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- \input texinfo @c -*- texinfo -*-
- @settitle Libavfilter Documentation
- @titlepage
- @center @titlefont{Libavfilter Documentation}
- @end titlepage
- @top
- @contents
- @chapter Introduction
- Libavfilter is the filtering API of FFmpeg. It is the substitute of the
- now deprecated 'vhooks' and started as a Google Summer of Code project.
- Audio filtering integration into the main FFmpeg repository is a work in
- progress, so audio API and ABI should not be considered stable yet.
- @chapter Tutorial
- In libavfilter, it is possible for filters to have multiple inputs and
- multiple outputs.
- To illustrate the sorts of things that are possible, we can
- use a complex filter graph. For example, the following one:
- @example
- input --> split --> fifo -----------------------> overlay --> output
- | ^
- | |
- +------> fifo --> crop --> vflip --------+
- @end example
- splits the stream in two streams, 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 "[in] split [T1], fifo, [T2] overlay=0:H/2 [out]; [T1] fifo, crop=iw:ih/2:0:ih/2, vflip [T2]" output
- @end example
- The result will be that in output the top half of the video is mirrored
- onto the bottom half.
- Video filters are loaded using the @var{-vf} option passed to
- ffmpeg or to ffplay. Filters in the same linear chain are separated by
- commas. In our example, @var{split, fifo, overlay} are in one linear
- chain, and @var{fifo, crop, vflip} are in another. The points where
- the linear chains join are labeled by names enclosed in square
- brackets. In our example, that is @var{[T1]} and @var{[T2]}. The magic
- labels @var{[in]} and @var{[out]} are the points where video is input
- and output.
- Some filters take in input a list of parameters: they are specified
- after the filter name and an equal sign, and are separated each other
- by a semicolon.
- There exist so-called @var{source filters} that do not have a video
- input, and we expect in the future some @var{sink filters} that will
- not have video output.
- @chapter graph2dot
- The @file{graph2dot} program included in the FFmpeg @file{tools}
- directory can be used to parse a filter graph 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 filter graph.
- 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.
- @include filters.texi
- @bye
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