doc/muxers: tee muxer - rearrange, add notes and general tidy-up
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Gyan Doshi
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@ -2037,20 +2037,35 @@ ffmpeg -re -i ... -c:v libx264 -c:a aac -f fifo -fifo_format flv -map 0:v -map 0
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@anchor{tee}
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@section tee
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The tee muxer can be used to write the same data to several files or any
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other kind of muxer. It can be used, for example, to both stream a video to
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the network and save it to disk at the same time.
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The tee muxer can be used to write the same data to several outputs, such as files or streams.
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It can be used, for example, to stream a video over a network and save it to disk at the same time.
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It is different from specifying several outputs to the @command{ffmpeg}
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command-line tool because the audio and video data will be encoded only once
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with the tee muxer; encoding can be a very expensive process. It is not
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useful when using the libavformat API directly because it is then possible
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to feed the same packets to several muxers directly.
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command-line tool. With the tee muxer, the audio and video data will be encoded only once.
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With conventional multiple outputs, multiple encoding operations in parallel are initiated,
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which can be a very expensive process. The tee muxer is not useful when using the libavformat API
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directly because it is then possible to feed the same packets to several muxers directly.
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Since the tee muxer does not represent any particular output format, ffmpeg cannot auto-select
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output streams. So all streams intended for output must be specified using @code{-map}. See
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the examples below.
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Some encoders may need different options depending on the output format;
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the auto-detection of this can not work with the tee muxer, so they need to be explicitly specified.
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The main example is the @option{global_header} flag.
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The slave outputs are specified in the file name given to the muxer,
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separated by '|'. If any of the slave name contains the '|' separator,
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leading or trailing spaces or any special character, those must be
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escaped (see @ref{quoting_and_escaping,,the "Quoting and escaping"
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section in the ffmpeg-utils(1) manual,ffmpeg-utils}).
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@subsection Options
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@table @option
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@item use_fifo @var{bool}
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If set to 1, slave outputs will be processed in separate thread using @ref{fifo}
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If set to 1, slave outputs will be processed in separate threads using the @ref{fifo}
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muxer. This allows to compensate for different speed/latency/reliability of
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outputs and setup transparent recovery. By default this feature is turned off.
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@ -2059,12 +2074,6 @@ Options to pass to fifo pseudo-muxer instances. See @ref{fifo}.
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@end table
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The slave outputs are specified in the file name given to the muxer,
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separated by '|'. If any of the slave name contains the '|' separator,
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leading or trailing spaces or any special character, it must be
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escaped (see @ref{quoting_and_escaping,,the "Quoting and escaping"
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section in the ffmpeg-utils(1) manual,ffmpeg-utils}).
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Muxer options can be specified for each slave by prepending them as a list of
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@var{key}=@var{value} pairs separated by ':', between square brackets. If
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the options values contain a special character or the ':' separator, they
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@ -2073,13 +2082,27 @@ must be escaped; note that this is a second level escaping.
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The following special options are also recognized:
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@table @option
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@item f
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Specify the format name. Useful if it cannot be guessed from the
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output name suffix.
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Specify the format name. Required if it cannot be guessed from the
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output URL.
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@item bsfs[/@var{spec}]
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Specify a list of bitstream filters to apply to the specified
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output.
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It is possible to specify to which streams a given bitstream filter
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applies, by appending a stream specifier to the option separated by
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@code{/}. @var{spec} must be a stream specifier (see @ref{Format
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stream specifiers}).
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If the stream specifier is not specified, the bitstream filters will be
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applied to all streams in the output. This will cause that output operation
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to fail if the output contains streams to which the bitstream filter cannot
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be applied e.g. @code{h264_mp4toannexb} being applied to an output containing an audio stream.
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Options for a bitstream filter must be specified in the form of @code{opt=value}.
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Several bitstream filters can be specified, separated by ",".
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@item use_fifo @var{bool}
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This allows to override tee muxer use_fifo option for individual slave muxer.
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@ -2087,19 +2110,13 @@ This allows to override tee muxer use_fifo option for individual slave muxer.
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This allows to override tee muxer fifo_options for individual slave muxer.
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See @ref{fifo}.
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It is possible to specify to which streams a given bitstream filter
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applies, by appending a stream specifier to the option separated by
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@code{/}. @var{spec} must be a stream specifier (see @ref{Format
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stream specifiers}). If the stream specifier is not specified, the
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bitstream filters will be applied to all streams in the output.
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Several bitstream filters can be specified, separated by ",".
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@item select
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Select the streams that should be mapped to the slave output,
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specified by a stream specifier. If not specified, this defaults to
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all the input streams. You may use multiple stream specifiers
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separated by commas (@code{,}) e.g.: @code{a:0,v}
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all the mapped streams. This will cause that output operation to fail
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if the output format does not accept all mapped streams.
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You may use multiple stream specifiers separated by commas (@code{,}) e.g.: @code{a:0,v}
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@item onfail
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Specify behaviour on output failure. This can be set to either @code{abort} (which is
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@ -2113,7 +2130,7 @@ will continue without being affected.
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@itemize
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@item
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Encode something and both archive it in a WebM file and stream it
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as MPEG-TS over UDP (the streams need to be explicitly mapped):
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as MPEG-TS over UDP:
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@example
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ffmpeg -i ... -c:v libx264 -c:a mp2 -f tee -map 0:v -map 0:a
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"archive-20121107.mkv|[f=mpegts]udp://10.0.1.255:1234/"
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@ -2136,23 +2153,19 @@ option is applied to @file{out.aac} in order to make it contain only
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audio packets.
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@example
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ffmpeg -i ... -map 0 -flags +global_header -c:v libx264 -c:a aac
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-f tee "[bsfs/v=dump_extra]out.ts|[movflags=+faststart]out.mp4|[select=a]out.aac"
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-f tee "[bsfs/v=dump_extra=freq=keyframe]out.ts|[movflags=+faststart]out.mp4|[select=a]out.aac"
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@end example
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@item
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As below, but select only stream @code{a:1} for the audio output. Note
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As above, but select only stream @code{a:1} for the audio output. Note
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that a second level escaping must be performed, as ":" is a special
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character used to separate options.
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@example
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ffmpeg -i ... -map 0 -flags +global_header -c:v libx264 -c:a aac
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-f tee "[bsfs/v=dump_extra]out.ts|[movflags=+faststart]out.mp4|[select=\'a:1\']out.aac"
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-f tee "[bsfs/v=dump_extra=freq=keyframe]out.ts|[movflags=+faststart]out.mp4|[select=\'a:1\']out.aac"
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@end example
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@end itemize
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Note: some codecs may need different options depending on the output format;
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the auto-detection of this can not work with the tee muxer. The main example
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is the @option{global_header} flag.
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@section webm_dash_manifest
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WebM DASH Manifest muxer.
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