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93 lines
3.0 KiB
93 lines
3.0 KiB
\input texinfo @c -*- texinfo -*- |
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@settitle Libavfilter Documentation |
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@titlepage |
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@center @titlefont{Libavfilter Documentation} |
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@end titlepage |
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@top |
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@contents |
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@chapter Introduction |
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Libavfilter is the filtering API of FFmpeg. It is the substitute of the |
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now deprecated 'vhooks' and started as a Google Summer of Code project. |
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Audio filtering integration into the main FFmpeg repository is a work in |
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progress, so audio API and ABI should not be considered stable yet. |
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@chapter Tutorial |
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In libavfilter, it is possible for filters to have multiple inputs and |
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multiple outputs. |
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To illustrate the sorts of things that are possible, we can |
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use a complex filter graph. For example, the following one: |
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@example |
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input --> split --> fifo -----------------------> overlay --> output |
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+------> fifo --> crop --> vflip --------+ |
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@end example |
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splits the stream in two streams, sends one stream through the crop filter |
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and the vflip filter before merging it back with the other stream by |
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overlaying it on top. You can use the following command to achieve this: |
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@example |
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./ffmpeg -i in.avi -s 240x320 -vf "[in] split [T1], fifo, [T2] overlay= 0:240 [out]; [T1] fifo, crop=0:0:-1:240, vflip [T2] |
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@end example |
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where input_video.avi has a vertical resolution of 480 pixels. The |
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result will be that in output the top half of the video is mirrored |
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onto the bottom half. |
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Video filters are loaded using the @var{-vf} option passed to |
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ffmpeg or to ffplay. Filters in the same linear chain are separated by |
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commas. In our example, @var{split, fifo, overlay} are in one linear |
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chain, and @var{fifo, crop, vflip} are in another. The points where |
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the linear chains join are labeled by names enclosed in square |
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brackets. In our example, that is @var{[T1]} and @var{[T2]}. The magic |
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labels @var{[in]} and @var{[out]} are the points where video is input |
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and output. |
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Some filters take in input a list of parameters: they are specified |
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after the filter name and an equal sign, and are separated each other |
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by a semicolon. |
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There exist so-called @var{source filters} that do not have a video |
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input, and we expect in the future some @var{sink filters} that will |
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not have video output. |
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@chapter graph2dot |
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The @file{graph2dot} program included in the FFmpeg @file{tools} |
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directory can be used to parse a filter graph description and issue a |
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corresponding textual representation in the dot language. |
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Invoke the command: |
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@example |
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graph2dot -h |
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@end example |
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to see how to use @file{graph2dot}. |
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You can then pass the dot description to the @file{dot} program (from |
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the graphviz suite of programs) and obtain a graphical representation |
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of the filter graph. |
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For example the sequence of commands: |
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@example |
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echo @var{GRAPH_DESCRIPTION} | \ |
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tools/graph2dot -o graph.tmp && \ |
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dot -Tpng graph.tmp -o graph.png && \ |
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display graph.png |
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@end example |
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can be used to create and display an image representing the graph |
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described by the @var{GRAPH_DESCRIPTION} string. |
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@include filters.texi |
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@bye
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