\input texinfo @c -*- texinfo -*- @settitle Libavfilter Documentation@titlepage@center @titlefont{Libavfilter Documentation}@end titlepage @top @contents @chapter Introduction Libavfilter is the filtering API of Libav. It is the substitute of thenow deprecated 'vhooks' and started as a Google Summer of Code project. But note that there may still be serious bugs in the code and its APIand ABI should not be considered stable yet! @chapter Tutorial In libavfilter, it is possible for filters to have multiple inputs andmultiple outputs.To illustrate the sorts of things that are possible, we canuse a complex filter graph. For example, the following one: @exampleinput --> split --> fifo -----------------------> overlay --> output            |                                        ^            |                                        |            +------> fifo --> crop --> vflip --------+@end example splits the stream in two streams, sends one stream through the crop filterand the vflip filter before merging it back with the other stream byoverlaying it on top. You can use the following command to achieve this: @example./avconv -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 mirroredonto the bottom half. Video filters are loaded using the @var{-vf} option passed toavconv or to avplay. Filters in the same linear chain are separated bycommas. In our example, @var{split, fifo, overlay} are in one linearchain, and @var{fifo, crop, vflip} are in another. The points wherethe linear chains join are labeled by names enclosed in squarebrackets. In our example, that is @var{[T1]} and @var{[T2]}. The magiclabels @var{[in]} and @var{[out]} are the points where video is inputand output. Some filters take in input a list of parameters: they are specifiedafter the filter name and an equal sign, and are separated each otherby a semicolon. There exist so-called @var{source filters} that do not have a videoinput, and we expect in the future some @var{sink filters} that willnot have video output. @chapter graph2dot The @file{graph2dot} program included in the Libav @file{tools}directory can be used to parse a filter graph description and issue acorresponding textual representation in the dot language. Invoke the command:@examplegraph2dot -h@end example to see how to use @file{graph2dot}. You can then pass the dot description to the @file{dot} program (fromthe graphviz suite of programs) and obtain a graphical representationof the filter graph. For example the sequence of commands:@exampleecho @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 graphdescribed by the @var{GRAPH_DESCRIPTION} string. @include filters.texi @bye