are optionally preceded and followed by a list of link labels. A link label allows one to name a link and associate it to a filter output or input pad. The preceding labels @var{in_link_1} ... @var{in_link_N}, are associated to the filter input pads, the following labels @var{out_link_1} ... @var{out_link_M}, are associated to the output pads. When two link labels with the same name are found in the filtergraph, a link between the corresponding input and output pad is created. If an output pad is not labelled, it is linked by default to the first unlabelled input pad of the next filter in the filterchain. For example in the filterchain @example nullsrc, split[L1], [L2]overlay, nullsink @end example the split filter instance has two output pads, and the overlay filter instance two input pads. The first output pad of split is labelled "L1", the first input pad of overlay is labelled "L2", and the second output pad of split is linked to the second input pad of overlay, which are both unlabelled. In a filter description, if the input label of the first filter is not specified, "in" is assumed; if the output label of the last filter is not specified, "out" is assumed. In a complete filterchain all the unlabelled filter input and output pads must be connected. A filtergraph is considered valid if all the filter input and output pads of all the filterchains are connected. Libavfilter will automatically insert @ref{scale} filters where format conversion is required. It is possible to specify swscale flags for those automatically inserted scalers by prepending @code{sws_flags=@var{flags};} to the filtergraph description. Here is a BNF description of the filtergraph syntax: @example @var{NAME} ::= sequence of alphanumeric characters and '_' @var{FILTER_NAME} ::= @var{NAME}["@@"@var{NAME}] @var{LINKLABEL} ::= "[" @var{NAME} "]" @var{LINKLABELS} ::= @var{LINKLABEL} [@var{LINKLABELS}] @var{FILTER_ARGUMENTS} ::= sequence of chars (possibly quoted) @var{FILTER} ::= [@var{LINKLABELS}] @var{FILTER_NAME} ["=" @var{FILTER_ARGUMENTS}] [@var{LINKLABELS}] @var{FILTERCHAIN} ::= @var{FILTER} [,@var{FILTERCHAIN}] @var{FILTERGRAPH} ::= [sws_flags=@var{flags};] @var{FILTERCHAIN} [;@var{FILTERGRAPH}] @end example @anchor{filtergraph escaping} @section Notes on filtergraph escaping Filtergraph description composition entails several levels of escaping. See @ref{quoting_and_escaping,,the "Quoting and escaping" section in the ffmpeg-utils(1) manual,ffmpeg-utils} for more information about the employed escaping procedure. A first level escaping affects the content of each filter option value, which may contain the special character @code{:} used to separate values, or one of the escaping characters @code{\'}. A second level escaping affects the whole filter description, which may contain the escaping characters @code{\'} or the special characters @code{[],;} used by the filtergraph description. Finally, when you specify a filtergraph on a shell commandline, you need to perform a third level escaping for the shell special characters contained within it. For example, consider the following string to be embedded in the @ref{drawtext} filter description @option{text} value: @example this is a 'string': may contain one, or more, special characters @end example This string contains the @code{'} special escaping character, and the @code{:} special character, so it needs to be escaped in this way: @example text=this is a \'string\'\: may contain one, or more, special characters @end example A second level of escaping is required when embedding the filter description in a filtergraph description, in order to escape all the filtergraph special characters. Thus the example above becomes: @example drawtext=text=this is a \\\'string\\\'\\: may contain one\, or more\, special characters @end example (note that in addition to the @code{\'} escaping special characters, also @code{,} needs to be escaped). Finally an additional level of escaping is needed when writing the filtergraph description in a shell command, which depends on the escaping rules of the adopted shell. For example, assuming that @code{\} is special and needs to be escaped with another @code{\}, the previous string will finally result in: @example -vf "drawtext=text=this is a \\\\\\'string\\\\\\'\\\\: may contain one\\, or more\\, special characters" @end example @chapter Timeline editing Some filters support a generic @option{enable} option. For the filters supporting timeline editing, this option can be set to an expression which is evaluated before sending a frame to the filter. If the evaluation is non-zero, the filter will be enabled, otherwise the frame will be sent unchanged to the next filter in the filtergraph. The expression accepts the following values: @table @samp @item t timestamp expressed in seconds, NAN if the input timestamp is unknown @item n sequential number of the input frame, starting from 0 @item pos the position in the file of the input frame, NAN if unknown @item w @item h width and height of the input frame if video @end table Additionally, these filters support an @option{enable} command that can be used to re-define the expression. Like any other filtering option, the @option{enable} option follows the same rules. For example, to enable a blur filter (@ref{smartblur}) from 10 seconds to 3 minutes, and a @ref{curves} filter starting at 3 seconds: @example smartblur = enable='between(t,10,3*60)', curves = enable='gte(t,3)' : preset=cross_process @end example See @code{ffmpeg -filters} to view which filters have timeline support. @c man end FILTERGRAPH DESCRIPTION @anchor{framesync} @chapter Options for filters with several inputs (framesync) @c man begin OPTIONS FOR FILTERS WITH SEVERAL INPUTS Some filters with several inputs support a common set of options. These options can only be set by name, not with the short notation. @table @option @item eof_action The action to take when EOF is encountered on the secondary input; it accepts one of the following values: @table @option @item repeat Repeat the last frame (the default). @item endall End both streams. @item pass Pass the main input through. @end table @item shortest If set to 1, force the output to terminate when the shortest input terminates. Default value is 0. @item repeatlast If set to 1, force the filter to extend the last frame of secondary streams until the end of the primary stream. A value of 0 disables this behavior. Default value is 1. @end table @c man end OPTIONS FOR FILTERS WITH SEVERAL INPUTS @chapter Audio Filters @c man begin AUDIO FILTERS When you configure your FFmpeg build, you can disable any of the existing filters using @code{--disable-filters}. The configure output will show the audio filters included in your build. Below is a description of the currently available audio filters. @section acompressor A compressor is mainly used to reduce the dynamic range of a signal. Especially modern music is mostly compressed at a high ratio to improve the overall loudness. It's done to get the highest attention of a listener, "fatten" the sound and bring more "power" to the track. If a signal is compressed too much it may sound dull or "dead" afterwards or it may start to "pump" (which could be a powerful effect but can also destroy a track completely). The right compression is the key to reach a professional sound and is the high art of mixing and mastering. Because of its complex settings it may take a long time to get the right feeling for this kind of effect. Compression is done by detecting the volume above a chosen level @code{threshold} and dividing it by the factor set with @code{ratio}. So if you set the threshold to -12dB and your signal reaches -6dB a ratio of 2:1 will result in a signal at -9dB. Because an exact manipulation of the signal would cause distortion of the waveform the reduction can be levelled over the time. This is done by setting "Attack" and "Release". @code{attack} determines how long the signal has to rise above the threshold before any reduction will occur and @code{release} sets the time the signal has to fall below the threshold to reduce the reduction again. Shorter signals than the chosen attack time will be left untouched. The overall reduction of the signal can be made up afterwards with the @code{makeup} setting. So compressing the peaks of a signal about 6dB and raising the makeup to this level results in a signal twice as loud than the source. To gain a softer entry in the compression the @code{knee} flattens the hard edge at the threshold in the range of the chosen decibels. The filter accepts the following options: @table @option @item level_in Set input gain. Default is 1. Range is between 0.015625 and 64. @item threshold If a signal of stream rises above this level it will affect the gain reduction. By default it is 0.125. Range is between 0.00097563 and 1. @item ratio Set a ratio by which the signal is reduced. 1:2 means that if the level rose 4dB above the threshold, it will be only 2dB above after the reduction. Default is 2. Range is between 1 and 20. @item attack Amount of milliseconds the signal has to rise above the threshold before gain reduction starts. Default is 20. Range is between 0.01 and 2000. @item release Amount of milliseconds the signal has to fall below the threshold before reduction is decreased again. Default is 250. Range is between 0.01 and 9000. @item makeup Set the amount by how much signal will be amplified after processing. Default is 1. Range is from 1 to 64. @item knee Curve the sharp knee around the threshold to enter gain reduction more softly. Default is 2.82843. Range is between 1 and 8. @item link Choose if the @code{average} level between all channels of input stream or the louder(@code{maximum}) channel of input stream affects the reduction. Default is @code{average}. @item detection Should the exact signal be taken in case of @code{peak} or an RMS one in case of @code{rms}. Default is @code{rms} which is mostly smoother. @item mix How much to use compressed signal in output. Default is 1. Range is between 0 and 1. @end table @section acontrast Simple audio dynamic range commpression/expansion filter. The filter accepts the following options: @table @option @item contrast Set contrast. Default is 33. Allowed range is between 0 and 100. @end table @section acopy Copy the input audio source unchanged to the output. This is mainly useful for testing purposes. @section acrossfade Apply cross fade from one input audio stream to another input audio stream. The cross fade is applied for specified duration near the end of first stream. The filter accepts the following options: @table @option @item nb_samples, ns Specify the number of samples for which the cross fade effect has to last. At the end of the cross fade effect the first input audio will be completely silent. Default is 44100. @item duration, d Specify the duration of the cross fade effect. See @ref{time duration syntax,,the Time duration section in the ffmpeg-utils(1) manual,ffmpeg-utils} for the accepted syntax. By default the duration is determined by @var{nb_samples}. If set this option is used instead of @var{nb_samples}. @item overlap, o Should first stream end overlap with second stream start. Default is enabled. @item curve1 Set curve for cross fade transition for first stream. @item curve2 Set curve for cross fade transition for second stream. For description of available curve types see @ref{afade} filter description. @end table @subsection Examples @itemize @item Cross fade from one input to another: @example ffmpeg -i first.flac -i second.flac -filter_complex acrossfade=d=10:c1=exp:c2=exp output.flac @end example @item Cross fade from one input to another but without overlapping: @example ffmpeg -i first.flac -i second.flac -filter_complex acrossfade=d=10:o=0:c1=exp:c2=exp output.flac @end example @end itemize @section acrusher Reduce audio bit resolution. This filter is bit crusher with enhanced functionality. A bit crusher is used to audibly reduce number of bits an audio signal is sampled with. This doesn't change the bit depth at all, it just produces the effect. Material reduced in bit depth sounds more harsh and "digital". This filter is able to even round to continuous values instead of discrete bit depths. Additionally it has a D/C offset which results in different crushing of the lower and the upper half of the signal. An Anti-Aliasing setting is able to produce "softer" crushing sounds. Another feature of this filter is the logarithmic mode. This setting switches from linear distances between bits to logarithmic ones. The result is a much more "natural" sounding crusher which doesn't gate low signals for example. The human ear has a logarithmic perception, so this kind of crushing is much more pleasant. Logarithmic crushing is also able to get anti-aliased. The filter accepts the following options: @table @option @item level_in Set level in. @item level_out Set level out. @item bits Set bit reduction. @item mix Set mixing amount. @item mode Can be linear: @code{lin} or logarithmic: @code{log}. @item dc Set DC. @item aa Set anti-aliasing. @item samples Set sample reduction. @item lfo Enable LFO. By default disabled. @item lforange Set LFO range. @item lforate Set LFO rate. @end table @section adelay Delay one or more audio channels. Samples in delayed channel are filled with silence. The filter accepts the following option: @table @option @item delays Set list of delays in milliseconds for each channel separated by '|'. Unused delays will be silently ignored. If number of given delays is smaller than number of channels all remaining channels will not be delayed. If you want to delay exact number of samples, append 'S' to number. @end table @subsection Examples @itemize @item Delay first channel by 1.5 seconds, the third channel by 0.5 seconds and leave the second channel (and any other channels that may be present) unchanged. @example adelay=1500|0|500 @end example @item Delay second channel by 500 samples, the third channel by 700 samples and leave the first channel (and any other channels that may be present) unchanged. @example adelay=0|500S|700S @end example @end itemize @section aecho Apply echoing to the input audio. Echoes are reflected sound and can occur naturally amongst mountains (and sometimes large buildings) when talking or shouting; digital echo effects emulate this behaviour and are often used to help fill out the sound of a single instrument or vocal. The time difference between the original signal and the reflection is the @code{delay}, and the loudness of the reflected signal is the @code{decay}. Multiple echoes can have different delays and decays. A description of the accepted parameters follows. @table @option @item in_gain Set input gain of reflected signal. Default is @code{0.6}. @item out_gain Set output gain of reflected signal. Default is @code{0.3}. @item delays Set list of time intervals in milliseconds between original signal and reflections separated by '|'. Allowed range for each @code{delay} is @code{(0 - 90000.0]}. Default is @code{1000}. @item decays Set list of loudness of reflected signals separated by '|'. Allowed range for each @code{decay} is @code{(0 - 1.0]}. Default is @code{0.5}. @end table @subsection Examples @itemize @item Make it sound as if there are twice as many instruments as are actually playing: @example aecho=0.8:0.88:60:0.4 @end example @item If delay is very short, then it sound like a (metallic) robot playing music: @example aecho=0.8:0.88:6:0.4 @end example @item A longer delay will sound like an open air concert in the mountains: @example aecho=0.8:0.9:1000:0.3 @end example @item Same as above but with one more mountain: @example aecho=0.8:0.9:1000|1800:0.3|0.25 @end example @end itemize @section aemphasis Audio emphasis filter creates or restores material directly taken from LPs or emphased CDs with different filter curves. E.g. to store music on vinyl the signal has to be altered by a filter first to even out the disadvantages of this recording medium. Once the material is played back the inverse filter has to be applied to restore the distortion of the frequency response. The filter accepts the following options: @table @option @item level_in Set input gain. @item level_out Set output gain. @item mode Set filter mode. For restoring material use @code{reproduction} mode, otherwise use @code{production} mode. Default is @code{reproduction} mode. @item type Set filter type. Selects medium. Can be one of the following: @table @option @item col select Columbia. @item emi select EMI. @item bsi select BSI (78RPM). @item riaa select RIAA. @item cd select Compact Disc (CD). @item 50fm select 50µs (FM). @item 75fm select 75µs (FM). @item 50kf select 50µs (FM-KF). @item 75kf select 75µs (FM-KF). @end table @end table @section aeval Modify an audio signal according to the specified expressions. This filter accepts one or more expressions (one for each channel), which are evaluated and used to modify a corresponding audio signal. It accepts the following parameters: @table @option @item exprs Set the '|'-separated expressions list for each separate channel. If the number of input channels is greater than the number of expressions, the last specified expression is used for the remaining output channels. @item channel_layout, c Set output channel layout. If not specified, the channel layout is specified by the number of expressions. If set to @samp{same}, it will use by default the same input channel layout. @end table Each expression in @var{exprs} can contain the following constants and functions: @table @option @item ch channel number of the current expression @item n number of the evaluated sample, starting from 0 @item s sample rate @item t time of the evaluated sample expressed in seconds @item nb_in_channels @item nb_out_channels input and output number of channels @item val(CH) the value of input channel with number @var{CH} @end table Note: this filter is slow. For faster processing you should use a dedicated filter. @subsection Examples @itemize @item Half volume: @example aeval=val(ch)/2:c=same @end example @item Invert phase of the second channel: @example aeval=val(0)|-val(1) @end example @end itemize @anchor{afade} @section afade Apply fade-in/out effect to input audio. A description of the accepted parameters follows. @table @option @item type, t Specify the effect type, can be either @code{in} for fade-in, or @code{out} for a fade-out effect. Default is @code{in}. @item start_sample, ss Specify the number of the start sample for starting to apply the fade effect. Default is 0. @item nb_samples, ns Specify the number of samples for which the fade effect has to last. At the end of the fade-in effect the output audio will have the same volume as the input audio, at the end of the fade-out transition the output audio will be silence. Default is 44100. @item start_time, st Specify the start time of the fade effect. Default is 0. The value must be specified as a time duration; see @ref{time duration syntax,,the Time duration section in the ffmpeg-utils(1) manual,ffmpeg-utils} for the accepted syntax. If set this option is used instead of @var{start_sample}. @item duration, d Specify the duration of the fade effect. See @ref{time duration syntax,,the Time duration section in the ffmpeg-utils(1) manual,ffmpeg-utils} for the accepted syntax. At the end of the fade-in effect the output audio will have the same volume as the input audio, at the end of the fade-out transition the output audio will be silence. By default the duration is determined by @var{nb_samples}. If set this option is used instead of @var{nb_samples}. @item curve Set curve for fade transition. It accepts the following values: @table @option @item tri select triangular, linear slope (default) @item qsin select quarter of sine wave @item hsin select half of sine wave @item esin select exponential sine wave @item log select logarithmic @item ipar select inverted parabola @item qua select quadratic @item cub select cubic @item squ select square root @item cbr select cubic root @item par select parabola @item exp select exponential @item iqsin select inverted quarter of sine wave @item ihsin select inverted half of sine wave @item dese select double-exponential seat @item desi select double-exponential sigmoid @end table @end table @subsection Examples @itemize @item Fade in first 15 seconds of audio: @example afade=t=in:ss=0:d=15 @end example @item Fade out last 25 seconds of a 900 seconds audio: @example afade=t=out:st=875:d=25 @end example @end itemize @section afftfilt Apply arbitrary expressions to samples in frequency domain. @table @option @item real Set frequency domain real expression for each separate channel separated by '|'. Default is "1". If the number of input channels is greater than the number of expressions, the last specified expression is used for the remaining output channels. @item imag Set frequency domain imaginary expression for each separate channel separated by '|'. If not set, @var{real} option is used. Each expression in @var{real} and @var{imag} can contain the following constants: @table @option @item sr sample rate @item b current frequency bin number @item nb number of available bins @item ch channel number of the current expression @item chs number of channels @item pts current frame pts @end table @item win_size Set window size. It accepts the following values: @table @samp @item w16 @item w32 @item w64 @item w128 @item w256 @item w512 @item w1024 @item w2048 @item w4096 @item w8192 @item w16384 @item w32768 @item w65536 @end table Default is @code{w4096} @item win_func Set window function. Default is @code{hann}. @item overlap Set window overlap. If set to 1, the recommended overlap for selected window function will be picked. Default is @code{0.75}. @end table @subsection Examples @itemize @item Leave almost only low frequencies in audio: @example afftfilt="1-clip((b/nb)*b,0,1)" @end example @end itemize @anchor{afir} @section afir Apply an arbitrary Frequency Impulse Response filter. This filter is designed for applying long FIR filters, up to 30 seconds long. It can be used as component for digital crossover filters, room equalization, cross talk cancellation, wavefield synthesis, auralization, ambiophonics and ambisonics. This filter uses second stream as FIR coefficients. If second stream holds single channel, it will be used for all input channels in first stream, otherwise number of channels in second stream must be same as number of channels in first stream. It accepts the following parameters: @table @option @item dry Set dry gain. This sets input gain. @item wet Set wet gain. This sets final output gain. @item length Set Impulse Response filter length. Default is 1, which means whole IR is processed. @item again Enable applying gain measured from power of IR. @end table @subsection Examples @itemize @item Apply reverb to stream using mono IR file as second input, complete command using ffmpeg: @example ffmpeg -i input.wav -i middle_tunnel_1way_mono.wav -lavfi afir output.wav @end example @end itemize @anchor{aformat} @section aformat Set output format constraints for the input audio. The framework will negotiate the most appropriate format to minimize conversions. It accepts the following parameters: @table @option @item sample_fmts A '|'-separated list of requested sample formats. @item sample_rates A '|'-separated list of requested sample rates. @item channel_layouts A '|'-separated list of requested channel layouts. See @ref{channel layout syntax,,the Channel Layout section in the ffmpeg-utils(1) manual,ffmpeg-utils} for the required syntax. @end table If a parameter is omitted, all values are allowed. Force the output to either unsigned 8-bit or signed 16-bit stereo @example aformat=sample_fmts=u8|s16:channel_layouts=stereo @end example @section agate A gate is mainly used to reduce lower parts of a signal. This kind of signal processing reduces disturbing noise between useful signals. Gating is done by detecting the volume below a chosen level @var{threshold} and dividing it by the factor set with @var{ratio}. The bottom of the noise floor is set via @var{range}. Because an exact manipulation of the signal would cause distortion of the waveform the reduction can be levelled over time. This is done by setting @var{attack} and @var{release}. @var{attack} determines how long the signal has to fall below the threshold before any reduction will occur and @var{release} sets the time the signal has to rise above the threshold to reduce the reduction again. Shorter signals than the chosen attack time will be left untouched. @table @option @item level_in Set input level before filtering. Default is 1. Allowed range is from 0.015625 to 64. @item range Set the level of gain reduction when the signal is below the threshold. Default is 0.06125. Allowed range is from 0 to 1. @item threshold If a signal rises above this level the gain reduction is released. Default is 0.125. Allowed range is from 0 to 1. @item ratio Set a ratio by which the signal is reduced. Default is 2. Allowed range is from 1 to 9000. @item attack Amount of milliseconds the signal has to rise above the threshold before gain reduction stops. Default is 20 milliseconds. Allowed range is from 0.01 to 9000. @item release Amount of milliseconds the signal has to fall below the threshold before the reduction is increased again. Default is 250 milliseconds. Allowed range is from 0.01 to 9000. @item makeup Set amount of amplification of signal after processing. Default is 1. Allowed range is from 1 to 64. @item knee Curve the sharp knee around the threshold to enter gain reduction more softly. Default is 2.828427125. Allowed range is from 1 to 8. @item detection Choose if exact signal should be taken for detection or an RMS like one. Default is @code{rms}. Can be @code{peak} or @code{rms}. @item link Choose if the average level between all channels or the louder channel affects the reduction. Default is @code{average}. Can be @code{average} or @code{maximum}. @end table @section aiir Apply an arbitrary Infinite Impulse Response filter. It accepts the following parameters: @table @option @item z Set numerator/zeros coefficients. @item p Set denominator/poles coefficients. @item k Set channels gains. @item dry_gain Set input gain. @item wet_gain Set output gain. @item f Set coefficients format. @table @samp @item tf transfer function @item zp Z-plane zeros/poles, cartesian (default) @item pr Z-plane zeros/poles, polar radians @item pd Z-plane zeros/poles, polar degrees @end table @item r Set kind of processing. Can be @code{d} - direct or @code{s} - serial cascading. Defauls is @code{s}. @item e Set filtering precision. @table @samp @item dbl double-precision floating-point (default) @item flt single-precision floating-point @item i32 32-bit integers @item i16 16-bit integers @end table @end table Coefficients in @code{tf} format are separated by spaces and are in ascending order. Coefficients in @code{zp} format are separated by spaces and order of coefficients doesn't matter. Coefficients in @code{zp} format are complex numbers with @var{i} imaginary unit. Different coefficients and gains can be provided for every channel, in such case use '|' to separate coefficients or gains. Last provided coefficients will be used for all remaining channels. @subsection Examples @itemize @item Apply 2 pole elliptic notch at arround 5000Hz for 48000 Hz sample rate: @example aiir=k=1:z=7.957584807809675810E-1 -2.575128568908332300 3.674839853930788710 -2.57512875289799137 7.957586296317130880E-1:p=1 -2.86950072432325953 3.63022088054647218 -2.28075678147272232 6.361362326477423500E-1:f=tf:r=d @end example @item Same as above but in @code{zp} format: @example aiir=k=0.79575848078096756:z=0.80918701+0.58773007i 0.80918701-0.58773007i 0.80884700+0.58784055i 0.80884700-0.58784055i:p=0.63892345+0.59951235i 0.63892345-0.59951235i 0.79582691+0.44198673i 0.79582691-0.44198673i:f=zp:r=s @end example @end itemize @section alimiter The limiter prevents an input signal from rising over a desired threshold. This limiter uses lookahead technology to prevent your signal from distorting. It means that there is a small delay after the signal is processed. Keep in mind that the delay it produces is the attack time you set. The filter accepts the following options: @table @option @item level_in Set input gain. Default is 1. @item level_out Set output gain. Default is 1. @item limit Don't let signals above this level pass the limiter. Default is 1. @item attack The limiter will reach its attenuation level in this amount of time in milliseconds. Default is 5 milliseconds. @item release Come back from limiting to attenuation 1.0 in this amount of milliseconds. Default is 50 milliseconds. @item asc When gain reduction is always needed ASC takes care of releasing to an average reduction level rather than reaching a reduction of 0 in the release time. @item asc_level Select how much the release time is affected by ASC, 0 means nearly no changes in release time while 1 produces higher release times. @item level Auto level output signal. Default is enabled. This normalizes audio back to 0dB if enabled. @end table Depending on picked setting it is recommended to upsample input 2x or 4x times with @ref{aresample} before applying this filter. @section allpass Apply a two-pole all-pass filter with central frequency (in Hz) @var{frequency}, and filter-width @var{width}. An all-pass filter changes the audio's frequency to phase relationship without changing its frequency to amplitude relationship. The filter accepts the following options: @table @option @item frequency, f Set frequency in Hz. @item width_type, t Set method to specify band-width of filter. @table @option @item h Hz @item q Q-Factor @item o octave @item s slope @item k kHz @end table @item width, w Specify the band-width of a filter in width_type units. @item channels, c Specify which channels to filter, by default all available are filtered. @end table @subsection Commands This filter supports the following commands: @table @option @item frequency, f Change allpass frequency. Syntax for the command is : "@var{frequency}" @item width_type, t Change allpass width_type. Syntax for the command is : "@var{width_type}" @item width, w Change allpass width. Syntax for the command is : "@var{width}" @end table @section aloop Loop audio samples. The filter accepts the following options: @table @option @item loop Set the number of loops. Setting this value to -1 will result in infinite loops. Default is 0. @item size Set maximal number of samples. Default is 0. @item start Set first sample of loop. Default is 0. @end table @anchor{amerge} @section amerge Merge two or more audio streams into a single multi-channel stream. The filter accepts the following options: @table @option @item inputs Set the number of inputs. Default is 2. @end table If the channel layouts of the inputs are disjoint, and therefore compatible, the channel layout of the output will be set accordingly and the channels will be reordered as necessary. If the channel layouts of the inputs are not disjoint, the output will have all the channels of the first input then all the channels of the second input, in that order, and the channel layout of the output will be the default value corresponding to the total number of channels. For example, if the first input is in 2.1 (FL+FR+LF) and the second input is FC+BL+BR, then the output will be in 5.1, with the channels in the following order: a1, a2, b1, a3, b2, b3 (a1 is the first channel of the first input, b1 is the first channel of the second input). On the other hand, if both input are in stereo, the output channels will be in the default order: a1, a2, b1, b2, and the channel layout will be arbitrarily set to 4.0, which may or may not be the expected value. All inputs must have the same sample rate, and format. If inputs do not have the same duration, the output will stop with the shortest. @subsection Examples @itemize @item Merge two mono files into a stereo stream: @example amovie=left.wav [l] ; amovie=right.mp3 [r] ; [l] [r] amerge @end example @item Multiple merges assuming 1 video stream and 6 audio streams in @file{input.mkv}: @example ffmpeg -i input.mkv -filter_complex "[0:1][0:2][0:3][0:4][0:5][0:6] amerge=inputs=6" -c:a pcm_s16le output.mkv @end example @end itemize @section amix Mixes multiple audio inputs into a single output. Note that this filter only supports float samples (the @var{amerge} and @var{pan} audio filters support many formats). If the @var{amix} input has integer samples then @ref{aresample} will be automatically inserted to perform the conversion to float samples. For example @example ffmpeg -i INPUT1 -i INPUT2 -i INPUT3 -filter_complex amix=inputs=3:duration=first:dropout_transition=3 OUTPUT @end example will mix 3 input audio streams to a single output with the same duration as the first input and a dropout transition time of 3 seconds. It accepts the following parameters: @table @option @item inputs The number of inputs. If unspecified, it defaults to 2. @item duration How to determine the end-of-stream. @table @option @item longest The duration of the longest input. (default) @item shortest The duration of the shortest input. @item first The duration of the first input. @end table @item dropout_transition The transition time, in seconds, for volume renormalization when an input stream ends. The default value is 2 seconds. @item weights Specify weight of each input audio stream as sequence. Each weight is separated by space. By default all inputs have same weight. @end table @section anequalizer High-order parametric multiband equalizer for each channel. It accepts the following parameters: @table @option @item params This option string is in format: "c@var{chn} f=@var{cf} w=@var{w} g=@var{g} t=@var{f} | ..." Each equalizer band is separated by '|'. @table @option @item chn Set channel number to which equalization will be applied. If input doesn't have that channel the entry is ignored. @item f Set central frequency for band. If input doesn't have that frequency the entry is ignored. @item w Set band width in hertz. @item g Set band gain in dB. @item t Set filter type for band, optional, can be: @table @samp @item 0 Butterworth, this is default. @item 1 Chebyshev type 1. @item 2 Chebyshev type 2. @end table @end table @item curves With this option activated frequency response of anequalizer is displayed in video stream. @item size Set video stream size. Only useful if curves option is activated. @item mgain Set max gain that will be displayed. Only useful if curves option is activated. Setting this to a reasonable value makes it possible to display gain which is derived from neighbour bands which are too close to each other and thus produce higher gain when both are activated. @item fscale Set frequency scale used to draw frequency response in video output. Can be linear or logarithmic. Default is logarithmic. @item colors Set color for each channel curve which is going to be displayed in video stream. This is list of color names separated by space or by '|'. Unrecognised or missing colors will be replaced by white color. @end table @subsection Examples @itemize @item Lower gain by 10 of central frequency 200Hz and width 100 Hz for first 2 channels using Chebyshev type 1 filter: @example anequalizer=c0 f=200 w=100 g=-10 t=1|c1 f=200 w=100 g=-10 t=1 @end example @end itemize @subsection Commands This filter supports the following commands: @table @option @item change Alter existing filter parameters. Syntax for the commands is : "@var{fN}|f=@var{freq}|w=@var{width}|g=@var{gain}" @var{fN} is existing filter number, starting from 0, if no such filter is available error is returned. @var{freq} set new frequency parameter. @var{width} set new width parameter in herz. @var{gain} set new gain parameter in dB. Full filter invocation with asendcmd may look like this: asendcmd=c='4.0 anequalizer change 0|f=200|w=50|g=1',anequalizer=... @end table @section anull Pass the audio source unchanged to the output. @section apad Pad the end of an audio stream with silence. This can be used together with @command{ffmpeg} @option{-shortest} to extend audio streams to the same length as the video stream. A description of the accepted options follows. @table @option @item packet_size Set silence packet size. Default value is 4096. @item pad_len Set the number of samples of silence to add to the end. After the value is reached, the stream is terminated. This option is mutually exclusive with @option{whole_len}. @item whole_len Set the minimum total number of samples in the output audio stream. If the value is longer than the input audio length, silence is added to the end, until the value is reached. This option is mutually exclusive with @option{pad_len}. @end table If neither the @option{pad_len} nor the @option{whole_len} option is set, the filter will add silence to the end of the input stream indefinitely. @subsection Examples @itemize @item Add 1024 samples of silence to the end of the input: @example apad=pad_len=1024 @end example @item Make sure the audio output will contain at least 10000 samples, pad the input with silence if required: @example apad=whole_len=10000 @end example @item Use @command{ffmpeg} to pad the audio input with silence, so that the video stream will always result the shortest and will be converted until the end in the output file when using the @option{shortest} option: @example ffmpeg -i VIDEO -i AUDIO -filter_complex "[1:0]apad" -shortest OUTPUT @end example @end itemize @section aphaser Add a phasing effect to the input audio. A phaser filter creates series of peaks and troughs in the frequency spectrum. The position of the peaks and troughs are modulated so that they vary over time, creating a sweeping effect. A description of the accepted parameters follows. @table @option @item in_gain Set input gain. Default is 0.4. @item out_gain Set output gain. Default is 0.74 @item delay Set delay in milliseconds. Default is 3.0. @item decay Set decay. Default is 0.4. @item speed Set modulation speed in Hz. Default is 0.5. @item type Set modulation type. Default is triangular. It accepts the following values: @table @samp @item triangular, t @item sinusoidal, s @end table @end table @section apulsator Audio pulsator is something between an autopanner and a tremolo. But it can produce funny stereo effects as well. Pulsator changes the volume of the left and right channel based on a LFO (low frequency oscillator) with different waveforms and shifted phases. This filter have the ability to define an offset between left and right channel. An offset of 0 means that both LFO shapes match each other. The left and right channel are altered equally - a conventional tremolo. An offset of 50% means that the shape of the right channel is exactly shifted in phase (or moved backwards about half of the frequency) - pulsator acts as an autopanner. At 1 both curves match again. Every setting in between moves the phase shift gapless between all stages and produces some "bypassing" sounds with sine and triangle waveforms. The more you set the offset near 1 (starting from the 0.5) the faster the signal passes from the left to the right speaker. The filter accepts the following options: @table @option @item level_in Set input gain. By default it is 1. Range is [0.015625 - 64]. @item level_out Set output gain. By default it is 1. Range is [0.015625 - 64]. @item mode Set waveform shape the LFO will use. Can be one of: sine, triangle, square, sawup or sawdown. Default is sine. @item amount Set modulation. Define how much of original signal is affected by the LFO. @item offset_l Set left channel offset. Default is 0. Allowed range is [0 - 1]. @item offset_r Set right channel offset. Default is 0.5. Allowed range is [0 - 1]. @item width Set pulse width. Default is 1. Allowed range is [0 - 2]. @item timing Set possible timing mode. Can be one of: bpm, ms or hz. Default is hz. @item bpm Set bpm. Default is 120. Allowed range is [30 - 300]. Only used if timing is set to bpm. @item ms Set ms. Default is 500. Allowed range is [10 - 2000]. Only used if timing is set to ms. @item hz Set frequency in Hz. Default is 2. Allowed range is [0.01 - 100]. Only used if timing is set to hz. @end table @anchor{aresample} @section aresample Resample the input audio to the specified parameters, using the libswresample library. If none are specified then the filter will automatically convert between its input and output. This filter is also able to stretch/squeeze the audio data to make it match the timestamps or to inject silence / cut out audio to make it match the timestamps, do a combination of both or do neither. The filter accepts the syntax [@var{sample_rate}:]@var{resampler_options}, where @var{sample_rate} expresses a sample rate and @var{resampler_options} is a list of @var{key}=@var{value} pairs, separated by ":". See the @ref{Resampler Options,,"Resampler Options" section in the ffmpeg-resampler(1) manual,ffmpeg-resampler} for the complete list of supported options. @subsection Examples @itemize @item Resample the input audio to 44100Hz: @example aresample=44100 @end example @item Stretch/squeeze samples to the given timestamps, with a maximum of 1000 samples per second compensation: @example aresample=async=1000 @end example @end itemize @section areverse Reverse an audio clip. Warning: This filter requires memory to buffer the entire clip, so trimming is suggested. @subsection Examples @itemize @item Take the first 5 seconds of a clip, and reverse it. @example atrim=end=5,areverse @end example @end itemize @section asetnsamples Set the number of samples per each output audio frame. The last output packet may contain a different number of samples, as the filter will flush all the remaining samples when the input audio signals its end. The filter accepts the following options: @table @option @item nb_out_samples, n Set the number of frames per each output audio frame. The number is intended as the number of samples @emph{per each channel}. Default value is 1024. @item pad, p If set to 1, the filter will pad the last audio frame with zeroes, so that the last frame will contain the same number of samples as the previous ones. Default value is 1. @end table For example, to set the number of per-frame samples to 1234 and disable padding for the last frame, use: @example asetnsamples=n=1234:p=0 @end example @section asetrate Set the sample rate without altering the PCM data. This will result in a change of speed and pitch. The filter accepts the following options: @table @option @item sample_rate, r Set the output sample rate. Default is 44100 Hz. @end table @section ashowinfo Show a line containing various information for each input audio frame. The input audio is not modified. The shown line contains a sequence of key/value pairs of the form @var{key}:@var{value}. The following values are shown in the output: @table @option @item n The (sequential) number of the input frame, starting from 0. @item pts The presentation timestamp of the input frame, in time base units; the time base depends on the filter input pad, and is usually 1/@var{sample_rate}. @item pts_time The presentation timestamp of the input frame in seconds. @item pos position of the frame in the input stream, -1 if this information in unavailable and/or meaningless (for example in case of synthetic audio) @item fmt The sample format. @item chlayout The channel layout. @item rate The sample rate for the audio frame. @item nb_samples The number of samples (per channel) in the frame. @item checksum The Adler-32 checksum (printed in hexadecimal) of the audio data. For planar audio, the data is treated as if all the planes were concatenated. @item plane_checksums A list of Adler-32 checksums for each data plane. @end table @anchor{astats} @section astats Display time domain statistical information about the audio channels. Statistics are calculated and displayed for each audio channel and, where applicable, an overall figure is also given. It accepts the following option: @table @option @item length Short window length in seconds, used for peak and trough RMS measurement. Default is @code{0.05} (50 milliseconds). Allowed range is @code{[0.1 - 10]}. @item metadata Set metadata injection. All the metadata keys are prefixed with @code{lavfi.astats.X}, where @code{X} is channel number starting from 1 or string @code{Overall}. Default is disabled. Available keys for each channel are: DC_offset Min_level Max_level Min_difference Max_difference Mean_difference RMS_difference Peak_level RMS_peak RMS_trough Crest_factor Flat_factor Peak_count Bit_depth Dynamic_range and for Overall: DC_offset Min_level Max_level Min_difference Max_difference Mean_difference RMS_difference Peak_level RMS_level RMS_peak RMS_trough Flat_factor Peak_count Bit_depth Number_of_samples For example full key look like this @code{lavfi.astats.1.DC_offset} or this @code{lavfi.astats.Overall.Peak_count}. For description what each key means read below. @item reset Set number of frame after which stats are going to be recalculated. Default is disabled. @end table A description of each shown parameter follows: @table @option @item DC offset Mean amplitude displacement from zero. @item Min level Minimal sample level. @item Max level Maximal sample level. @item Min difference Minimal difference between two consecutive samples. @item Max difference Maximal difference between two consecutive samples. @item Mean difference Mean difference between two consecutive samples. The average of each difference between two consecutive samples. @item RMS difference Root Mean Square difference between two consecutive samples. @item Peak level dB @item RMS level dB Standard peak and RMS level measured in dBFS. @item RMS peak dB @item RMS trough dB Peak and trough values for RMS level measured over a short window. @item Crest factor Standard ratio of peak to RMS level (note: not in dB). @item Flat factor Flatness (i.e. consecutive samples with the same value) of the signal at its peak levels (i.e. either @var{Min level} or @var{Max level}). @item Peak count Number of occasions (not the number of samples) that the signal attained either @var{Min level} or @var{Max level}. @item Bit depth Overall bit depth of audio. Number of bits used for each sample. @item Dynamic range Measured dynamic range of audio in dB. @end table @section atempo Adjust audio tempo. The filter accepts exactly one parameter, the audio tempo. If not specified then the filter will assume nominal 1.0 tempo. Tempo must be in the [0.5, 2.0] range. @subsection Examples @itemize @item Slow down audio to 80% tempo: @example atempo=0.8 @end example @item To speed up audio to 125% tempo: @example atempo=1.25 @end example @end itemize @section atrim Trim the input so that the output contains one continuous subpart of the input. It accepts the following parameters: @table @option @item start Timestamp (in seconds) of the start of the section to keep. I.e. the audio sample with the timestamp @var{start} will be the first sample in the output. @item end Specify time of the first audio sample that will be dropped, i.e. the audio sample immediately preceding the one with the timestamp @var{end} will be the last sample in the output. @item start_pts Same as @var{start}, except this option sets the start timestamp in samples instead of seconds. @item end_pts Same as @var{end}, except this option sets the end timestamp in samples instead of seconds. @item duration The maximum duration of the output in seconds. @item start_sample The number of the first sample that should be output. @item end_sample The number of the first sample that should be dropped. @end table @option{start}, @option{end}, and @option{duration} are expressed as time duration specifications; see @ref{time duration syntax,,the Time duration section in the ffmpeg-utils(1) manual,ffmpeg-utils}. Note that the first two sets of the start/end options and the @option{duration} option look at the frame timestamp, while the _sample options simply count the samples that pass through the filter. So start/end_pts and start/end_sample will give different results when the timestamps are wrong, inexact or do not start at zero. Also note that this filter does not modify the timestamps. If you wish to have the output timestamps start at zero, insert the asetpts filter after the atrim filter. If multiple start or end options are set, this filter tries to be greedy and keep all samples that match at least one of the specified constraints. To keep only the part that matches all the constraints at once, chain multiple atrim filters. The defaults are such that all the input is kept. So it is possible to set e.g. just the end values to keep everything before the specified time. Examples: @itemize @item Drop everything except the second minute of input: @example ffmpeg -i INPUT -af atrim=60:120 @end example @item Keep only the first 1000 samples: @example ffmpeg -i INPUT -af atrim=end_sample=1000 @end example @end itemize @section bandpass Apply a two-pole Butterworth band-pass filter with central frequency @var{frequency}, and (3dB-point) band-width width. The @var{csg} option selects a constant skirt gain (peak gain = Q) instead of the default: constant 0dB peak gain. The filter roll off at 6dB per octave (20dB per decade). The filter accepts the following options: @table @option @item frequency, f Set the filter's central frequency. Default is @code{3000}. @item csg Constant skirt gain if set to 1. Defaults to 0. @item width_type, t Set method to specify band-width of filter. @table @option @item h Hz @item q Q-Factor @item o octave @item s slope @item k kHz @end table @item width, w Specify the band-width of a filter in width_type units. @item channels, c Specify which channels to filter, by default all available are filtered. @end table @subsection Commands This filter supports the following commands: @table @option @item frequency, f Change bandpass frequency. Syntax for the command is : "@var{frequency}" @item width_type, t Change bandpass width_type. Syntax for the command is : "@var{width_type}" @item width, w Change bandpass width. Syntax for the command is : "@var{width}" @end table @section bandreject Apply a two-pole Butterworth band-reject filter with central frequency @var{frequency}, and (3dB-point) band-width @var{width}. The filter roll off at 6dB per octave (20dB per decade). The filter accepts the following options: @table @option @item frequency, f Set the filter's central frequency. Default is @code{3000}. @item width_type, t Set method to specify band-width of filter. @table @option @item h Hz @item q Q-Factor @item o octave @item s slope @item k kHz @end table @item width, w Specify the band-width of a filter in width_type units. @item channels, c Specify which channels to filter, by default all available are filtered. @end table @subsection Commands This filter supports the following commands: @table @option @item frequency, f Change bandreject frequency. Syntax for the command is : "@var{frequency}" @item width_type, t Change bandreject width_type. Syntax for the command is : "@var{width_type}" @item width, w Change bandreject width. Syntax for the command is : "@var{width}" @end table @section bass Boost or cut the bass (lower) frequencies of the audio using a two-pole shelving filter with a response similar to that of a standard hi-fi's tone-controls. This is also known as shelving equalisation (EQ). The filter accepts the following options: @table @option @item gain, g Give the gain at 0 Hz. Its useful range is about -20 (for a large cut) to +20 (for a large boost). Beware of clipping when using a positive gain. @item frequency, f Set the filter's central frequency and so can be used to extend or reduce the frequency range to be boosted or cut. The default value is @code{100} Hz. @item width_type, t Set method to specify band-width of filter. @table @option @item h Hz @item q Q-Factor @item o octave @item s slope @item k kHz @end table @item width, w Determine how steep is the filter's shelf transition. @item channels, c Specify which channels to filter, by default all available are filtered. @end table @subsection Commands This filter supports the following commands: @table @option @item frequency, f Change bass frequency. Syntax for the command is : "@var{frequency}" @item width_type, t Change bass width_type. Syntax for the command is : "@var{width_type}" @item width, w Change bass width. Syntax for the command is : "@var{width}" @item gain, g Change bass gain. Syntax for the command is : "@var{gain}" @end table @section biquad Apply a biquad IIR filter with the given coefficients. Where @var{b0}, @var{b1}, @var{b2} and @var{a0}, @var{a1}, @var{a2} are the numerator and denominator coefficients respectively. and @var{channels}, @var{c} specify which channels to filter, by default all available are filtered. @subsection Commands This filter supports the following commands: @table @option @item a0 @item a1 @item a2 @item b0 @item b1 @item b2 Change biquad parameter. Syntax for the command is : "@var{value}" @end table @section bs2b Bauer stereo to binaural transformation, which improves headphone listening of stereo audio records. To enable compilation of this filter you need to configure FFmpeg with @code{--enable-libbs2b}. It accepts the following parameters: @table @option @item profile Pre-defined crossfeed level. @table @option @item default Default level (fcut=700, feed=50). @item cmoy Chu Moy circuit (fcut=700, feed=60). @item jmeier Jan Meier circuit (fcut=650, feed=95). @end table @item fcut Cut frequency (in Hz). @item feed Feed level (in Hz). @end table @section channelmap Remap input channels to new locations. It accepts the following parameters: @table @option @item map Map channels from input to output. The argument is a '|'-separated list of mappings, each in the @code{@var{in_channel}-@var{out_channel}} or @var{in_channel} form. @var{in_channel} can be either the name of the input channel (e.g. FL for front left) or its index in the input channel layout. @var{out_channel} is the name of the output channel or its index in the output channel layout. If @var{out_channel} is not given then it is implicitly an index, starting with zero and increasing by one for each mapping. @item channel_layout The channel layout of the output stream. @end table If no mapping is present, the filter will implicitly map input channels to output channels, preserving indices. @subsection Examples @itemize @item For example, assuming a 5.1+downmix input MOV file, @example ffmpeg -i in.mov -filter 'channelmap=map=DL-FL|DR-FR' out.wav @end example will create an output WAV file tagged as stereo from the downmix channels of the input. @item To fix a 5.1 WAV improperly encoded in AAC's native channel order @example ffmpeg -i in.wav -filter 'channelmap=1|2|0|5|3|4:5.1' out.wav @end example @end itemize @section channelsplit Split each channel from an input audio stream into a separate output stream. It accepts the following parameters: @table @option @item channel_layout The channel layout of the input stream. The default is "stereo". @item channels A channel layout describing the channels to be extracted as separate output streams or "all" to extract each input channel as a separate stream. The default is "all". Choosing channels not present in channel layout in the input will result in an error. @end table @subsection Examples @itemize @item For example, assuming a stereo input MP3 file, @example ffmpeg -i in.mp3 -filter_complex channelsplit out.mkv @end example will create an output Matroska file with two audio streams, one containing only the left channel and the other the right channel. @item Split a 5.1 WAV file into per-channel files: @example ffmpeg -i in.wav -filter_complex 'channelsplit=channel_layout=5.1[FL][FR][FC][LFE][SL][SR]' -map '[FL]' front_left.wav -map '[FR]' front_right.wav -map '[FC]' front_center.wav -map '[LFE]' lfe.wav -map '[SL]' side_left.wav -map '[SR]' side_right.wav @end example @item Extract only LFE from a 5.1 WAV file: @example ffmpeg -i in.wav -filter_complex 'channelsplit=channel_layout=5.1:channels=LFE[LFE]' -map '[LFE]' lfe.wav @end example @end itemize @section chorus Add a chorus effect to the audio. Can make a single vocal sound like a chorus, but can also be applied to instrumentation. Chorus resembles an echo effect with a short delay, but whereas with echo the delay is constant, with chorus, it is varied using using sinusoidal or triangular modulation. The modulation depth defines the range the modulated delay is played before or after the delay. Hence the delayed sound will sound slower or faster, that is the delayed sound tuned around the original one, like in a chorus where some vocals are slightly off key. It accepts the following parameters: @table @option @item in_gain Set input gain. Default is 0.4. @item out_gain Set output gain. Default is 0.4. @item delays Set delays. A typical delay is around 40ms to 60ms. @item decays Set decays. @item speeds Set speeds. @item depths Set depths. @end table @subsection Examples @itemize @item A single delay: @example chorus=0.7:0.9:55:0.4:0.25:2 @end example @item Two delays: @example chorus=0.6:0.9:50|60:0.4|0.32:0.25|0.4:2|1.3 @end example @item Fuller sounding chorus with three delays: @example chorus=0.5:0.9:50|60|40:0.4|0.32|0.3:0.25|0.4|0.3:2|2.3|1.3 @end example @end itemize @section compand Compress or expand the audio's dynamic range. It accepts the following parameters: @table @option @item attacks @item decays A list of times in seconds for each channel over which the instantaneous level of the input signal is averaged to determine its volume. @var{attacks} refers to increase of volume and @var{decays} refers to decrease of volume. For most situations, the attack time (response to the audio getting louder) should be shorter than the decay time, because the human ear is more sensitive to sudden loud audio than sudden soft audio. A typical value for attack is 0.3 seconds and a typical value for decay is 0.8 seconds. If specified number of attacks & decays is lower than number of channels, the last set attack/decay will be used for all remaining channels. @item points A list of points for the transfer function, specified in dB relative to the maximum possible signal amplitude. Each key points list must be defined using the following syntax: @code{x0/y0|x1/y1|x2/y2|....} or @code{x0/y0 x1/y1 x2/y2 ....} The input values must be in strictly increasing order but the transfer function does not have to be monotonically rising. The point @code{0/0} is assumed but may be overridden (by @code{0/out-dBn}). Typical values for the transfer function are @code{-70/-70|-60/-20|1/0}. @item soft-knee Set the curve radius in dB for all joints. It defaults to 0.01. @item gain Set the additional gain in dB to be applied at all points on the transfer function. This allows for easy adjustment of the overall gain. It defaults to 0. @item volume Set an initial volume, in dB, to be assumed for each channel when filtering starts. This permits the user to supply a nominal level initially, so that, for example, a very large gain is not applied to initial signal levels before the companding has begun to operate. A typical value for audio which is initially quiet is -90 dB. It defaults to 0. @item delay Set a delay, in seconds. The input audio is analyzed immediately, but audio is delayed before being fed to the volume adjuster. Specifying a delay approximately equal to the attack/decay times allows the filter to effectively operate in predictive rather than reactive mode. It defaults to 0. @end table @subsection Examples @itemize @item Make music with both quiet and loud passages suitable for listening to in a noisy environment: @example compand=.3|.3:1|1:-90/-60|-60/-40|-40/-30|-20/-20:6:0:-90:0.2 @end example Another example for audio with whisper and explosion parts: @example compand=0|0:1|1:-90/-900|-70/-70|-30/-9|0/-3:6:0:0:0 @end example @item A noise gate for when the noise is at a lower level than the signal: @example compand=.1|.1:.2|.2:-900/-900|-50.1/-900|-50/-50:.01:0:-90:.1 @end example @item Here is another noise gate, this time for when the noise is at a higher level than the signal (making it, in some ways, similar to squelch): @example compand=.1|.1:.1|.1:-45.1/-45.1|-45/-900|0/-900:.01:45:-90:.1 @end example @item 2:1 compression starting at -6dB: @example compand=points=-80/-80|-6/-6|0/-3.8|20/3.5 @end example @item 2:1 compression starting at -9dB: @example compand=points=-80/-80|-9/-9|0/-5.3|20/2.9 @end example @item 2:1 compression starting at -12dB: @example compand=points=-80/-80|-12/-12|0/-6.8|20/1.9 @end example @item 2:1 compression starting at -18dB: @example compand=points=-80/-80|-18/-18|0/-9.8|20/0.7 @end example @item 3:1 compression starting at -15dB: @example compand=points=-80/-80|-15/-15|0/-10.8|20/-5.2 @end example @item Compressor/Gate: @example compand=points=-80/-105|-62/-80|-15.4/-15.4|0/-12|20/-7.6 @end example @item Expander: @example compand=attacks=0:points=-80/-169|-54/-80|-49.5/-64.6|-41.1/-41.1|-25.8/-15|-10.8/-4.5|0/0|20/8.3 @end example @item Hard limiter at -6dB: @example compand=attacks=0:points=-80/-80|-6/-6|20/-6 @end example @item Hard limiter at -12dB: @example compand=attacks=0:points=-80/-80|-12/-12|20/-12 @end example @item Hard noise gate at -35 dB: @example compand=attacks=0:points=-80/-115|-35.1/-80|-35/-35|20/20 @end example @item Soft limiter: @example compand=attacks=0:points=-80/-80|-12.4/-12.4|-6/-8|0/-6.8|20/-2.8 @end example @end itemize @section compensationdelay Compensation Delay Line is a metric based delay to compensate differing positions of microphones or speakers. For example, you have recorded guitar with two microphones placed in different location. Because the front of sound wave has fixed speed in normal conditions, the phasing of microphones can vary and depends on their location and interposition. The best sound mix can be achieved when these microphones are in phase (synchronized). Note that distance of ~30 cm between microphones makes one microphone to capture signal in antiphase to another microphone. That makes the final mix sounding moody. This filter helps to solve phasing problems by adding different delays to each microphone track and make them synchronized. The best result can be reached when you take one track as base and synchronize other tracks one by one with it. Remember that synchronization/delay tolerance depends on sample rate, too. Higher sample rates will give more tolerance. It accepts the following parameters: @table @option @item mm Set millimeters distance. This is compensation distance for fine tuning. Default is 0. @item cm Set cm distance. This is compensation distance for tightening distance setup. Default is 0. @item m Set meters distance. This is compensation distance for hard distance setup. Default is 0. @item dry Set dry amount. Amount of unprocessed (dry) signal. Default is 0. @item wet Set wet amount. Amount of processed (wet) signal. Default is 1. @item temp Set temperature degree in Celsius. This is the temperature of the environment. Default is 20. @end table @section crossfeed Apply headphone crossfeed filter. Crossfeed is the process of blending the left and right channels of stereo audio recording. It is mainly used to reduce extreme stereo separation of low frequencies. The intent is to produce more speaker like sound to the listener. The filter accepts the following options: @table @option @item strength Set strength of crossfeed. Default is 0.2. Allowed range is from 0 to 1. This sets gain of low shelf filter for side part of stereo image. Default is -6dB. Max allowed is -30db when strength is set to 1. @item range Set soundstage wideness. Default is 0.5. Allowed range is from 0 to 1. This sets cut off frequency of low shelf filter. Default is cut off near 1550 Hz. With range set to 1 cut off frequency is set to 2100 Hz. @item level_in Set input gain. Default is 0.9. @item level_out Set output gain. Default is 1. @end table @section crystalizer Simple algorithm to expand audio dynamic range. The filter accepts the following options: @table @option @item i Sets the intensity of effect (default: 2.0). Must be in range between 0.0 (unchanged sound) to 10.0 (maximum effect). @item c Enable clipping. By default is enabled. @end table @section dcshift Apply a DC shift to the audio. This can be useful to remove a DC offset (caused perhaps by a hardware problem in the recording chain) from the audio. The effect of a DC offset is reduced headroom and hence volume. The @ref{astats} filter can be used to determine if a signal has a DC offset. @table @option @item shift Set the DC shift, allowed range is [-1, 1]. It indicates the amount to shift the audio. @item limitergain Optional. It should have a value much less than 1 (e.g. 0.05 or 0.02) and is used to prevent clipping. @end table @section drmeter Measure audio dynamic range. DR values of 14 and higher is found in very dynamic material. DR of 8 to 13 is found in transition material. And anything less that 8 have very poor dynamics and is very compressed. The filter accepts the following options: @table @option @item length Set window length in seconds used to split audio into segments of equal length. Default is 3 seconds. @end table @section dynaudnorm Dynamic Audio Normalizer. This filter applies a certain amount of gain to the input audio in order to bring its peak magnitude to a target level (e.g. 0 dBFS). However, in contrast to more "simple" normalization algorithms, the Dynamic Audio Normalizer *dynamically* re-adjusts the gain factor to the input audio. This allows for applying extra gain to the "quiet" sections of the audio while avoiding distortions or clipping the "loud" sections. In other words: The Dynamic Audio Normalizer will "even out" the volume of quiet and loud sections, in the sense that the volume of each section is brought to the same target level. Note, however, that the Dynamic Audio Normalizer achieves this goal *without* applying "dynamic range compressing". It will retain 100% of the dynamic range *within* each section of the audio file. @table @option @item f Set the frame length in milliseconds. In range from 10 to 8000 milliseconds. Default is 500 milliseconds. The Dynamic Audio Normalizer processes the input audio in small chunks, referred to as frames. This is required, because a peak magnitude has no meaning for just a single sample value. Instead, we need to determine the peak magnitude for a contiguous sequence of sample values. While a "standard" normalizer would simply use the peak magnitude of the complete file, the Dynamic Audio Normalizer determines the peak magnitude individually for each frame. The length of a frame is specified in milliseconds. By default, the Dynamic Audio Normalizer uses a frame length of 500 milliseconds, which has been found to give good results with most files. Note that the exact frame length, in number of samples, will be determined automatically, based on the sampling rate of the individual input audio file. @item g Set the Gaussian filter window size. In range from 3 to 301, must be odd number. Default is 31. Probably the most important parameter of the Dynamic Audio Normalizer is the @code{window size} of the Gaussian smoothing filter. The filter's window size is specified in frames, centered around the current frame. For the sake of simplicity, this must be an odd number. Consequently, the default value of 31 takes into account the current frame, as well as the 15 preceding frames and the 15 subsequent frames. Using a larger window results in a stronger smoothing effect and thus in less gain variation, i.e. slower gain adaptation. Conversely, using a smaller window results in a weaker smoothing effect and thus in more gain variation, i.e. faster gain adaptation. In other words, the more you increase this value, the more the Dynamic Audio Normalizer will behave like a "traditional" normalization filter. On the contrary, the more you decrease this value, the more the Dynamic Audio Normalizer will behave like a dynamic range compressor. @item p Set the target peak value. This specifies the highest permissible magnitude level for the normalized audio input. This filter will try to approach the target peak magnitude as closely as possible, but at the same time it also makes sure that the normalized signal will never exceed the peak magnitude. A frame's maximum local gain factor is imposed directly by the target peak magnitude. The default value is 0.95 and thus leaves a headroom of 5%*. It is not recommended to go above this value. @item m Set the maximum gain factor. In range from 1.0 to 100.0. Default is 10.0. The Dynamic Audio Normalizer determines the maximum possible (local) gain factor for each input frame, i.e. the maximum gain factor that does not result in clipping or distortion. The maximum gain factor is determined by the frame's highest magnitude sample. However, the Dynamic Audio Normalizer additionally bounds the frame's maximum gain factor by a predetermined (global) maximum gain factor. This is done in order to avoid excessive gain factors in "silent" or almost silent frames. By default, the maximum gain factor is 10.0, For most inputs the default value should be sufficient and it usually is not recommended to increase this value. Though, for input with an extremely low overall volume level, it may be necessary to allow even higher gain factors. Note, however, that the Dynamic Audio Normalizer does not simply apply a "hard" threshold (i.e. cut off values above the threshold). Instead, a "sigmoid" threshold function will be applied. This way, the gain factors will smoothly approach the threshold value, but never exceed that value. @item r Set the target RMS. In range from 0.0 to 1.0. Default is 0.0 - disabled. By default, the Dynamic Audio Normalizer performs "peak" normalization. This means that the maximum local gain factor for each frame is defined (only) by the frame's highest magnitude sample. This way, the samples can be amplified as much as possible without exceeding the maximum signal level, i.e. without clipping. Optionally, however, the Dynamic Audio Normalizer can also take into account the frame's root mean square, abbreviated RMS. In electrical engineering, the RMS is commonly used to determine the power of a time-varying signal. It is therefore considered that the RMS is a better approximation of the "perceived loudness" than just looking at the signal's peak magnitude. Consequently, by adjusting all frames to a constant RMS value, a uniform "perceived loudness" can be established. If a target RMS value has been specified, a frame's local gain factor is defined as the factor that would result in exactly that RMS value. Note, however, that the maximum local gain factor is still restricted by the frame's highest magnitude sample, in order to prevent clipping. @item n Enable channels coupling. By default is enabled. By default, the Dynamic Audio Normalizer will amplify all channels by the same amount. This means the same gain factor will be applied to all channels, i.e. the maximum possible gain factor is determined by the "loudest" channel. However, in some recordings, it may happen that the volume of the different channels is uneven, e.g. one channel may be "quieter" than the other one(s). In this case, this option can be used to disable the channel coupling. This way, the gain factor will be determined independently for each channel, depending only on the individual channel's highest magnitude sample. This allows for harmonizing the volume of the different channels. @item c Enable DC bias correction. By default is disabled. An audio signal (in the time domain) is a sequence of sample values. In the Dynamic Audio Normalizer these sample values are represented in the -1.0 to 1.0 range, regardless of the original input format. Normally, the audio signal, or "waveform", should be centered around the zero point. That means if we calculate the mean value of all samples in a file, or in a single frame, then the result should be 0.0 or at least very close to that value. If, however, there is a significant deviation of the mean value from 0.0, in either positive or negative direction, this is referred to as a DC bias or DC offset. Since a DC bias is clearly undesirable, the Dynamic Audio Normalizer provides optional DC bias correction. With DC bias correction enabled, the Dynamic Audio Normalizer will determine the mean value, or "DC correction" offset, of each input frame and subtract that value from all of the frame's sample values which ensures those samples are centered around 0.0 again. Also, in order to avoid "gaps" at the frame boundaries, the DC correction offset values will be interpolated smoothly between neighbouring frames. @item b Enable alternative boundary mode. By default is disabled. The Dynamic Audio Normalizer takes into account a certain neighbourhood around each frame. This includes the preceding frames as well as the subsequent frames. However, for the "boundary" frames, located at the very beginning and at the very end of the audio file, not all neighbouring frames are available. In particular, for the first few frames in the audio file, the preceding frames are not known. And, similarly, for the last few frames in the audio file, the subsequent frames are not known. Thus, the question arises which gain factors should be assumed for the missing frames in the "boundary" region. The Dynamic Audio Normalizer implements two modes to deal with this situation. The default boundary mode assumes a gain factor of exactly 1.0 for the missing frames, resulting in a smooth "fade in" and "fade out" at the beginning and at the end of the input, respectively. @item s Set the compress factor. In range from 0.0 to 30.0. Default is 0.0. By default, the Dynamic Audio Normalizer does not apply "traditional" compression. This means that signal peaks will not be pruned and thus the full dynamic range will be retained within each local neighbourhood. However, in some cases it may be desirable to combine the Dynamic Audio Normalizer's normalization algorithm with a more "traditional" compression. For this purpose, the Dynamic Audio Normalizer provides an optional compression (thresholding) function. If (and only if) the compression feature is enabled, all input frames will be processed by a soft knee thresholding function prior to the actual normalization process. Put simply, the thresholding function is going to prune all samples whose magnitude exceeds a certain threshold value. However, the Dynamic Audio Normalizer does not simply apply a fixed threshold value. Instead, the threshold value will be adjusted for each individual frame. In general, smaller parameters result in stronger compression, and vice versa. Values below 3.0 are not recommended, because audible distortion may appear. @end table @section earwax Make audio easier to listen to on headphones. This filter adds `cues' to 44.1kHz stereo (i.e. audio CD format) audio so that when listened to on headphones the stereo image is moved from inside your head (standard for headphones) to outside and in front of the listener (standard for speakers). Ported from SoX. @section equalizer Apply a two-pole peaking equalisation (EQ) filter. With this filter, the signal-level at and around a selected frequency can be increased or decreased, whilst (unlike bandpass and bandreject filters) that at all other frequencies is unchanged. In order to produce complex equalisation curves, this filter can be given several times, each with a different central frequency. The filter accepts the following options: @table @option @item frequency, f Set the filter's central frequency in Hz. @item width_type, t Set method to specify band-width of filter. @table @option @item h Hz @item q Q-Factor @item o octave @item s slope @item k kHz @end table @item width, w Specify the band-width of a filter in width_type units. @item gain, g Set the required gain or attenuation in dB. Beware of clipping when using a positive gain. @item channels, c Specify which channels to filter, by default all available are filtered. @end table @subsection Examples @itemize @item Attenuate 10 dB at 1000 Hz, with a bandwidth of 200 Hz: @example equalizer=f=1000:t=h:width=200:g=-10 @end example @item Apply 2 dB gain at 1000 Hz with Q 1 and attenuate 5 dB at 100 Hz with Q 2: @example equalizer=f=1000:t=q:w=1:g=2,equalizer=f=100:t=q:w=2:g=-5 @end example @end itemize @subsection Commands This filter supports the following commands: @table @option @item frequency, f Change equalizer frequency. Syntax for the command is : "@var{frequency}" @item width_type, t Change equalizer width_type. Syntax for the command is : "@var{width_type}" @item width, w Change equalizer width. Syntax for the command is : "@var{width}" @item gain, g Change equalizer gain. Syntax for the command is : "@var{gain}" @end table @section extrastereo Linearly increases the difference between left and right channels which adds some sort of "live" effect to playback. The filter accepts the following options: @table @option @item m Sets the difference coefficient (default: 2.5). 0.0 means mono sound (average of both channels), with 1.0 sound will be unchanged, with -1.0 left and right channels will be swapped. @item c Enable clipping. By default is enabled. @end table @section firequalizer Apply FIR Equalization using arbitrary frequency response. The filter accepts the following option: @table @option @item gain Set gain curve equation (in dB). The expression can contain variables: @table @option @item f the evaluated frequency @item sr sample rate @item ch channel number, set to 0 when multichannels evaluation is disabled @item chid channel id, see libavutil/channel_layout.h, set to the first channel id when multichannels evaluation is disabled @item chs number of channels @item chlayout channel_layout, see libavutil/channel_layout.h @end table and functions: @table @option @item gain_interpolate(f) interpolate gain on frequency f based on gain_entry @item cubic_interpolate(f) same as gain_interpolate, but smoother @end table This option is also available as command. Default is @code{gain_interpolate(f)}. @item gain_entry Set gain entry for gain_interpolate function. The expression can contain functions: @table @option @item entry(f, g) store gain entry at frequency f with value g @end table This option is also available as command. @item delay Set filter delay in seconds. Higher value means more accurate. Default is @code{0.01}. @item accuracy Set filter accuracy in Hz. Lower value means more accurate. Default is @code{5}. @item wfunc Set window function. Acceptable values are: @table @option @item rectangular rectangular window, useful when gain curve is already smooth @item hann hann window (default) @item hamming hamming window @item blackman blackman window @item nuttall3 3-terms continuous 1st derivative nuttall window @item mnuttall3 minimum 3-terms discontinuous nuttall window @item nuttall 4-terms continuous 1st derivative nuttall window @item bnuttall minimum 4-terms discontinuous nuttall (blackman-nuttall) window @item bharris blackman-harris window @item tukey tukey window @end table @item fixed If enabled, use fixed number of audio samples. This improves speed when filtering with large delay. Default is disabled. @item multi Enable multichannels evaluation on gain. Default is disabled. @item zero_phase Enable zero phase mode by subtracting timestamp to compensate delay. Default is disabled. @item scale Set scale used by gain. Acceptable values are: @table @option @item linlin linear frequency, linear gain @item linlog linear frequency, logarithmic (in dB) gain (default) @item loglin logarithmic (in octave scale where 20 Hz is 0) frequency, linear gain @item loglog logarithmic frequency, logarithmic gain @end table @item dumpfile Set file for dumping, suitable for gnuplot. @item dumpscale Set scale for dumpfile. Acceptable values are same with scale option. Default is linlog. @item fft2 Enable 2-channel convolution using complex FFT. This improves speed significantly. Default is disabled. @item min_phase Enable minimum phase impulse response. Default is disabled. @end table @subsection Examples @itemize @item lowpass at 1000 Hz: @example firequalizer=gain='if(lt(f,1000), 0, -INF)' @end example @item lowpass at 1000 Hz with gain_entry: @example firequalizer=gain_entry='entry(1000,0); entry(1001, -INF)' @end example @item custom equalization: @example firequalizer=gain_entry='entry(100,0); entry(400, -4); entry(1000, -6); entry(2000, 0)' @end example @item higher delay with zero phase to compensate delay: @example firequalizer=delay=0.1:fixed=on:zero_phase=on @end example @item lowpass on left channel, highpass on right channel: @example firequalizer=gain='if(eq(chid,1), gain_interpolate(f), if(eq(chid,2), gain_interpolate(1e6+f), 0))' :gain_entry='entry(1000, 0); entry(1001,-INF); entry(1e6+1000,0)':multi=on @end example @end itemize @section flanger Apply a flanging effect to the audio. The filter accepts the following options: @table @option @item delay Set base delay in milliseconds. Range from 0 to 30. Default value is 0. @item depth Set added sweep delay in milliseconds. Range from 0 to 10. Default value is 2. @item regen Set percentage regeneration (delayed signal feedback). Range from -95 to 95. Default value is 0. @item width Set percentage of delayed signal mixed with original. Range from 0 to 100. Default value is 71. @item speed Set sweeps per second (Hz). Range from 0.1 to 10. Default value is 0.5. @item shape Set swept wave shape, can be @var{triangular} or @var{sinusoidal}. Default value is @var{sinusoidal}. @item phase Set swept wave percentage-shift for multi channel. Range from 0 to 100. Default value is 25. @item interp Set delay-line interpolation, @var{linear} or @var{quadratic}. Default is @var{linear}. @end table @section haas Apply Haas effect to audio. Note that this makes most sense to apply on mono signals. With this filter applied to mono signals it give some directionality and stretches its stereo image. The filter accepts the following options: @table @option @item level_in Set input level. By default is @var{1}, or 0dB @item level_out Set output level. By default is @var{1}, or 0dB. @item side_gain Set gain applied to side part of signal. By default is @var{1}. @item middle_source Set kind of middle source. Can be one of the following: @table @samp @item left Pick left channel. @item right Pick right channel. @item mid Pick middle part signal of stereo image. @item side Pick side part signal of stereo image. @end table @item middle_phase Change middle phase. By default is disabled. @item left_delay Set left channel delay. By default is @var{2.05} milliseconds. @item left_balance Set left channel balance. By default is @var{-1}. @item left_gain Set left channel gain. By default is @var{1}. @item left_phase Change left phase. By default is disabled. @item right_delay Set right channel delay. By defaults is @var{2.12} milliseconds. @item right_balance Set right channel balance. By default is @var{1}. @item right_gain Set right channel gain. By default is @var{1}. @item right_phase Change right phase. By default is enabled. @end table @section hdcd Decodes High Definition Compatible Digital (HDCD) data. A 16-bit PCM stream with embedded HDCD codes is expanded into a 20-bit PCM stream. The filter supports the Peak Extend and Low-level Gain Adjustment features of HDCD, and detects the Transient Filter flag. @example ffmpeg -i HDCD16.flac -af hdcd OUT24.flac @end example When using the filter with wav, note the default encoding for wav is 16-bit, so the resulting 20-bit stream will be truncated back to 16-bit. Use something like @command{-acodec pcm_s24le} after the filter to get 24-bit PCM output. @example ffmpeg -i HDCD16.wav -af hdcd OUT16.wav ffmpeg -i HDCD16.wav -af hdcd -c:a pcm_s24le OUT24.wav @end example The filter accepts the following options: @table @option @item disable_autoconvert Disable any automatic format conversion or resampling in the filter graph. @item process_stereo Process the stereo channels together. If target_gain does not match between channels, consider it invalid and use the last valid target_gain. @item cdt_ms Set the code detect timer period in ms. @item force_pe Always extend peaks above -3dBFS even if PE isn't signaled. @item analyze_mode Replace audio with a solid tone and adjust the amplitude to signal some specific aspect of the decoding process. The output file can be loaded in an audio editor alongside the original to aid analysis. @code{analyze_mode=pe:force_pe=true} can be used to see all samples above the PE level. Modes are: @table @samp @item 0, off Disabled @item 1, lle Gain adjustment level at each sample @item 2, pe Samples where peak extend occurs @item 3, cdt Samples where the code detect timer is active @item 4, tgm Samples where the target gain does not match between channels @end table @end table @section headphone Apply head-related transfer functions (HRTFs) to create virtual loudspeakers around the user for binaural listening via headphones. The HRIRs are provided via additional streams, for each channel one stereo input stream is needed. The filter accepts the following options: @table @option @item map Set mapping of input streams for convolution. The argument is a '|'-separated list of channel names in order as they are given as additional stream inputs for filter. This also specify number of input streams. Number of input streams must be not less than number of channels in first stream plus one. @item gain Set gain applied to audio. Value is in dB. Default is 0. @item type Set processing type. Can be @var{time} or @var{freq}. @var{time} is processing audio in time domain which is slow. @var{freq} is processing audio in frequency domain which is fast. Default is @var{freq}. @item lfe Set custom gain for LFE channels. Value is in dB. Default is 0. @end table @subsection Examples @itemize @item Full example using wav files as coefficients with amovie filters for 7.1 downmix, each amovie filter use stereo file with IR coefficients as input. The files give coefficients for each position of virtual loudspeaker: @example ffmpeg -i input.wav -lavfi-complex "amovie=azi_270_ele_0_DFC.wav[sr],amovie=azi_90_ele_0_DFC.wav[sl],amovie=azi_225_ele_0_DFC.wav[br],amovie=azi_135_ele_0_DFC.wav[bl],amovie=azi_0_ele_0_DFC.wav,asplit[fc][lfe],amovie=azi_35_ele_0_DFC.wav[fl],amovie=azi_325_ele_0_DFC.wav[fr],[a:0][fl][fr][fc][lfe][bl][br][sl][sr]headphone=FL|FR|FC|LFE|BL|BR|SL|SR" output.wav @end example @end itemize @section highpass Apply a high-pass filter with 3dB point frequency. The filter can be either single-pole, or double-pole (the default). The filter roll off at 6dB per pole per octave (20dB per pole per decade). The filter accepts the following options: @table @option @item frequency, f Set frequency in Hz. Default is 3000. @item poles, p Set number of poles. Default is 2. @item width_type, t Set method to specify band-width of filter. @table @option @item h Hz @item q Q-Factor @item o octave @item s slope @item k kHz @end table @item width, w Specify the band-width of a filter in width_type units. Applies only to double-pole filter. The default is 0.707q and gives a Butterworth response. @item channels, c Specify which channels to filter, by default all available are filtered. @end table @subsection Commands This filter supports the following commands: @table @option @item frequency, f Change highpass frequency. Syntax for the command is : "@var{frequency}" @item width_type, t Change highpass width_type. Syntax for the command is : "@var{width_type}" @item width, w Change highpass width. Syntax for the command is : "@var{width}" @end table @section join Join multiple input streams into one multi-channel stream. It accepts the following parameters: @table @option @item inputs The number of input streams. It defaults to 2. @item channel_layout The desired output channel layout. It defaults to stereo. @item map Map channels from inputs to output. The argument is a '|'-separated list of mappings, each in the @code{@var{input_idx}.@var{in_channel}-@var{out_channel}} form. @var{input_idx} is the 0-based index of the input stream. @var{in_channel} can be either the name of the input channel (e.g. FL for front left) or its index in the specified input stream. @var{out_channel} is the name of the output channel. @end table The filter will attempt to guess the mappings when they are not specified explicitly. It does so by first trying to find an unused matching input channel and if that fails it picks the first unused input channel. Join 3 inputs (with properly set channel layouts): @example ffmpeg -i INPUT1 -i INPUT2 -i INPUT3 -filter_complex join=inputs=3 OUTPUT @end example Build a 5.1 output from 6 single-channel streams: @example ffmpeg -i fl -i fr -i fc -i sl -i sr -i lfe -filter_complex 'join=inputs=6:channel_layout=5.1:map=0.0-FL|1.0-FR|2.0-FC|3.0-SL|4.0-SR|5.0-LFE' out @end example @section ladspa Load a LADSPA (Linux Audio Developer's Simple Plugin API) plugin. To enable compilation of this filter you need to configure FFmpeg with @code{--enable-ladspa}. @table @option @item file, f Specifies the name of LADSPA plugin library to load. If the environment variable @env{LADSPA_PATH} is defined, the LADSPA plugin is searched in each one of the directories specified by the colon separated list in @env{LADSPA_PATH}, otherwise in the standard LADSPA paths, which are in this order: @file{HOME/.ladspa/lib/}, @file{/usr/local/lib/ladspa/}, @file{/usr/lib/ladspa/}. @item plugin, p Specifies the plugin within the library. Some libraries contain only one plugin, but others contain many of them. If this is not set filter will list all available plugins within the specified library. @item controls, c Set the '|' separated list of controls which are zero or more floating point values that determine the behavior of the loaded plugin (for example delay, threshold or gain). Controls need to be defined using the following syntax: c0=@var{value0}|c1=@var{value1}|c2=@var{value2}|..., where @var{valuei} is the value set on the @var{i}-th control. Alternatively they can be also defined using the following syntax: @var{value0}|@var{value1}|@var{value2}|..., where @var{valuei} is the value set on the @var{i}-th control. If @option{controls} is set to @code{help}, all available controls and their valid ranges are printed. @item sample_rate, s Specify the sample rate, default to 44100. Only used if plugin have zero inputs. @item nb_samples, n Set the number of samples per channel per each output frame, default is 1024. Only used if plugin have zero inputs. @item duration, d Set the minimum duration of the sourced audio. See @ref{time duration syntax,,the Time duration section in the ffmpeg-utils(1) manual,ffmpeg-utils} for the accepted syntax. Note that the resulting duration may be greater than the specified duration, as the generated audio is always cut at the end of a complete frame. If not specified, or the expressed duration is negative, the audio is supposed to be generated forever. Only used if plugin have zero inputs. @end table @subsection Examples @itemize @item List all available plugins within amp (LADSPA example plugin) library: @example ladspa=file=amp @end example @item List all available controls and their valid ranges for @code{vcf_notch} plugin from @code{VCF} library: @example ladspa=f=vcf:p=vcf_notch:c=help @end example @item Simulate low quality audio equipment using @code{Computer Music Toolkit} (CMT) plugin library: @example ladspa=file=cmt:plugin=lofi:controls=c0=22|c1=12|c2=12 @end example @item Add reverberation to the audio using TAP-plugins (Tom's Audio Processing plugins): @example ladspa=file=tap_reverb:tap_reverb @end example @item Generate white noise, with 0.2 amplitude: @example ladspa=file=cmt:noise_source_white:c=c0=.2 @end example @item Generate 20 bpm clicks using plugin @code{C* Click - Metronome} from the @code{C* Audio Plugin Suite} (CAPS) library: @example ladspa=file=caps:Click:c=c1=20' @end example @item Apply @code{C* Eq10X2 - Stereo 10-band equaliser} effect: @example ladspa=caps:Eq10X2:c=c0=-48|c9=-24|c3=12|c4=2 @end example @item Increase volume by 20dB using fast lookahead limiter from Steve Harris @code{SWH Plugins} collection: @example ladspa=fast_lookahead_limiter_1913:fastLookaheadLimiter:20|0|2 @end example @item Attenuate low frequencies using Multiband EQ from Steve Harris @code{SWH Plugins} collection: @example ladspa=mbeq_1197:mbeq:-24|-24|-24|0|0|0|0|0|0|0|0|0|0|0|0 @end example @item Reduce stereo image using @code{Narrower} from the @code{C* Audio Plugin Suite} (CAPS) library: @example ladspa=caps:Narrower @end example @item Another white noise, now using @code{C* Audio Plugin Suite} (CAPS) library: @example ladspa=caps:White:.2 @end example @item Some fractal noise, using @code{C* Audio Plugin Suite} (CAPS) library: @example ladspa=caps:Fractal:c=c1=1 @end example @item Dynamic volume normalization using @code{VLevel} plugin: @example ladspa=vlevel-ladspa:vlevel_mono @end example @end itemize @subsection Commands This filter supports the following commands: @table @option @item cN Modify the @var{N}-th control value. If the specified value is not valid, it is ignored and prior one is kept. @end table @section loudnorm EBU R128 loudness normalization. Includes both dynamic and linear normalization modes. Support for both single pass (livestreams, files) and double pass (files) modes. This algorithm can target IL, LRA, and maximum true peak. To accurately detect true peaks, the audio stream will be upsampled to 192 kHz unless the normalization mode is linear. Use the @code{-ar} option or @code{aresample} filter to explicitly set an output sample rate. The filter accepts the following options: @table @option @item I, i Set integrated loudness target. Range is -70.0 - -5.0. Default value is -24.0. @item LRA, lra Set loudness range target. Range is 1.0 - 20.0. Default value is 7.0. @item TP, tp Set maximum true peak. Range is -9.0 - +0.0. Default value is -2.0. @item measured_I, measured_i Measured IL of input file. Range is -99.0 - +0.0. @item measured_LRA, measured_lra Measured LRA of input file. Range is 0.0 - 99.0. @item measured_TP, measured_tp Measured true peak of input file. Range is -99.0 - +99.0. @item measured_thresh Measured threshold of input file. Range is -99.0 - +0.0. @item offset Set offset gain. Gain is applied before the true-peak limiter. Range is -99.0 - +99.0. Default is +0.0. @item linear Normalize linearly if possible. measured_I, measured_LRA, measured_TP, and measured_thresh must also to be specified in order to use this mode. Options are true or false. Default is true. @item dual_mono Treat mono input files as "dual-mono". If a mono file is intended for playback on a stereo system, its EBU R128 measurement will be perceptually incorrect. If set to @code{true}, this option will compensate for this effect. Multi-channel input files are not affected by this option. Options are true or false. Default is false. @item print_format Set print format for stats. Options are summary, json, or none. Default value is none. @end table @section lowpass Apply a low-pass filter with 3dB point frequency. The filter can be either single-pole or double-pole (the default). The filter roll off at 6dB per pole per octave (20dB per pole per decade). The filter accepts the following options: @table @option @item frequency, f Set frequency in Hz. Default is 500. @item poles, p Set number of poles. Default is 2. @item width_type, t Set method to specify band-width of filter. @table @option @item h Hz @item q Q-Factor @item o octave @item s slope @item k kHz @end table @item width, w Specify the band-width of a filter in width_type units. Applies only to double-pole filter. The default is 0.707q and gives a Butterworth response. @item channels, c Specify which channels to filter, by default all available are filtered. @end table @subsection Examples @itemize @item Lowpass only LFE channel, it LFE is not present it does nothing: @example lowpass=c=LFE @end example @end itemize @subsection Commands This filter supports the following commands: @table @option @item frequency, f Change lowpass frequency. Syntax for the command is : "@var{frequency}" @item width_type, t Change lowpass width_type. Syntax for the command is : "@var{width_type}" @item width, w Change lowpass width. Syntax for the command is : "@var{width}" @end table @section lv2 Load a LV2 (LADSPA Version 2) plugin. To enable compilation of this filter you need to configure FFmpeg with @code{--enable-lv2}. @table @option @item plugin, p Specifies the plugin URI. You may need to escape ':'. @item controls, c Set the '|' separated list of controls which are zero or more floating point values that determine the behavior of the loaded plugin (for example delay, threshold or gain). If @option{controls} is set to @code{help}, all available controls and their valid ranges are printed. @item sample_rate, s Specify the sample rate, default to 44100. Only used if plugin have zero inputs. @item nb_samples, n Set the number of samples per channel per each output frame, default is 1024. Only used if plugin have zero inputs. @item duration, d Set the minimum duration of the sourced audio. See @ref{time duration syntax,,the Time duration section in the ffmpeg-utils(1) manual,ffmpeg-utils} for the accepted syntax. Note that the resulting duration may be greater than the specified duration, as the generated audio is always cut at the end of a complete frame. If not specified, or the expressed duration is negative, the audio is supposed to be generated forever. Only used if plugin have zero inputs. @end table @subsection Examples @itemize @item Apply bass enhancer plugin from Calf: @example lv2=p=http\\\\://calf.sourceforge.net/plugins/BassEnhancer:c=amount=2 @end example @item Apply vinyl plugin from Calf: @example lv2=p=http\\\\://calf.sourceforge.net/plugins/Vinyl:c=drone=0.2|aging=0.5 @end example @item Apply bit crusher plugin from ArtyFX: @example lv2=p=http\\\\://www.openavproductions.com/artyfx#bitta:c=crush=0.3 @end example @end itemize @section mcompand Multiband Compress or expand the audio's dynamic range. The input audio is divided into bands using 4th order Linkwitz-Riley IIRs. This is akin to the crossover of a loudspeaker, and results in flat frequency response when absent compander action. It accepts the following parameters: @table @option @item args This option syntax is: attack,decay,[attack,decay..] soft-knee points crossover_frequency [delay [initial_volume [gain]]] | attack,decay ... For explanation of each item refer to compand filter documentation. @end table @anchor{pan} @section pan Mix channels with specific gain levels. The filter accepts the output channel layout followed by a set of channels definitions. This filter is also designed to efficiently remap the channels of an audio stream. The filter accepts parameters of the form: "@var{l}|@var{outdef}|@var{outdef}|..." @table @option @item l output channel layout or number of channels @item outdef output channel specification, of the form: "@var{out_name}=[@var{gain}*]@var{in_name}[(+-)[@var{gain}*]@var{in_name}...]" @item out_name output channel to define, either a channel name (FL, FR, etc.) or a channel number (c0, c1, etc.) @item gain multiplicative coefficient for the channel, 1 leaving the volume unchanged @item in_name input channel to use, see out_name for details; it is not possible to mix named and numbered input channels @end table If the `=' in a channel specification is replaced by `<', then the gains for that specification will be renormalized so that the total is 1, thus avoiding clipping noise. @subsection Mixing examples For example, if you want to down-mix from stereo to mono, but with a bigger factor for the left channel: @example pan=1c|c0=0.9*c0+0.1*c1 @end example A customized down-mix to stereo that works automatically for 3-, 4-, 5- and 7-channels surround: @example pan=stereo| FL < FL + 0.5*FC + 0.6*BL + 0.6*SL | FR < FR + 0.5*FC + 0.6*BR + 0.6*SR @end example Note that @command{ffmpeg} integrates a default down-mix (and up-mix) system that should be preferred (see "-ac" option) unless you have very specific needs. @subsection Remapping examples The channel remapping will be effective if, and only if: @itemize @item gain coefficients are zeroes or ones, @item only one input per channel output, @end itemize If all these conditions are satisfied, the filter will notify the user ("Pure channel mapping detected"), and use an optimized and lossless method to do the remapping. For example, if you have a 5.1 source and want a stereo audio stream by dropping the extra channels: @example pan="stereo| c0=FL | c1=FR" @end example Given the same source, you can also switch front left and front right channels and keep the input channel layout: @example pan="5.1| c0=c1 | c1=c0 | c2=c2 | c3=c3 | c4=c4 | c5=c5" @end example If the input is a stereo audio stream, you can mute the front left channel (and still keep the stereo channel layout) with: @example pan="stereo|c1=c1" @end example Still with a stereo audio stream input, you can copy the right channel in both front left and right: @example pan="stereo| c0=FR | c1=FR" @end example @section replaygain ReplayGain scanner filter. This filter takes an audio stream as an input and outputs it unchanged. At end of filtering it displays @code{track_gain} and @code{track_peak}. @section resample Convert the audio sample format, sample rate and channel layout. It is not meant to be used directly. @section rubberband Apply time-stretching and pitch-shifting with librubberband. The filter accepts the following options: @table @option @item tempo Set tempo scale factor. @item pitch Set pitch scale factor. @item transients Set transients detector. Possible values are: @table @var @item crisp @item mixed @item smooth @end table @item detector Set detector. Possible values are: @table @var @item compound @item percussive @item soft @end table @item phase Set phase. Possible values are: @table @var @item laminar @item independent @end table @item window Set processing window size. Possible values are: @table @var @item standard @item short @item long @end table @item smoothing Set smoothing. Possible values are: @table @var @item off @item on @end table @item formant Enable formant preservation when shift pitching. Possible values are: @table @var @item shifted @item preserved @end table @item pitchq Set pitch quality. Possible values are: @table @var @item quality @item speed @item consistency @end table @item channels Set channels. Possible values are: @table @var @item apart @item together @end table @end table @section sidechaincompress This filter acts like normal compressor but has the ability to compress detected signal using second input signal. It needs two input streams and returns one output stream. First input stream will be processed depending on second stream signal. The filtered signal then can be filtered with other filters in later stages of processing. See @ref{pan} and @ref{amerge} filter. The filter accepts the following options: @table @option @item level_in Set input gain. Default is 1. Range is between 0.015625 and 64. @item threshold If a signal of second stream raises above this level it will affect the gain reduction of first stream. By default is 0.125. Range is between 0.00097563 and 1. @item ratio Set a ratio about which the signal is reduced. 1:2 means that if the level raised 4dB above the threshold, it will be only 2dB above after the reduction. Default is 2. Range is between 1 and 20. @item attack Amount of milliseconds the signal has to rise above the threshold before gain reduction starts. Default is 20. Range is between 0.01 and 2000. @item release Amount of milliseconds the signal has to fall below the threshold before reduction is decreased again. Default is 250. Range is between 0.01 and 9000. @item makeup Set the amount by how much signal will be amplified after processing. Default is 1. Range is from 1 to 64. @item knee Curve the sharp knee around the threshold to enter gain reduction more softly. Default is 2.82843. Range is between 1 and 8. @item link Choose if the @code{average} level between all channels of side-chain stream or the louder(@code{maximum}) channel of side-chain stream affects the reduction. Default is @code{average}. @item detection Should the exact signal be taken in case of @code{peak} or an RMS one in case of @code{rms}. Default is @code{rms} which is mainly smoother. @item level_sc Set sidechain gain. Default is 1. Range is between 0.015625 and 64. @item mix How much to use compressed signal in output. Default is 1. Range is between 0 and 1. @end table @subsection Examples @itemize @item Full ffmpeg example taking 2 audio inputs, 1st input to be compressed depending on the signal of 2nd input and later compressed signal to be merged with 2nd input: @example ffmpeg -i main.flac -i sidechain.flac -filter_complex "[1:a]asplit=2[sc][mix];[0:a][sc]sidechaincompress[compr];[compr][mix]amerge" @end example @end itemize @section sidechaingate A sidechain gate acts like a normal (wideband) gate but has the ability to filter the detected signal before sending it to the gain reduction stage. Normally a gate uses the full range signal to detect a level above the threshold. For example: If you cut all lower frequencies from your sidechain signal the gate will decrease the volume of your track only if not enough highs appear. With this technique you are able to reduce the resonation of a natural drum or remove "rumbling" of muted strokes from a heavily distorted guitar. It needs two input streams and returns one output stream. First input stream will be processed depending on second stream signal. The filter accepts the following options: @table @option @item level_in Set input level before filtering. Default is 1. Allowed range is from 0.015625 to 64. @item range Set the level of gain reduction when the signal is below the threshold. Default is 0.06125. Allowed range is from 0 to 1. @item threshold If a signal rises above this level the gain reduction is released. Default is 0.125. Allowed range is from 0 to 1. @item ratio Set a ratio about which the signal is reduced. Default is 2. Allowed range is from 1 to 9000. @item attack Amount of milliseconds the signal has to rise above the threshold before gain reduction stops. Default is 20 milliseconds. Allowed range is from 0.01 to 9000. @item release Amount of milliseconds the signal has to fall below the threshold before the reduction is increased again. Default is 250 milliseconds. Allowed range is from 0.01 to 9000. @item makeup Set amount of amplification of signal after processing. Default is 1. Allowed range is from 1 to 64. @item knee Curve the sharp knee around the threshold to enter gain reduction more softly. Default is 2.828427125. Allowed range is from 1 to 8. @item detection Choose if exact signal should be taken for detection or an RMS like one. Default is rms. Can be peak or rms. @item link Choose if the average level between all channels or the louder channel affects the reduction. Default is average. Can be average or maximum. @item level_sc Set sidechain gain. Default is 1. Range is from 0.015625 to 64. @end table @section silencedetect Detect silence in an audio stream. This filter logs a message when it detects that the input audio volume is less or equal to a noise tolerance value for a duration greater or equal to the minimum detected noise duration. The printed times and duration are expressed in seconds. The filter accepts the following options: @table @option @item duration, d Set silence duration until notification (default is 2 seconds). @item noise, n Set noise tolerance. Can be specified in dB (in case "dB" is appended to the specified value) or amplitude ratio. Default is -60dB, or 0.001. @end table @subsection Examples @itemize @item Detect 5 seconds of silence with -50dB noise tolerance: @example silencedetect=n=-50dB:d=5 @end example @item Complete example with @command{ffmpeg} to detect silence with 0.0001 noise tolerance in @file{silence.mp3}: @example ffmpeg -i silence.mp3 -af silencedetect=noise=0.0001 -f null - @end example @end itemize @section silenceremove Remove silence from the beginning, middle or end of the audio. The filter accepts the following options: @table @option @item start_periods This value is used to indicate if audio should be trimmed at beginning of the audio. A value of zero indicates no silence should be trimmed from the beginning. When specifying a non-zero value, it trims audio up until it finds non-silence. Normally, when trimming silence from beginning of audio the @var{start_periods} will be @code{1} but it can be increased to higher values to trim all audio up to specific count of non-silence periods. Default value is @code{0}. @item start_duration Specify the amount of time that non-silence must be detected before it stops trimming audio. By increasing the duration, bursts of noises can be treated as silence and trimmed off. Default value is @code{0}. @item start_threshold This indicates what sample value should be treated as silence. For digital audio, a value of @code{0} may be fine but for audio recorded from analog, you may wish to increase the value to account for background noise. Can be specified in dB (in case "dB" is appended to the specified value) or amplitude ratio. Default value is @code{0}. @item stop_periods Set the count for trimming silence from the end of audio. To remove silence from the middle of a file, specify a @var{stop_periods} that is negative. This value is then treated as a positive value and is used to indicate the effect should restart processing as specified by @var{start_periods}, making it suitable for removing periods of silence in the middle of the audio. Default value is @code{0}. @item stop_duration Specify a duration of silence that must exist before audio is not copied any more. By specifying a higher duration, silence that is wanted can be left in the audio. Default value is @code{0}. @item stop_threshold This is the same as @option{start_threshold} but for trimming silence from the end of audio. Can be specified in dB (in case "dB" is appended to the specified value) or amplitude ratio. Default value is @code{0}. @item leave_silence This indicates that @var{stop_duration} length of audio should be left intact at the beginning of each period of silence. For example, if you want to remove long pauses between words but do not want to remove the pauses completely. Default value is @code{0}. @item detection Set how is silence detected. Can be @code{rms} or @code{peak}. Second is faster and works better with digital silence which is exactly 0. Default value is @code{rms}. @item window Set ratio used to calculate size of window for detecting silence. Default value is @code{0.02}. Allowed range is from @code{0} to @code{10}. @end table @subsection Examples @itemize @item The following example shows how this filter can be used to start a recording that does not contain the delay at the start which usually occurs between pressing the record button and the start of the performance: @example silenceremove=1:5:0.02 @end example @item Trim all silence encountered from beginning to end where there is more than 1 second of silence in audio: @example silenceremove=0:0:0:-1:1:-90dB @end example @end itemize @section sofalizer SOFAlizer uses head-related transfer functions (HRTFs) to create virtual loudspeakers around the user for binaural listening via headphones (audio formats up to 9 channels supported). The HRTFs are stored in SOFA files (see @url{http://www.sofacoustics.org/} for a database). SOFAlizer is developed at the Acoustics Research Institute (ARI) of the Austrian Academy of Sciences. To enable compilation of this filter you need to configure FFmpeg with @code{--enable-libmysofa}. The filter accepts the following options: @table @option @item sofa Set the SOFA file used for rendering. @item gain Set gain applied to audio. Value is in dB. Default is 0. @item rotation Set rotation of virtual loudspeakers in deg. Default is 0. @item elevation Set elevation of virtual speakers in deg. Default is 0. @item radius Set distance in meters between loudspeakers and the listener with near-field HRTFs. Default is 1. @item type Set processing type. Can be @var{time} or @var{freq}. @var{time} is processing audio in time domain which is slow. @var{freq} is processing audio in frequency domain which is fast. Default is @var{freq}. @item speakers Set custom positions of virtual loudspeakers. Syntax for this option is: [| |...]. Each virtual loudspeaker is described with short channel name following with azimuth and elevation in degrees. Each virtual loudspeaker description is separated by '|'. For example to override front left and front right channel positions use: 'speakers=FL 45 15|FR 345 15'. Descriptions with unrecognised channel names are ignored. @item lfegain Set custom gain for LFE channels. Value is in dB. Default is 0. @end table @subsection Examples @itemize @item Using ClubFritz6 sofa file: @example sofalizer=sofa=/path/to/ClubFritz6.sofa:type=freq:radius=1 @end example @item Using ClubFritz12 sofa file and bigger radius with small rotation: @example sofalizer=sofa=/path/to/ClubFritz12.sofa:type=freq:radius=2:rotation=5 @end example @item Similar as above but with custom speaker positions for front left, front right, back left and back right and also with custom gain: @example "sofalizer=sofa=/path/to/ClubFritz6.sofa:type=freq:radius=2:speakers=FL 45|FR 315|BL 135|BR 225:gain=28" @end example @end itemize @section stereotools This filter has some handy utilities to manage stereo signals, for converting M/S stereo recordings to L/R signal while having control over the parameters or spreading the stereo image of master track. The filter accepts the following options: @table @option @item level_in Set input level before filtering for both channels. Defaults is 1. Allowed range is from 0.015625 to 64. @item level_out Set output level after filtering for both channels. Defaults is 1. Allowed range is from 0.015625 to 64. @item balance_in Set input balance between both channels. Default is 0. Allowed range is from -1 to 1. @item balance_out Set output balance between both channels. Default is 0. Allowed range is from -1 to 1. @item softclip Enable softclipping. Results in analog distortion instead of harsh digital 0dB clipping. Disabled by default. @item mutel Mute the left channel. Disabled by default. @item muter Mute the right channel. Disabled by default. @item phasel Change the phase of the left channel. Disabled by default. @item phaser Change the phase of the right channel. Disabled by default. @item mode Set stereo mode. Available values are: @table @samp @item lr>lr Left/Right to Left/Right, this is default. @item lr>ms Left/Right to Mid/Side. @item ms>lr Mid/Side to Left/Right. @item lr>ll Left/Right to Left/Left. @item lr>rr Left/Right to Right/Right. @item lr>l+r Left/Right to Left + Right. @item lr>rl Left/Right to Right/Left. @item ms>ll Mid/Side to Left/Left. @item ms>rr Mid/Side to Right/Right. @end table @item slev Set level of side signal. Default is 1. Allowed range is from 0.015625 to 64. @item sbal Set balance of side signal. Default is 0. Allowed range is from -1 to 1. @item mlev Set level of the middle signal. Default is 1. Allowed range is from 0.015625 to 64. @item mpan Set middle signal pan. Default is 0. Allowed range is from -1 to 1. @item base Set stereo base between mono and inversed channels. Default is 0. Allowed range is from -1 to 1. @item delay Set delay in milliseconds how much to delay left from right channel and vice versa. Default is 0. Allowed range is from -20 to 20. @item sclevel Set S/C level. Default is 1. Allowed range is from 1 to 100. @item phase Set the stereo phase in degrees. Default is 0. Allowed range is from 0 to 360. @item bmode_in, bmode_out Set balance mode for balance_in/balance_out option. Can be one of the following: @table @samp @item balance Classic balance mode. Attenuate one channel at time. Gain is raised up to 1. @item amplitude Similar as classic mode above but gain is raised up to 2. @item power Equal power distribution, from -6dB to +6dB range. @end table @end table @subsection Examples @itemize @item Apply karaoke like effect: @example stereotools=mlev=0.015625 @end example @item Convert M/S signal to L/R: @example "stereotools=mode=ms>lr" @end example @end itemize @section stereowiden This filter enhance the stereo effect by suppressing signal common to both channels and by delaying the signal of left into right and vice versa, thereby widening the stereo effect. The filter accepts the following options: @table @option @item delay Time in milliseconds of the delay of left signal into right and vice versa. Default is 20 milliseconds. @item feedback Amount of gain in delayed signal into right and vice versa. Gives a delay effect of left signal in right output and vice versa which gives widening effect. Default is 0.3. @item crossfeed Cross feed of left into right with inverted phase. This helps in suppressing the mono. If the value is 1 it will cancel all the signal common to both channels. Default is 0.3. @item drymix Set level of input signal of original channel. Default is 0.8. @end table @section superequalizer Apply 18 band equalizer. The filter accepts the following options: @table @option @item 1b Set 65Hz band gain. @item 2b Set 92Hz band gain. @item 3b Set 131Hz band gain. @item 4b Set 185Hz band gain. @item 5b Set 262Hz band gain. @item 6b Set 370Hz band gain. @item 7b Set 523Hz band gain. @item 8b Set 740Hz band gain. @item 9b Set 1047Hz band gain. @item 10b Set 1480Hz band gain. @item 11b Set 2093Hz band gain. @item 12b Set 2960Hz band gain. @item 13b Set 4186Hz band gain. @item 14b Set 5920Hz band gain. @item 15b Set 8372Hz band gain. @item 16b Set 11840Hz band gain. @item 17b Set 16744Hz band gain. @item 18b Set 20000Hz band gain. @end table @section surround Apply audio surround upmix filter. This filter allows to produce multichannel output from audio stream. The filter accepts the following options: @table @option @item chl_out Set output channel layout. By default, this is @var{5.1}. See @ref{channel layout syntax,,the Channel Layout section in the ffmpeg-utils(1) manual,ffmpeg-utils} for the required syntax. @item chl_in Set input channel layout. By default, this is @var{stereo}. See @ref{channel layout syntax,,the Channel Layout section in the ffmpeg-utils(1) manual,ffmpeg-utils} for the required syntax. @item level_in Set input volume level. By default, this is @var{1}. @item level_out Set output volume level. By default, this is @var{1}. @item lfe Enable LFE channel output if output channel layout has it. By default, this is enabled. @item lfe_low Set LFE low cut off frequency. By default, this is @var{128} Hz. @item lfe_high Set LFE high cut off frequency. By default, this is @var{256} Hz. @item fc_in Set front center input volume. By default, this is @var{1}. @item fc_out Set front center output volume. By default, this is @var{1}. @item lfe_in Set LFE input volume. By default, this is @var{1}. @item lfe_out Set LFE output volume. By default, this is @var{1}. @end table @section treble Boost or cut treble (upper) frequencies of the audio using a two-pole shelving filter with a response similar to that of a standard hi-fi's tone-controls. This is also known as shelving equalisation (EQ). The filter accepts the following options: @table @option @item gain, g Give the gain at whichever is the lower of ~22 kHz and the Nyquist frequency. Its useful range is about -20 (for a large cut) to +20 (for a large boost). Beware of clipping when using a positive gain. @item frequency, f Set the filter's central frequency and so can be used to extend or reduce the frequency range to be boosted or cut. The default value is @code{3000} Hz. @item width_type, t Set method to specify band-width of filter. @table @option @item h Hz @item q Q-Factor @item o octave @item s slope @item k kHz @end table @item width, w Determine how steep is the filter's shelf transition. @item channels, c Specify which channels to filter, by default all available are filtered. @end table @subsection Commands This filter supports the following commands: @table @option @item frequency, f Change treble frequency. Syntax for the command is : "@var{frequency}" @item width_type, t Change treble width_type. Syntax for the command is : "@var{width_type}" @item width, w Change treble width. Syntax for the command is : "@var{width}" @item gain, g Change treble gain. Syntax for the command is : "@var{gain}" @end table @section tremolo Sinusoidal amplitude modulation. The filter accepts the following options: @table @option @item f Modulation frequency in Hertz. Modulation frequencies in the subharmonic range (20 Hz or lower) will result in a tremolo effect. This filter may also be used as a ring modulator by specifying a modulation frequency higher than 20 Hz. Range is 0.1 - 20000.0. Default value is 5.0 Hz. @item d Depth of modulation as a percentage. Range is 0.0 - 1.0. Default value is 0.5. @end table @section vibrato Sinusoidal phase modulation. The filter accepts the following options: @table @option @item f Modulation frequency in Hertz. Range is 0.1 - 20000.0. Default value is 5.0 Hz. @item d Depth of modulation as a percentage. Range is 0.0 - 1.0. Default value is 0.5. @end table @section volume Adjust the input audio volume. It accepts the following parameters: @table @option @item volume Set audio volume expression. Output values are clipped to the maximum value. The output audio volume is given by the relation: @example @var{output_volume} = @var{volume} * @var{input_volume} @end example The default value for @var{volume} is "1.0". @item precision This parameter represents the mathematical precision. It determines which input sample formats will be allowed, which affects the precision of the volume scaling. @table @option @item fixed 8-bit fixed-point; this limits input sample format to U8, S16, and S32. @item float 32-bit floating-point; this limits input sample format to FLT. (default) @item double 64-bit floating-point; this limits input sample format to DBL. @end table @item replaygain Choose the behaviour on encountering ReplayGain side data in input frames. @table @option @item drop Remove ReplayGain side data, ignoring its contents (the default). @item ignore Ignore ReplayGain side data, but leave it in the frame. @item track Prefer the track gain, if present. @item album Prefer the album gain, if present. @end table @item replaygain_preamp Pre-amplification gain in dB to apply to the selected replaygain gain. Default value for @var{replaygain_preamp} is 0.0. @item eval Set when the volume expression is evaluated. It accepts the following values: @table @samp @item once only evaluate expression once during the filter initialization, or when the @samp{volume} command is sent @item frame evaluate expression for each incoming frame @end table Default value is @samp{once}. @end table The volume expression can contain the following parameters. @table @option @item n frame number (starting at zero) @item nb_channels number of channels @item nb_consumed_samples number of samples consumed by the filter @item nb_samples number of samples in the current frame @item pos original frame position in the file @item pts frame PTS @item sample_rate sample rate @item startpts PTS at start of stream @item startt time at start of stream @item t frame time @item tb timestamp timebase @item volume last set volume value @end table Note that when @option{eval} is set to @samp{once} only the @var{sample_rate} and @var{tb} variables are available, all other variables will evaluate to NAN. @subsection Commands This filter supports the following commands: @table @option @item volume Modify the volume expression. The command accepts the same syntax of the corresponding option. If the specified expression is not valid, it is kept at its current value. @item replaygain_noclip Prevent clipping by limiting the gain applied. Default value for @var{replaygain_noclip} is 1. @end table @subsection Examples @itemize @item Halve the input audio volume: @example volume=volume=0.5 volume=volume=1/2 volume=volume=-6.0206dB @end example In all the above example the named key for @option{volume} can be omitted, for example like in: @example volume=0.5 @end example @item Increase input audio power by 6 decibels using fixed-point precision: @example volume=volume=6dB:precision=fixed @end example @item Fade volume after time 10 with an annihilation period of 5 seconds: @example volume='if(lt(t,10),1,max(1-(t-10)/5,0))':eval=frame @end example @end itemize @section volumedetect Detect the volume of the input video. The filter has no parameters. The input is not modified. Statistics about the volume will be printed in the log when the input stream end is reached. In particular it will show the mean volume (root mean square), maximum volume (on a per-sample basis), and the beginning of a histogram of the registered volume values (from the maximum value to a cumulated 1/1000 of the samples). All volumes are in decibels relative to the maximum PCM value. @subsection Examples Here is an excerpt of the output: @example [Parsed_volumedetect_0 @ 0xa23120] mean_volume: -27 dB [Parsed_volumedetect_0 @ 0xa23120] max_volume: -4 dB [Parsed_volumedetect_0 @ 0xa23120] histogram_4db: 6 [Parsed_volumedetect_0 @ 0xa23120] histogram_5db: 62 [Parsed_volumedetect_0 @ 0xa23120] histogram_6db: 286 [Parsed_volumedetect_0 @ 0xa23120] histogram_7db: 1042 [Parsed_volumedetect_0 @ 0xa23120] histogram_8db: 2551 [Parsed_volumedetect_0 @ 0xa23120] histogram_9db: 4609 [Parsed_volumedetect_0 @ 0xa23120] histogram_10db: 8409 @end example It means that: @itemize @item The mean square energy is approximately -27 dB, or 10^-2.7. @item The largest sample is at -4 dB, or more precisely between -4 dB and -5 dB. @item There are 6 samples at -4 dB, 62 at -5 dB, 286 at -6 dB, etc. @end itemize In other words, raising the volume by +4 dB does not cause any clipping, raising it by +5 dB causes clipping for 6 samples, etc. @c man end AUDIO FILTERS @chapter Audio Sources @c man begin AUDIO SOURCES Below is a description of the currently available audio sources. @section abuffer Buffer audio frames, and make them available to the filter chain. This source is mainly intended for a programmatic use, in particular through the interface defined in @file{libavfilter/asrc_abuffer.h}. It accepts the following parameters: @table @option @item time_base The timebase which will be used for timestamps of submitted frames. It must be either a floating-point number or in @var{numerator}/@var{denominator} form. @item sample_rate The sample rate of the incoming audio buffers. @item sample_fmt The sample format of the incoming audio buffers. Either a sample format name or its corresponding integer representation from the enum AVSampleFormat in @file{libavutil/samplefmt.h} @item channel_layout The channel layout of the incoming audio buffers. Either a channel layout name from channel_layout_map in @file{libavutil/channel_layout.c} or its corresponding integer representation from the AV_CH_LAYOUT_* macros in @file{libavutil/channel_layout.h} @item channels The number of channels of the incoming audio buffers. If both @var{channels} and @var{channel_layout} are specified, then they must be consistent. @end table @subsection Examples @example abuffer=sample_rate=44100:sample_fmt=s16p:channel_layout=stereo @end example will instruct the source to accept planar 16bit signed stereo at 44100Hz. Since the sample format with name "s16p" corresponds to the number 6 and the "stereo" channel layout corresponds to the value 0x3, this is equivalent to: @example abuffer=sample_rate=44100:sample_fmt=6:channel_layout=0x3 @end example @section aevalsrc Generate an audio signal specified by an expression. This source accepts in input one or more expressions (one for each channel), which are evaluated and used to generate a corresponding audio signal. This source accepts the following options: @table @option @item exprs Set the '|'-separated expressions list for each separate channel. In case the @option{channel_layout} option is not specified, the selected channel layout depends on the number of provided expressions. Otherwise the last specified expression is applied to the remaining output channels. @item channel_layout, c Set the channel layout. The number of channels in the specified layout must be equal to the number of specified expressions. @item duration, d Set the minimum duration of the sourced audio. See @ref{time duration syntax,,the Time duration section in the ffmpeg-utils(1) manual,ffmpeg-utils} for the accepted syntax. Note that the resulting duration may be greater than the specified duration, as the generated audio is always cut at the end of a complete frame. If not specified, or the expressed duration is negative, the audio is supposed to be generated forever. @item nb_samples, n Set the number of samples per channel per each output frame, default to 1024. @item sample_rate, s Specify the sample rate, default to 44100. @end table Each expression in @var{exprs} can contain the following constants: @table @option @item n number of the evaluated sample, starting from 0 @item t time of the evaluated sample expressed in seconds, starting from 0 @item s sample rate @end table @subsection Examples @itemize @item Generate silence: @example aevalsrc=0 @end example @item Generate a sin signal with frequency of 440 Hz, set sample rate to 8000 Hz: @example aevalsrc="sin(440*2*PI*t):s=8000" @end example @item Generate a two channels signal, specify the channel layout (Front Center + Back Center) explicitly: @example aevalsrc="sin(420*2*PI*t)|cos(430*2*PI*t):c=FC|BC" @end example @item Generate white noise: @example aevalsrc="-2+random(0)" @end example @item Generate an amplitude modulated signal: @example aevalsrc="sin(10*2*PI*t)*sin(880*2*PI*t)" @end example @item Generate 2.5 Hz binaural beats on a 360 Hz carrier: @example aevalsrc="0.1*sin(2*PI*(360-2.5/2)*t) | 0.1*sin(2*PI*(360+2.5/2)*t)" @end example @end itemize @section anullsrc The null audio source, return unprocessed audio frames. It is mainly useful as a template and to be employed in analysis / debugging tools, or as the source for filters which ignore the input data (for example the sox synth filter). This source accepts the following options: @table @option @item channel_layout, cl Specifies the channel layout, and can be either an integer or a string representing a channel layout. The default value of @var{channel_layout} is "stereo". Check the channel_layout_map definition in @file{libavutil/channel_layout.c} for the mapping between strings and channel layout values. @item sample_rate, r Specifies the sample rate, and defaults to 44100. @item nb_samples, n Set the number of samples per requested frames. @end table @subsection Examples @itemize @item Set the sample rate to 48000 Hz and the channel layout to AV_CH_LAYOUT_MONO. @example anullsrc=r=48000:cl=4 @end example @item Do the same operation with a more obvious syntax: @example anullsrc=r=48000:cl=mono @end example @end itemize All the parameters need to be explicitly defined. @section flite Synthesize a voice utterance using the libflite library. To enable compilation of this filter you need to configure FFmpeg with @code{--enable-libflite}. Note that versions of the flite library prior to 2.0 are not thread-safe. The filter accepts the following options: @table @option @item list_voices If set to 1, list the names of the available voices and exit immediately. Default value is 0. @item nb_samples, n Set the maximum number of samples per frame. Default value is 512. @item textfile Set the filename containing the text to speak. @item text Set the text to speak. @item voice, v Set the voice to use for the speech synthesis. Default value is @code{kal}. See also the @var{list_voices} option. @end table @subsection Examples @itemize @item Read from file @file{speech.txt}, and synthesize the text using the standard flite voice: @example flite=textfile=speech.txt @end example @item Read the specified text selecting the @code{slt} voice: @example flite=text='So fare thee well, poor devil of a Sub-Sub, whose commentator I am':voice=slt @end example @item Input text to ffmpeg: @example ffmpeg -f lavfi -i flite=text='So fare thee well, poor devil of a Sub-Sub, whose commentator I am':voice=slt @end example @item Make @file{ffplay} speak the specified text, using @code{flite} and the @code{lavfi} device: @example ffplay -f lavfi flite=text='No more be grieved for which that thou hast done.' @end example @end itemize For more information about libflite, check: @url{http://www.festvox.org/flite/} @section anoisesrc Generate a noise audio signal. The filter accepts the following options: @table @option @item sample_rate, r Specify the sample rate. Default value is 48000 Hz. @item amplitude, a Specify the amplitude (0.0 - 1.0) of the generated audio stream. Default value is 1.0. @item duration, d Specify the duration of the generated audio stream. Not specifying this option results in noise with an infinite length. @item color, colour, c Specify the color of noise. Available noise colors are white, pink, brown, blue and violet. Default color is white. @item seed, s Specify a value used to seed the PRNG. @item nb_samples, n Set the number of samples per each output frame, default is 1024. @end table @subsection Examples @itemize @item Generate 60 seconds of pink noise, with a 44.1 kHz sampling rate and an amplitude of 0.5: @example anoisesrc=d=60:c=pink:r=44100:a=0.5 @end example @end itemize @section hilbert Generate odd-tap Hilbert transform FIR coefficients. The resulting stream can be used with @ref{afir} filter for phase-shifting the signal by 90 degrees. This is used in many matrix coding schemes and for analytic signal generation. The process is often written as a multiplication by i (or j), the imaginary unit. The filter accepts the following options: @table @option @item sample_rate, s Set sample rate, default is 44100. @item taps, t Set length of FIR filter, default is 22051. @item nb_samples, n Set number of samples per each frame. @item win_func, w Set window function to be used when generating FIR coefficients. @end table @section sine Generate an audio signal made of a sine wave with amplitude 1/8. The audio signal is bit-exact. The filter accepts the following options: @table @option @item frequency, f Set the carrier frequency. Default is 440 Hz. @item beep_factor, b Enable a periodic beep every second with frequency @var{beep_factor} times the carrier frequency. Default is 0, meaning the beep is disabled. @item sample_rate, r Specify the sample rate, default is 44100. @item duration, d Specify the duration of the generated audio stream. @item samples_per_frame Set the number of samples per output frame. The expression can contain the following constants: @table @option @item n The (sequential) number of the output audio frame, starting from 0. @item pts The PTS (Presentation TimeStamp) of the output audio frame, expressed in @var{TB} units. @item t The PTS of the output audio frame, expressed in seconds. @item TB The timebase of the output audio frames. @end table Default is @code{1024}. @end table @subsection Examples @itemize @item Generate a simple 440 Hz sine wave: @example sine @end example @item Generate a 220 Hz sine wave with a 880 Hz beep each second, for 5 seconds: @example sine=220:4:d=5 sine=f=220:b=4:d=5 sine=frequency=220:beep_factor=4:duration=5 @end example @item Generate a 1 kHz sine wave following @code{1602,1601,1602,1601,1602} NTSC pattern: @example sine=1000:samples_per_frame='st(0,mod(n,5)); 1602-not(not(eq(ld(0),1)+eq(ld(0),3)))' @end example @end itemize @c man end AUDIO SOURCES @chapter Audio Sinks @c man begin AUDIO SINKS Below is a description of the currently available audio sinks. @section abuffersink Buffer audio frames, and make them available to the end of filter chain. This sink is mainly intended for programmatic use, in particular through the interface defined in @file{libavfilter/buffersink.h} or the options system. It accepts a pointer to an AVABufferSinkContext structure, which defines the incoming buffers' formats, to be passed as the opaque parameter to @code{avfilter_init_filter} for initialization. @section anullsink Null audio sink; do absolutely nothing with the input audio. It is mainly useful as a template and for use in analysis / debugging tools. @c man end AUDIO SINKS @chapter Video Filters @c man begin VIDEO FILTERS When you configure your FFmpeg build, you can disable any of the existing filters using @code{--disable-filters}. The configure output will show the video filters included in your build. Below is a description of the currently available video filters. @section alphaextract Extract the alpha component from the input as a grayscale video. This is especially useful with the @var{alphamerge} filter. @section alphamerge Add or replace the alpha component of the primary input with the grayscale value of a second input. This is intended for use with @var{alphaextract} to allow the transmission or storage of frame sequences that have alpha in a format that doesn't support an alpha channel. For example, to reconstruct full frames from a normal YUV-encoded video and a separate video created with @var{alphaextract}, you might use: @example movie=in_alpha.mkv [alpha]; [in][alpha] alphamerge [out] @end example Since this filter is designed for reconstruction, it operates on frame sequences without considering timestamps, and terminates when either input reaches end of stream. This will cause problems if your encoding pipeline drops frames. If you're trying to apply an image as an overlay to a video stream, consider the @var{overlay} filter instead. @section ass Same as the @ref{subtitles} filter, except that it doesn't require libavcodec and libavformat to work. On the other hand, it is limited to ASS (Advanced Substation Alpha) subtitles files. This filter accepts the following option in addition to the common options from the @ref{subtitles} filter: @table @option @item shaping Set the shaping engine Available values are: @table @samp @item auto The default libass shaping engine, which is the best available. @item simple Fast, font-agnostic shaper that can do only substitutions @item complex Slower shaper using OpenType for substitutions and positioning @end table The default is @code{auto}. @end table @section atadenoise Apply an Adaptive Temporal Averaging Denoiser to the video input. The filter accepts the following options: @table @option @item 0a Set threshold A for 1st plane. Default is 0.02. Valid range is 0 to 0.3. @item 0b Set threshold B for 1st plane. Default is 0.04. Valid range is 0 to 5. @item 1a Set threshold A for 2nd plane. Default is 0.02. Valid range is 0 to 0.3. @item 1b Set threshold B for 2nd plane. Default is 0.04. Valid range is 0 to 5. @item 2a Set threshold A for 3rd plane. Default is 0.02. Valid range is 0 to 0.3. @item 2b Set threshold B for 3rd plane. Default is 0.04. Valid range is 0 to 5. Threshold A is designed to react on abrupt changes in the input signal and threshold B is designed to react on continuous changes in the input signal. @item s Set number of frames filter will use for averaging. Default is 33. Must be odd number in range [5, 129]. @item p Set what planes of frame filter will use for averaging. Default is all. @end table @section avgblur Apply average blur filter. The filter accepts the following options: @table @option @item sizeX Set horizontal kernel size. @item planes Set which planes to filter. By default all planes are filtered. @item sizeY Set vertical kernel size, if zero it will be same as @code{sizeX}. Default is @code{0}. @end table @section bbox Compute the bounding box for the non-black pixels in the input frame luminance plane. This filter computes the bounding box containing all the pixels with a luminance value greater than the minimum allowed value. The parameters describing the bounding box are printed on the filter log. The filter accepts the following option: @table @option @item min_val Set the minimal luminance value. Default is @code{16}. @end table @section bitplanenoise Show and measure bit plane noise. The filter accepts the following options: @table @option @item bitplane Set which plane to analyze. Default is @code{1}. @item filter Filter out noisy pixels from @code{bitplane} set above. Default is disabled. @end table @section blackdetect Detect video intervals that are (almost) completely black. Can be useful to detect chapter transitions, commercials, or invalid recordings. Output lines contains the time for the start, end and duration of the detected black interval expressed in seconds. In order to display the output lines, you need to set the loglevel at least to the AV_LOG_INFO value. The filter accepts the following options: @table @option @item black_min_duration, d Set the minimum detected black duration expressed in seconds. It must be a non-negative floating point number. Default value is 2.0. @item picture_black_ratio_th, pic_th Set the threshold for considering a picture "black". Express the minimum value for the ratio: @example @var{nb_black_pixels} / @var{nb_pixels} @end example for which a picture is considered black. Default value is 0.98. @item pixel_black_th, pix_th Set the threshold for considering a pixel "black". The threshold expresses the maximum pixel luminance value for which a pixel is considered "black". The provided value is scaled according to the following equation: @example @var{absolute_threshold} = @var{luminance_minimum_value} + @var{pixel_black_th} * @var{luminance_range_size} @end example @var{luminance_range_size} and @var{luminance_minimum_value} depend on the input video format, the range is [0-255] for YUV full-range formats and [16-235] for YUV non full-range formats. Default value is 0.10. @end table The following example sets the maximum pixel threshold to the minimum value, and detects only black intervals of 2 or more seconds: @example blackdetect=d=2:pix_th=0.00 @end example @section blackframe Detect frames that are (almost) completely black. Can be useful to detect chapter transitions or commercials. Output lines consist of the frame number of the detected frame, the percentage of blackness, the position in the file if known or -1 and the timestamp in seconds. In order to display the output lines, you need to set the loglevel at least to the AV_LOG_INFO value. This filter exports frame metadata @code{lavfi.blackframe.pblack}. The value represents the percentage of pixels in the picture that are below the threshold value. It accepts the following parameters: @table @option @item amount The percentage of the pixels that have to be below the threshold; it defaults to @code{98}. @item threshold, thresh The threshold below which a pixel value is considered black; it defaults to @code{32}. @end table @section blend, tblend Blend two video frames into each other. The @code{blend} filter takes two input streams and outputs one stream, the first input is the "top" layer and second input is "bottom" layer. By default, the output terminates when the longest input terminates. The @code{tblend} (time blend) filter takes two consecutive frames from one single stream, and outputs the result obtained by blending the new frame on top of the old frame. A description of the accepted options follows. @table @option @item c0_mode @item c1_mode @item c2_mode @item c3_mode @item all_mode Set blend mode for specific pixel component or all pixel components in case of @var{all_mode}. Default value is @code{normal}. Available values for component modes are: @table @samp @item addition @item grainmerge @item and @item average @item burn @item darken @item difference @item grainextract @item divide @item dodge @item freeze @item exclusion @item extremity @item glow @item hardlight @item hardmix @item heat @item lighten @item linearlight @item multiply @item multiply128 @item negation @item normal @item or @item overlay @item phoenix @item pinlight @item reflect @item screen @item softlight @item subtract @item vividlight @item xor @end table @item c0_opacity @item c1_opacity @item c2_opacity @item c3_opacity @item all_opacity Set blend opacity for specific pixel component or all pixel components in case of @var{all_opacity}. Only used in combination with pixel component blend modes. @item c0_expr @item c1_expr @item c2_expr @item c3_expr @item all_expr Set blend expression for specific pixel component or all pixel components in case of @var{all_expr}. Note that related mode options will be ignored if those are set. The expressions can use the following variables: @table @option @item N The sequential number of the filtered frame, starting from @code{0}. @item X @item Y the coordinates of the current sample @item W @item H the width and height of currently filtered plane @item SW @item SH Width and height scale depending on the currently filtered plane. It is the ratio between the corresponding luma plane number of pixels and the current plane ones. E.g. for YUV4:2:0 the values are @code{1,1} for the luma plane, and @code{0.5,0.5} for chroma planes. @item T Time of the current frame, expressed in seconds. @item TOP, A Value of pixel component at current location for first video frame (top layer). @item BOTTOM, B Value of pixel component at current location for second video frame (bottom layer). @end table @end table The @code{blend} filter also supports the @ref{framesync} options. @subsection Examples @itemize @item Apply transition from bottom layer to top layer in first 10 seconds: @example blend=all_expr='A*(if(gte(T,10),1,T/10))+B*(1-(if(gte(T,10),1,T/10)))' @end example @item Apply linear horizontal transition from top layer to bottom layer: @example blend=all_expr='A*(X/W)+B*(1-X/W)' @end example @item Apply 1x1 checkerboard effect: @example blend=all_expr='if(eq(mod(X,2),mod(Y,2)),A,B)' @end example @item Apply uncover left effect: @example blend=all_expr='if(gte(N*SW+X,W),A,B)' @end example @item Apply uncover down effect: @example blend=all_expr='if(gte(Y-N*SH,0),A,B)' @end example @item Apply uncover up-left effect: @example blend=all_expr='if(gte(T*SH*40+Y,H)*gte((T*40*SW+X)*W/H,W),A,B)' @end example @item Split diagonally video and shows top and bottom layer on each side: @example blend=all_expr='if(gt(X,Y*(W/H)),A,B)' @end example @item Display differences between the current and the previous frame: @example tblend=all_mode=grainextract @end example @end itemize @section boxblur Apply a boxblur algorithm to the input video. It accepts the following parameters: @table @option @item luma_radius, lr @item luma_power, lp @item chroma_radius, cr @item chroma_power, cp @item alpha_radius, ar @item alpha_power, ap @end table A description of the accepted options follows. @table @option @item luma_radius, lr @item chroma_radius, cr @item alpha_radius, ar Set an expression for the box radius in pixels used for blurring the corresponding input plane. The radius value must be a non-negative number, and must not be greater than the value of the expression @code{min(w,h)/2} for the luma and alpha planes, and of @code{min(cw,ch)/2} for the chroma planes. Default value for @option{luma_radius} is "2". If not specified, @option{chroma_radius} and @option{alpha_radius} default to the corresponding value set for @option{luma_radius}. The expressions can contain the following constants: @table @option @item w @item h The input width and height in pixels. @item cw @item ch The input chroma image width and height in pixels. @item hsub @item vsub The horizontal and vertical chroma subsample values. For example, for the pixel format "yuv422p", @var{hsub} is 2 and @var{vsub} is 1. @end table @item luma_power, lp @item chroma_power, cp @item alpha_power, ap Specify how many times the boxblur filter is applied to the corresponding plane. Default value for @option{luma_power} is 2. If not specified, @option{chroma_power} and @option{alpha_power} default to the corresponding value set for @option{luma_power}. A value of 0 will disable the effect. @end table @subsection Examples @itemize @item Apply a boxblur filter with the luma, chroma, and alpha radii set to 2: @example boxblur=luma_radius=2:luma_power=1 boxblur=2:1 @end example @item Set the luma radius to 2, and alpha and chroma radius to 0: @example boxblur=2:1:cr=0:ar=0 @end example @item Set the luma and chroma radii to a fraction of the video dimension: @example boxblur=luma_radius=min(h\,w)/10:luma_power=1:chroma_radius=min(cw\,ch)/10:chroma_power=1 @end example @end itemize @section bwdif Deinterlace the input video ("bwdif" stands for "Bob Weaver Deinterlacing Filter"). Motion adaptive deinterlacing based on yadif with the use of w3fdif and cubic interpolation algorithms. It accepts the following parameters: @table @option @item mode The interlacing mode to adopt. It accepts one of the following values: @table @option @item 0, send_frame Output one frame for each frame. @item 1, send_field Output one frame for each field. @end table The default value is @code{send_field}. @item parity The picture field parity assumed for the input interlaced video. It accepts one of the following values: @table @option @item 0, tff Assume the top field is first. @item 1, bff Assume the bottom field is first. @item -1, auto Enable automatic detection of field parity. @end table The default value is @code{auto}. If the interlacing is unknown or the decoder does not export this information, top field first will be assumed. @item deint Specify which frames to deinterlace. Accept one of the following values: @table @option @item 0, all Deinterlace all frames. @item 1, interlaced Only deinterlace frames marked as interlaced. @end table The default value is @code{all}. @end table @section chromakey YUV colorspace color/chroma keying. The filter accepts the following options: @table @option @item color The color which will be replaced with transparency. @item similarity Similarity percentage with the key color. 0.01 matches only the exact key color, while 1.0 matches everything. @item blend Blend percentage. 0.0 makes pixels either fully transparent, or not transparent at all. Higher values result in semi-transparent pixels, with a higher transparency the more similar the pixels color is to the key color. @item yuv Signals that the color passed is already in YUV instead of RGB. Literal colors like "green" or "red" don't make sense with this enabled anymore. This can be used to pass exact YUV values as hexadecimal numbers. @end table @subsection Examples @itemize @item Make every green pixel in the input image transparent: @example ffmpeg -i input.png -vf chromakey=green out.png @end example @item Overlay a greenscreen-video on top of a static black background. @example ffmpeg -f lavfi -i color=c=black:s=1280x720 -i video.mp4 -shortest -filter_complex "[1:v]chromakey=0x70de77:0.1:0.2[ckout];[0:v][ckout]overlay[out]" -map "[out]" output.mkv @end example @end itemize @section ciescope Display CIE color diagram with pixels overlaid onto it. The filter accepts the following options: @table @option @item system Set color system. @table @samp @item ntsc, 470m @item ebu, 470bg @item smpte @item 240m @item apple @item widergb @item cie1931 @item rec709, hdtv @item uhdtv, rec2020 @end table @item cie Set CIE system. @table @samp @item xyy @item ucs @item luv @end table @item gamuts Set what gamuts to draw. See @code{system} option for available values. @item size, s Set ciescope size, by default set to 512. @item intensity, i Set intensity used to map input pixel values to CIE diagram. @item contrast Set contrast used to draw tongue colors that are out of active color system gamut. @item corrgamma Correct gamma displayed on scope, by default enabled. @item showwhite Show white point on CIE diagram, by default disabled. @item gamma Set input gamma. Used only with XYZ input color space. @end table @section codecview Visualize information exported by some codecs. Some codecs can export information through frames using side-data or other means. For example, some MPEG based codecs export motion vectors through the @var{export_mvs} flag in the codec @option{flags2} option. The filter accepts the following option: @table @option @item mv Set motion vectors to visualize. Available flags for @var{mv} are: @table @samp @item pf forward predicted MVs of P-frames @item bf forward predicted MVs of B-frames @item bb backward predicted MVs of B-frames @end table @item qp Display quantization parameters using the chroma planes. @item mv_type, mvt Set motion vectors type to visualize. Includes MVs from all frames unless specified by @var{frame_type} option. Available flags for @var{mv_type} are: @table @samp @item fp forward predicted MVs @item bp backward predicted MVs @end table @item frame_type, ft Set frame type to visualize motion vectors of. Available flags for @var{frame_type} are: @table @samp @item if intra-coded frames (I-frames) @item pf predicted frames (P-frames) @item bf bi-directionally predicted frames (B-frames) @end table @end table @subsection Examples @itemize @item Visualize forward predicted MVs of all frames using @command{ffplay}: @example ffplay -flags2 +export_mvs input.mp4 -vf codecview=mv_type=fp @end example @item Visualize multi-directionals MVs of P and B-Frames using @command{ffplay}: @example ffplay -flags2 +export_mvs input.mp4 -vf codecview=mv=pf+bf+bb @end example @end itemize @section colorbalance Modify intensity of primary colors (red, green and blue) of input frames. The filter allows an input frame to be adjusted in the shadows, midtones or highlights regions for the red-cyan, green-magenta or blue-yellow balance. A positive adjustment value shifts the balance towards the primary color, a negative value towards the complementary color. The filter accepts the following options: @table @option @item rs @item gs @item bs Adjust red, green and blue shadows (darkest pixels). @item rm @item gm @item bm Adjust red, green and blue midtones (medium pixels). @item rh @item gh @item bh Adjust red, green and blue highlights (brightest pixels). Allowed ranges for options are @code{[-1.0, 1.0]}. Defaults are @code{0}. @end table @subsection Examples @itemize @item Add red color cast to shadows: @example colorbalance=rs=.3 @end example @end itemize @section colorkey RGB colorspace color keying. The filter accepts the following options: @table @option @item color The color which will be replaced with transparency. @item similarity Similarity percentage with the key color. 0.01 matches only the exact key color, while 1.0 matches everything. @item blend Blend percentage. 0.0 makes pixels either fully transparent, or not transparent at all. Higher values result in semi-transparent pixels, with a higher transparency the more similar the pixels color is to the key color. @end table @subsection Examples @itemize @item Make every green pixel in the input image transparent: @example ffmpeg -i input.png -vf colorkey=green out.png @end example @item Overlay a greenscreen-video on top of a static background image. @example ffmpeg -i background.png -i video.mp4 -filter_complex "[1:v]colorkey=0x3BBD1E:0.3:0.2[ckout];[0:v][ckout]overlay[out]" -map "[out]" output.flv @end example @end itemize @section colorlevels Adjust video input frames using levels. The filter accepts the following options: @table @option @item rimin @item gimin @item bimin @item aimin Adjust red, green, blue and alpha input black point. Allowed ranges for options are @code{[-1.0, 1.0]}. Defaults are @code{0}. @item rimax @item gimax @item bimax @item aimax Adjust red, green, blue and alpha input white point. Allowed ranges for options are @code{[-1.0, 1.0]}. Defaults are @code{1}. Input levels are used to lighten highlights (bright tones), darken shadows (dark tones), change the balance of bright and dark tones. @item romin @item gomin @item bomin @item aomin Adjust red, green, blue and alpha output black point. Allowed ranges for options are @code{[0, 1.0]}. Defaults are @code{0}. @item romax @item gomax @item bomax @item aomax Adjust red, green, blue and alpha output white point. Allowed ranges for options are @code{[0, 1.0]}. Defaults are @code{1}. Output levels allows manual selection of a constrained output level range. @end table @subsection Examples @itemize @item Make video output darker: @example colorlevels=rimin=0.058:gimin=0.058:bimin=0.058 @end example @item Increase contrast: @example colorlevels=rimin=0.039:gimin=0.039:bimin=0.039:rimax=0.96:gimax=0.96:bimax=0.96 @end example @item Make video output lighter: @example colorlevels=rimax=0.902:gimax=0.902:bimax=0.902 @end example @item Increase brightness: @example colorlevels=romin=0.5:gomin=0.5:bomin=0.5 @end example @end itemize @section colorchannelmixer Adjust video input frames by re-mixing color channels. This filter modifies a color channel by adding the values associated to the other channels of the same pixels. For example if the value to modify is red, the output value will be: @example @var{red}=@var{red}*@var{rr} + @var{blue}*@var{rb} + @var{green}*@var{rg} + @var{alpha}*@var{ra} @end example The filter accepts the following options: @table @option @item rr @item rg @item rb @item ra Adjust contribution of input red, green, blue and alpha channels for output red channel. Default is @code{1} for @var{rr}, and @code{0} for @var{rg}, @var{rb} and @var{ra}. @item gr @item gg @item gb @item ga Adjust contribution of input red, green, blue and alpha channels for output green channel. Default is @code{1} for @var{gg}, and @code{0} for @var{gr}, @var{gb} and @var{ga}. @item br @item bg @item bb @item ba Adjust contribution of input red, green, blue and alpha channels for output blue channel. Default is @code{1} for @var{bb}, and @code{0} for @var{br}, @var{bg} and @var{ba}. @item ar @item ag @item ab @item aa Adjust contribution of input red, green, blue and alpha channels for output alpha channel. Default is @code{1} for @var{aa}, and @code{0} for @var{ar}, @var{ag} and @var{ab}. Allowed ranges for options are @code{[-2.0, 2.0]}. @end table @subsection Examples @itemize @item Convert source to grayscale: @example colorchannelmixer=.3:.4:.3:0:.3:.4:.3:0:.3:.4:.3 @end example @item Simulate sepia tones: @example colorchannelmixer=.393:.769:.189:0:.349:.686:.168:0:.272:.534:.131 @end example @end itemize @section colormatrix Convert color matrix. The filter accepts the following options: @table @option @item src @item dst Specify the source and destination color matrix. Both values must be specified. The accepted values are: @table @samp @item bt709 BT.709 @item fcc FCC @item bt601 BT.601 @item bt470 BT.470 @item bt470bg BT.470BG @item smpte170m SMPTE-170M @item smpte240m SMPTE-240M @item bt2020 BT.2020 @end table @end table For example to convert from BT.601 to SMPTE-240M, use the command: @example colormatrix=bt601:smpte240m @end example @section colorspace Convert colorspace, transfer characteristics or color primaries. Input video needs to have an even size. The filter accepts the following options: @table @option @anchor{all} @item all Specify all color properties at once. The accepted values are: @table @samp @item bt470m BT.470M @item bt470bg BT.470BG @item bt601-6-525 BT.601-6 525 @item bt601-6-625 BT.601-6 625 @item bt709 BT.709 @item smpte170m SMPTE-170M @item smpte240m SMPTE-240M @item bt2020 BT.2020 @end table @anchor{space} @item space Specify output colorspace. The accepted values are: @table @samp @item bt709 BT.709 @item fcc FCC @item bt470bg BT.470BG or BT.601-6 625 @item smpte170m SMPTE-170M or BT.601-6 525 @item smpte240m SMPTE-240M @item ycgco YCgCo @item bt2020ncl BT.2020 with non-constant luminance @end table @anchor{trc} @item trc Specify output transfer characteristics. The accepted values are: @table @samp @item bt709 BT.709 @item bt470m BT.470M @item bt470bg BT.470BG @item gamma22 Constant gamma of 2.2 @item gamma28 Constant gamma of 2.8 @item smpte170m SMPTE-170M, BT.601-6 625 or BT.601-6 525 @item smpte240m SMPTE-240M @item srgb SRGB @item iec61966-2-1 iec61966-2-1 @item iec61966-2-4 iec61966-2-4 @item xvycc xvycc @item bt2020-10 BT.2020 for 10-bits content @item bt2020-12 BT.2020 for 12-bits content @end table @anchor{primaries} @item primaries Specify output color primaries. The accepted values are: @table @samp @item bt709 BT.709 @item bt470m BT.470M @item bt470bg BT.470BG or BT.601-6 625 @item smpte170m SMPTE-170M or BT.601-6 525 @item smpte240m SMPTE-240M @item film film @item smpte431 SMPTE-431 @item smpte432 SMPTE-432 @item bt2020 BT.2020 @item jedec-p22 JEDEC P22 phosphors @end table @anchor{range} @item range Specify output color range. The accepted values are: @table @samp @item tv TV (restricted) range @item mpeg MPEG (restricted) range @item pc PC (full) range @item jpeg JPEG (full) range @end table @item format Specify output color format. The accepted values are: @table @samp @item yuv420p YUV 4:2:0 planar 8-bits @item yuv420p10 YUV 4:2:0 planar 10-bits @item yuv420p12 YUV 4:2:0 planar 12-bits @item yuv422p YUV 4:2:2 planar 8-bits @item yuv422p10 YUV 4:2:2 planar 10-bits @item yuv422p12 YUV 4:2:2 planar 12-bits @item yuv444p YUV 4:4:4 planar 8-bits @item yuv444p10 YUV 4:4:4 planar 10-bits @item yuv444p12 YUV 4:4:4 planar 12-bits @end table @item fast Do a fast conversion, which skips gamma/primary correction. This will take significantly less CPU, but will be mathematically incorrect. To get output compatible with that produced by the colormatrix filter, use fast=1. @item dither Specify dithering mode. The accepted values are: @table @samp @item none No dithering @item fsb Floyd-Steinberg dithering @end table @item wpadapt Whitepoint adaptation mode. The accepted values are: @table @samp @item bradford Bradford whitepoint adaptation @item vonkries von Kries whitepoint adaptation @item identity identity whitepoint adaptation (i.e. no whitepoint adaptation) @end table @item iall Override all input properties at once. Same accepted values as @ref{all}. @item ispace Override input colorspace. Same accepted values as @ref{space}. @item iprimaries Override input color primaries. Same accepted values as @ref{primaries}. @item itrc Override input transfer characteristics. Same accepted values as @ref{trc}. @item irange Override input color range. Same accepted values as @ref{range}. @end table The filter converts the transfer characteristics, color space and color primaries to the specified user values. The output value, if not specified, is set to a default value based on the "all" property. If that property is also not specified, the filter will log an error. The output color range and format default to the same value as the input color range and format. The input transfer characteristics, color space, color primaries and color range should be set on the input data. If any of these are missing, the filter will log an error and no conversion will take place. For example to convert the input to SMPTE-240M, use the command: @example colorspace=smpte240m @end example @section convolution Apply convolution 3x3, 5x5 or 7x7 filter. The filter accepts the following options: @table @option @item 0m @item 1m @item 2m @item 3m Set matrix for each plane. Matrix is sequence of 9, 25 or 49 signed integers. @item 0rdiv @item 1rdiv @item 2rdiv @item 3rdiv Set multiplier for calculated value for each plane. @item 0bias @item 1bias @item 2bias @item 3bias Set bias for each plane. This value is added to the result of the multiplication. Useful for making the overall image brighter or darker. Default is 0.0. @end table @subsection Examples @itemize @item Apply sharpen: @example convolution="0 -1 0 -1 5 -1 0 -1 0:0 -1 0 -1 5 -1 0 -1 0:0 -1 0 -1 5 -1 0 -1 0:0 -1 0 -1 5 -1 0 -1 0" @end example @item Apply blur: @example convolution="1 1 1 1 1 1 1 1 1:1 1 1 1 1 1 1 1 1:1 1 1 1 1 1 1 1 1:1 1 1 1 1 1 1 1 1:1/9:1/9:1/9:1/9" @end example @item Apply edge enhance: @example convolution="0 0 0 -1 1 0 0 0 0:0 0 0 -1 1 0 0 0 0:0 0 0 -1 1 0 0 0 0:0 0 0 -1 1 0 0 0 0:5:1:1:1:0:128:128:128" @end example @item Apply edge detect: @example convolution="0 1 0 1 -4 1 0 1 0:0 1 0 1 -4 1 0 1 0:0 1 0 1 -4 1 0 1 0:0 1 0 1 -4 1 0 1 0:5:5:5:1:0:128:128:128" @end example @item Apply laplacian edge detector which includes diagonals: @example convolution="1 1 1 1 -8 1 1 1 1:1 1 1 1 -8 1 1 1 1:1 1 1 1 -8 1 1 1 1:1 1 1 1 -8 1 1 1 1:5:5:5:1:0:128:128:0" @end example @item Apply emboss: @example convolution="-2 -1 0 -1 1 1 0 1 2:-2 -1 0 -1 1 1 0 1 2:-2 -1 0 -1 1 1 0 1 2:-2 -1 0 -1 1 1 0 1 2" @end example @end itemize @section convolve Apply 2D convolution of video stream in frequency domain using second stream as impulse. The filter accepts the following options: @table @option @item planes Set which planes to process. @item impulse Set which impulse video frames will be processed, can be @var{first} or @var{all}. Default is @var{all}. @end table The @code{convolve} filter also supports the @ref{framesync} options. @section copy Copy the input video source unchanged to the output. This is mainly useful for testing purposes. @anchor{coreimage} @section coreimage Video filtering on GPU using Apple's CoreImage API on OSX. Hardware acceleration is based on an OpenGL context. Usually, this means it is processed by video hardware. However, software-based OpenGL implementations exist which means there is no guarantee for hardware processing. It depends on the respective OSX. There are many filters and image generators provided by Apple that come with a large variety of options. The filter has to be referenced by its name along with its options. The coreimage filter accepts the following options: @table @option @item list_filters List all available filters and generators along with all their respective options as well as possible minimum and maximum values along with the default values. @example list_filters=true @end example @item filter Specify all filters by their respective name and options. Use @var{list_filters} to determine all valid filter names and options. Numerical options are specified by a float value and are automatically clamped to their respective value range. Vector and color options have to be specified by a list of space separated float values. Character escaping has to be done. A special option name @code{default} is available to use default options for a filter. It is required to specify either @code{default} or at least one of the filter options. All omitted options are used with their default values. The syntax of the filter string is as follows: @example filter=@@