93 lines
3.0 KiB
Plaintext
93 lines
3.0 KiB
Plaintext
\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
|
|
@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
|