1 \input texinfo @c -*- texinfo -*-
3 @settitle Libavfilter Documentation
5 @center @titlefont{Libavfilter Documentation}
14 Libavfilter is the filtering API of FFmpeg. It is the substitute of the
15 now deprecated 'vhooks' and started as a Google Summer of Code project.
17 Audio filtering integration into the main FFmpeg repository is a work in
18 progress, so audio API and ABI should not be considered stable yet.
22 In libavfilter, it is possible for filters to have multiple inputs and
24 To illustrate the sorts of things that are possible, we can
25 use a complex filter graph. For example, the following one:
28 input --> split --> fifo -----------------------> overlay --> output
31 +------> fifo --> crop --> vflip --------+
34 splits the stream in two streams, sends one stream through the crop filter
35 and the vflip filter before merging it back with the other stream by
36 overlaying it on top. You can use the following command to achieve this:
39 ./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]
42 where input_video.avi has a vertical resolution of 480 pixels. The
43 result will be that in output the top half of the video is mirrored
46 Video filters are loaded using the @var{-vf} option passed to
47 ffmpeg or to ffplay. Filters in the same linear chain are separated by
48 commas. In our example, @var{split, fifo, overlay} are in one linear
49 chain, and @var{fifo, crop, vflip} are in another. The points where
50 the linear chains join are labeled by names enclosed in square
51 brackets. In our example, that is @var{[T1]} and @var{[T2]}. The magic
52 labels @var{[in]} and @var{[out]} are the points where video is input
55 Some filters take in input a list of parameters: they are specified
56 after the filter name and an equal sign, and are separated each other
59 There exist so-called @var{source filters} that do not have a video
60 input, and we expect in the future some @var{sink filters} that will
61 not have video output.
65 The @file{graph2dot} program included in the FFmpeg @file{tools}
66 directory can be used to parse a filter graph description and issue a
67 corresponding textual representation in the dot language.
74 to see how to use @file{graph2dot}.
76 You can then pass the dot description to the @file{dot} program (from
77 the graphviz suite of programs) and obtain a graphical representation
80 For example the sequence of commands:
82 echo @var{GRAPH_DESCRIPTION} | \
83 tools/graph2dot -o graph.tmp && \
84 dot -Tpng graph.tmp -o graph.png && \
88 can be used to create and display an image representing the graph
89 described by the @var{GRAPH_DESCRIPTION} string.