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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 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 vflip

Flip the input video vertically.

@example

./ffmpeg -i in.avi -vfilters "vflip" out.avi

@end example

@bye