| \input texinfo @c -*- texinfo -*- |
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| @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 |
| @command{ffmpeg} or to @command{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 |