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Make Audio Encoders a separate chapter, and decrese the contained sections level by one. Improve rendering, and improve consistency with the other parts of the manual.
373 lines
11 KiB
Plaintext
373 lines
11 KiB
Plaintext
@chapter Encoders
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@c man begin ENCODERS
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Encoders are configured elements in FFmpeg which allow the encoding of
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multimedia streams.
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When you configure your FFmpeg build, all the supported native encoders
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are enabled by default. Encoders requiring an external library must be enabled
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manually via the corresponding @code{--enable-lib} option. You can list all
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available encoders using the configure option @code{--list-encoders}.
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You can disable all the encoders with the configure option
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@code{--disable-encoders} and selectively enable / disable single encoders
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with the options @code{--enable-encoder=@var{ENCODER}} /
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@code{--disable-encoder=@var{ENCODER}}.
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The option @code{-codecs} of the ff* tools will display the list of
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enabled encoders.
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@c man end ENCODERS
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@chapter Audio Encoders
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@c man begin AUDIO ENCODERS
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A description of some of the currently available audio encoders
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follows.
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@section ac3 and ac3_fixed
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AC-3 audio encoders.
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These encoders implement part of ATSC A/52:2010 and ETSI TS 102 366, as well as
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the undocumented RealAudio 3 (a.k.a. dnet).
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The @var{ac3} encoder uses floating-point math, while the @var{ac3_fixed}
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encoder only uses fixed-point integer math. This does not mean that one is
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always faster, just that one or the other may be better suited to a
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particular system. The floating-point encoder will generally produce better
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quality audio for a given bitrate. The @var{ac3_fixed} encoder is not the
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default codec for any of the output formats, so it must be specified explicitly
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using the option @code{-acodec ac3_fixed} in order to use it.
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@subsection AC-3 Metadata
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The AC-3 metadata options are used to set parameters that describe the audio,
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but in most cases do not affect the audio encoding itself. Some of the options
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do directly affect or influence the decoding and playback of the resulting
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bitstream, while others are just for informational purposes. A few of the
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options will add bits to the output stream that could otherwise be used for
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audio data, and will thus affect the quality of the output. Those will be
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indicated accordingly with a note in the option list below.
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These parameters are described in detail in several publicly-available
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documents.
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@itemize
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@item @uref{http://www.atsc.org/cms/standards/a_52-2010.pdf,A/52:2010 - Digital Audio Compression (AC-3) (E-AC-3) Standard}
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@item @uref{http://www.atsc.org/cms/standards/a_54a_with_corr_1.pdf,A/54 - Guide to the Use of the ATSC Digital Television Standard}
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@item @uref{http://www.dolby.com/uploadedFiles/zz-_Shared_Assets/English_PDFs/Professional/18_Metadata.Guide.pdf,Dolby Metadata Guide}
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@item @uref{http://www.dolby.com/uploadedFiles/zz-_Shared_Assets/English_PDFs/Professional/46_DDEncodingGuidelines.pdf,Dolby Digital Professional Encoding Guidelines}
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@end itemize
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@subsubsection Metadata Control Options
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@table @option
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@item -per_frame_metadata @var{boolean}
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Allow Per-Frame Metadata. Specifies if the encoder should check for changing
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metadata for each frame.
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@table @option
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@item 0
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The metadata values set at initialization will be used for every frame in the
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stream. (default)
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@item 1
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Metadata values can be changed before encoding each frame.
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@end table
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@end table
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@subsubsection Downmix Levels
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@table @option
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@item -center_mixlev @var{level}
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Center Mix Level. The amount of gain the decoder should apply to the center
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channel when downmixing to stereo. This field will only be written to the
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bitstream if a center channel is present. The value is specified as a scale
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factor. There are 3 valid values:
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@table @option
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@item 0.707
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Apply -3dB gain
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@item 0.595
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Apply -4.5dB gain (default)
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@item 0.500
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Apply -6dB gain
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@end table
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@item -surround_mixlev @var{level}
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Surround Mix Level. The amount of gain the decoder should apply to the surround
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channel(s) when downmixing to stereo. This field will only be written to the
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bitstream if one or more surround channels are present. The value is specified
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as a scale factor. There are 3 valid values:
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@table @option
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@item 0.707
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Apply -3dB gain
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@item 0.500
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Apply -6dB gain (default)
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@item 0.000
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Silence Surround Channel(s)
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@end table
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@end table
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@subsubsection Audio Production Information
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Audio Production Information is optional information describing the mixing
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environment. Either none or both of the fields are written to the bitstream.
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@table @option
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@item -mixing_level @var{number}
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Mixing Level. Specifies peak sound pressure level (SPL) in the production
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environment when the mix was mastered. Valid values are 80 to 111, or -1 for
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unknown or not indicated. The default value is -1, but that value cannot be
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used if the Audio Production Information is written to the bitstream. Therefore,
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if the @code{room_type} option is not the default value, the @code{mixing_level}
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option must not be -1.
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@item -room_type @var{type}
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Room Type. Describes the equalization used during the final mixing session at
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the studio or on the dubbing stage. A large room is a dubbing stage with the
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industry standard X-curve equalization; a small room has flat equalization.
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This field will not be written to the bitstream if both the @code{mixing_level}
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option and the @code{room_type} option have the default values.
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@table @option
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@item 0
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@itemx notindicated
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Not Indicated (default)
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@item 1
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@itemx large
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Large Room
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@item 2
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@itemx small
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Small Room
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@end table
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@end table
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@subsubsection Other Metadata Options
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@table @option
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@item -copyright @var{boolean}
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Copyright Indicator. Specifies whether a copyright exists for this audio.
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@table @option
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@item 0
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@itemx off
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No Copyright Exists (default)
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@item 1
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@itemx on
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Copyright Exists
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@end table
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@item -dialnorm @var{value}
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Dialogue Normalization. Indicates how far the average dialogue level of the
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program is below digital 100% full scale (0 dBFS). This parameter determines a
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level shift during audio reproduction that sets the average volume of the
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dialogue to a preset level. The goal is to match volume level between program
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sources. A value of -31dB will result in no volume level change, relative to
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the source volume, during audio reproduction. Valid values are whole numbers in
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the range -31 to -1, with -31 being the default.
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@item -dsur_mode @var{mode}
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Dolby Surround Mode. Specifies whether the stereo signal uses Dolby Surround
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(Pro Logic). This field will only be written to the bitstream if the audio
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stream is stereo. Using this option does @b{NOT} mean the encoder will actually
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apply Dolby Surround processing.
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@table @option
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@item 0
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@itemx notindicated
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Not Indicated (default)
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@item 1
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@itemx off
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Not Dolby Surround Encoded
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@item 2
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@itemx on
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Dolby Surround Encoded
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@end table
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@item -original @var{boolean}
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Original Bit Stream Indicator. Specifies whether this audio is from the
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original source and not a copy.
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@table @option
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@item 0
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@itemx off
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Not Original Source
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@item 1
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@itemx on
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Original Source (default)
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@end table
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@end table
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@subsection Extended Bitstream Information
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The extended bitstream options are part of the Alternate Bit Stream Syntax as
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specified in Annex D of the A/52:2010 standard. It is grouped into 2 parts.
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If any one parameter in a group is specified, all values in that group will be
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written to the bitstream. Default values are used for those that are written
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but have not been specified. If the mixing levels are written, the decoder
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will use these values instead of the ones specified in the @code{center_mixlev}
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and @code{surround_mixlev} options if it supports the Alternate Bit Stream
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Syntax.
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@subsubsection Extended Bitstream Information - Part 1
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@table @option
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@item -dmix_mode @var{mode}
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Preferred Stereo Downmix Mode. Allows the user to select either Lt/Rt
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(Dolby Surround) or Lo/Ro (normal stereo) as the preferred stereo downmix mode.
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@table @option
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@item 0
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@itemx notindicated
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Not Indicated (default)
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@item 1
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@itemx ltrt
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Lt/Rt Downmix Preferred
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@item 2
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@itemx loro
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Lo/Ro Downmix Preferred
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@end table
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@item -ltrt_cmixlev @var{level}
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Lt/Rt Center Mix Level. The amount of gain the decoder should apply to the
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center channel when downmixing to stereo in Lt/Rt mode.
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@table @option
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@item 1.414
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Apply +3dB gain
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@item 1.189
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Apply +1.5dB gain
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@item 1.000
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Apply 0dB gain
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@item 0.841
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Apply -1.5dB gain
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@item 0.707
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Apply -3.0dB gain
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@item 0.595
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Apply -4.5dB gain (default)
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@item 0.500
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Apply -6.0dB gain
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@item 0.000
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Silence Center Channel
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@end table
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@item -ltrt_surmixlev @var{level}
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Lt/Rt Surround Mix Level. The amount of gain the decoder should apply to the
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surround channel(s) when downmixing to stereo in Lt/Rt mode.
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@table @option
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@item 0.841
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Apply -1.5dB gain
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@item 0.707
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Apply -3.0dB gain
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@item 0.595
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Apply -4.5dB gain
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@item 0.500
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Apply -6.0dB gain (default)
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@item 0.000
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Silence Surround Channel(s)
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@end table
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@item -loro_cmixlev @var{level}
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Lo/Ro Center Mix Level. The amount of gain the decoder should apply to the
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center channel when downmixing to stereo in Lo/Ro mode.
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@table @option
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@item 1.414
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Apply +3dB gain
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@item 1.189
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Apply +1.5dB gain
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@item 1.000
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Apply 0dB gain
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@item 0.841
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Apply -1.5dB gain
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@item 0.707
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Apply -3.0dB gain
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@item 0.595
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Apply -4.5dB gain (default)
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@item 0.500
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Apply -6.0dB gain
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@item 0.000
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Silence Center Channel
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@end table
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@item -loro_surmixlev @var{level}
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Lo/Ro Surround Mix Level. The amount of gain the decoder should apply to the
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surround channel(s) when downmixing to stereo in Lo/Ro mode.
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@table @option
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@item 0.841
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Apply -1.5dB gain
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@item 0.707
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Apply -3.0dB gain
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@item 0.595
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Apply -4.5dB gain
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@item 0.500
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Apply -6.0dB gain (default)
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@item 0.000
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Silence Surround Channel(s)
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@end table
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@end table
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@subsubsection Extended Bitstream Information - Part 2
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@table @option
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@item -dsurex_mode @var{mode}
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Dolby Surround EX Mode. Indicates whether the stream uses Dolby Surround EX
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(7.1 matrixed to 5.1). Using this option does @b{NOT} mean the encoder will actually
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apply Dolby Surround EX processing.
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@table @option
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@item 0
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@itemx notindicated
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Not Indicated (default)
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@item 1
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@itemx on
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Dolby Surround EX On
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@item 2
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@itemx off
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Dolby Surround EX Off
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@end table
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@item -dheadphone_mode @var{mode}
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Dolby Headphone Mode. Indicates whether the stream uses Dolby Headphone
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encoding (multi-channel matrixed to 2.0 for use with headphones). Using this
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option does @b{NOT} mean the encoder will actually apply Dolby Headphone
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processing.
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@table @option
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@item 0
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@itemx notindicated
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Not Indicated (default)
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@item 1
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@itemx on
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Dolby Headphone On
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@item 2
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@itemx off
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Dolby Headphone Off
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@end table
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@item -ad_conv_type @var{type}
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A/D Converter Type. Indicates whether the audio has passed through HDCD A/D
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conversion.
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@table @option
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@item 0
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@itemx standard
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Standard A/D Converter (default)
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@item 1
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@itemx hdcd
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HDCD A/D Converter
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@end table
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@end table
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@subsection Other AC-3 Encoding Options
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@table @option
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@item -stereo_rematrixing @var{boolean}
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Stereo Rematrixing. Enables/Disables use of rematrixing for stereo input. This
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is an optional AC-3 feature that increases quality by selectively encoding
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the left/right channels as mid/side. This option is enabled by default, and it
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is highly recommended that it be left as enabled except for testing purposes.
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@end table
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@c man end AUDIO ENCODERS
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