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This aims to standardize the English used in the libavfilter documentation, describing the same thing in the same way more often, and significantly reduce the amount of outright errors, including run-on sentences and sentence fragments. Signed-off-by: Luca Barbato <lu_zero@gentoo.org>
93 lines
2.9 KiB
Plaintext
93 lines
2.9 KiB
Plaintext
\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 Libav. It replaces 'vhooks', and
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started as a Google Summer of Code project.
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Note that there may still be serious bugs in the code and its API
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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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| ^
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+------> fifo --> crop --> vflip --------+
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@end example
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splits the stream in two streams, then 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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./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
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@end example
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The result will be that the top half of the video is mirrored
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onto the bottom half of the output video.
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Video filters are loaded using the @var{-vf} option passed to
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avconv or to avplay. Filters in the same linear chain are separated by
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commas. In our example, @var{split}, @var{fifo}, and @var{overlay} are in one
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linear chain, and @var{fifo}, @var{crop}, and @var{vflip} are in another. The
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points where the linear chains join are labeled by names enclosed in square
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brackets. In our example, they join at @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 a list of parameters: they are specified
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after the filter name and an equal sign, and are separated
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by a semicolon.
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There are so-called @var{source filters} that do not take video
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input, and we expect that some @var{sink filters} will
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not have video output, at some point in the future.
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@chapter graph2dot
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The @file{graph2dot} program included in the Libav @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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