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lavf: add some basic documentation of the muxing process

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Anton Khirnov 2014-02-04 17:35:18 +01:00
parent 4c75059950
commit 54f7e79d47
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libavformat/avformat.h
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@ -173,6 +173,58 @@
*
* @defgroup lavf_encoding Muxing
* @{
* Muxers take encoded data in the form of @ref AVPacket "AVPackets" and write
* it into files or other output bytestreams in the specified container format.
*
* The main API functions for muxing are avformat_write_header() for writing the
* file header, av_write_frame() / av_interleaved_write_frame() for writing the
* packets and av_write_trailer() for finalizing the file.
*
* At the beginning of the muxing process, the caller must first call
* avformat_alloc_context() to create a muxing context. The caller then sets up
* the muxer by filling the various fields in this context:
*
* - The @ref AVFormatContext.oformat "oformat" field must be set to select the
* muxer that will be used.
* - Unless the format is of the AVFMT_NOFILE type, the @ref AVFormatContext.pb
* "pb" field must be set to an opened IO context, either returned from
* avio_open2() or a custom one.
* - Unless the format is of the AVFMT_NOSTREAMS type, at least one stream must
* be created with the avformat_new_stream() function. The caller should fill
* the @ref AVStream.codec "stream codec context" information, such as the
* codec @ref AVCodecContext.codec_type "type", @ref AVCodecContext.codec_id
* "id" and other parameters (e.g. width / height, the pixel or sample format,
* etc.) as known. The @ref AVCodecContext.time_base "codec timebase" should
* be set to the timebase that the caller desires to use for this stream (note
* that the timebase actually used by the muxer can be different, as will be
* described later).
* - The caller may fill in additional information, such as @ref
* AVFormatContext.metadata "global" or @ref AVStream.metadata "per-stream"
* metadata, @ref AVFormatContext.chapters "chapters", @ref
* AVFormatContext.programs "programs", etc. as described in the
* AVFormatContext documentation. Whether such information will actually be
* stored in the output depends on what the container format and the muxer
* support.
*
* When the muxing context is fully set up, the caller must call
* avformat_write_header() to initialize the muxer internals and write the file
* header. Whether anything actually is written to the IO context at this step
* depends on the muxer, but this function must always be called. Any muxer
* private options must be passed in the options parameter to this function.
*
* The data is then sent to the muxer by repeatedly calling av_write_frame() or
* av_interleaved_write_frame() (consult those functions' documentation for
* discussion on the difference between them; only one of them may be used with
* a single muxing context, they should not be mixed). Do note that the timing
* information on the packets sent to the muxer must be in the corresponding
* AVStream's timebase. That timebase is set by the muxer (in the
* avformat_write_header() step) and may be different from the timebase the
* caller set on the codec context.
*
* Once all the data has been written, the caller must call av_write_trailer()
* to flush any buffered packets and finalize the output file, then close the IO
* context (if any) and finally free the muxing context with
* avformat_free_context().
* @}
*
* @defgroup lavf_io I/O Read/Write