mirror of https://git.ffmpeg.org/ffmpeg.git
106 lines
3.4 KiB
Plaintext
106 lines
3.4 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.
|
|
|
|
Integrating libavfilter into the main FFmpeg repository is a work in
|
|
progress. If you wish to try the unfinished development code of
|
|
libavfilter then check it out from the libavfilter repository into
|
|
some directory of your choice by:
|
|
|
|
@example
|
|
svn checkout svn://svn.libav.org/soc/libavfilter
|
|
@end example
|
|
|
|
And then read the README file in the top directory to learn how to
|
|
integrate it into ffmpeg and ffplay.
|
|
|
|
But note that there may still be serious bugs in the code and its 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 in.avi -s 240x320 -vf "[in] split [T1], fifo, [T2] overlay= 0:240 [out]; [T1] fifo, crop=0:0:-1:240, vflip [T2]
|
|
@end example
|
|
|
|
where input_video.avi has a vertical resolution of 480 pixels. 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
|
|
ffmpeg or to 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
|