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\input texinfo @c -*- texinfo -*-
@settitle Libavfilter Documentation
@titlepage
@sp 7
@center @titlefont{Libavfilter Documentation}
@sp 3
@end titlepage
@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.ffmpeg.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 -vfilters "[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{-vfilters} 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 Available video filters
When you configure your FFmpeg build, you can disable any of the
existing video filters.
The configure output will show the video filters included in your
build.
Below is a description of the currently available video filters.
@section crop
Crop the input video to x:y:width:height.
@example
./ffmpeg -i in.avi -vfilters "crop=0:0:0:240" out.avi
@end example
``x'' and ``y'' specify the position of the top-left corner of the
output (non-cropped) area.
The default value of ``x'' and ``y'' is 0.
The ``w'' and ``h'' parameters specify the width and height of the
output (non-cropped) area.
A value of 0 is interpreted as the maximum possible size contained in
the area delimited by the top-left corner at position x:y.
For example the parameters:
@example
"crop=100:100:0:0"
@end example
will delimit the rectangle with the top-left corner placed at position
100:100 and the right-bottom corner corresponding to the right-bottom
corner of the input image.
The default value of ``w'' and ``h'' is 0.
@section null
Pass the source unchanged to the output.
@bye
|
