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@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 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.

@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 ``width'' and ``height'' 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 ``width'' and ``height'' is 0.

@section format

Convert the input video to one of the specified pixel formats.
Libavfilter will try to pick one that is supported for the input to
the next filter.

The filter accepts a list of pixel format names, separated by ``:'',
for example ``yuv420p:monow:rgb24''.

The following command:

@example
./ffmpeg -i in.avi -vfilters "format=yuv420p" out.avi
@end example

will convert the input video to the format ``yuv420p''.

@section noformat

Force libavfilter not to use any of the specified pixel formats for the
input to the next filter.

The filter accepts a list of pixel format names, separated by ``:'',
for example ``yuv420p:monow:rgb24''.

The following command:

@example
./ffmpeg -i in.avi -vfilters "noformat=yuv420p, vflip" out.avi
@end example

will make libavfilter use a format different from ``yuv420p'' for the
input to the vflip filter.

@section null

Pass the source unchanged to the output.

@section scale

Scale the input video to width:height and/or convert the image format.

For example the command:

@example
./ffmpeg -i in.avi -vfilters "scale=200:100" out.avi
@end example

will scale the input video to a size of 200x100.

If the input image format is different from the format requested by
the next filter, the scale filter will convert the input to the
requested format.

If the value for ``width'' or ``height'' is 0, the respective input
size is used for the output.

If the value for ``width'' or ``height'' is -1, the scale filter will
use, for the respective output size, a value that maintains the aspect
ratio of the input image.

The default value of ``width'' and ``height'' is 0.

@section slicify

Pass the images of input video on to next video filter as multiple
slices.

@example
./ffmpeg -i in.avi -vfilters "slicify=32" out.avi
@end example

The filter accepts the slice height as parameter. If the parameter is
not specified it will use the default value of 16.

Adding this in the beginning of filter chains should make filtering
faster due to better use of the memory cache.

@section vflip

Flip the input video vertically.

@example
./ffmpeg -i in.avi -vfilters "vflip" out.avi
@end example

@chapter Available video sources

Below is a description of the currently available video sources.

@section nullsrc

Null video source, never return images. It is mainly useful as a
template and to be employed in analysis / debugging tools.

It accepts as optional parameter a string of the form
``width:height'', where ``width'' and ``height'' specify the size of
the configured source.

The default values of ``width'' and ``height'' are respectively 352
and 288 (corresponding to the CIF size format).

@chapter Available video sinks

Below is a description of the currently available video sinks.

@section nullsink

Null video sink, do absolutely nothing with the input video. It is
mainly useful as a template and to be employed in analysis / debugging
tools.

@bye
