\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.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 -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