Add video crop filter.
[libav.git] / doc / libavfilter.texi
CommitLineData
1f09ab5e
SS
1\input texinfo @c -*- texinfo -*-
2
dba755fa 3@settitle Libavfilter Documentation
1f09ab5e
SS
4@titlepage
5@sp 7
dba755fa 6@center @titlefont{Libavfilter Documentation}
1f09ab5e
SS
7@sp 3
8@end titlepage
9
10
11@chapter Introduction
12
13Libavfilter is the filtering API of FFmpeg. It is the substitute of the
14now deprecated 'vhooks' and started as a Google Summer of Code project.
15
16Integrating libavfilter into the main FFmpeg repository is a work in
17progress. If you wish to try the unfinished development code of
18libavfilter then check it out from the libavfilter repository into
19some directory of your choice by:
20
21@example
22 svn checkout svn://svn.ffmpeg.org/soc/libavfilter
23@end example
24
25And then read the README file in the top directory to learn how to
26integrate it into ffmpeg and ffplay.
27
28But note that there may still be serious bugs in the code and its API
29and ABI should not be considered stable yet!
30
f6112d7f
SS
31@chapter Tutorial
32
1f09ab5e
SS
33In libavfilter, it is possible for filters to have multiple inputs and
34multiple outputs.
35To illustrate the sorts of things that are possible, we can
36use a complex filter graph. For example, the following one:
37
38@example
39input --> split --> fifo -----------------------> overlay --> output
40 | ^
41 | |
42 +------> fifo --> crop --> vflip --------+
43@end example
44
45splits the stream in two streams, sends one stream through the crop filter
46and the vflip filter before merging it back with the other stream by
47overlaying it on top. You can use the following command to achieve this:
48
49@example
50./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]
51@end example
52
53where input_video.avi has a vertical resolution of 480 pixels. The
54result will be that in output the top half of the video is mirrored
55onto the bottom half.
56
57Video filters are loaded using the @var{-vfilters} option passed to
58ffmpeg or to ffplay. Filters in the same linear chain are separated by
59commas. In our example, @var{split, fifo, overlay} are in one linear
60chain, and @var{fifo, crop, vflip} are in another. The points where
61the linear chains join are labeled by names enclosed in square
62brackets. In our example, that is @var{[T1]} and @var{[T2]}. The magic
63labels @var{[in]} and @var{[out]} are the points where video is input
64and output.
65
66Some filters take in input a list of parameters: they are specified
67after the filter name and an equal sign, and are separated each other
68by a semicolon.
69
70There exist so-called @var{source filters} that do not have a video
71input, and we expect in the future some @var{sink filters} that will
72not have video output.
73
74@chapter Available video filters
75
76When you configure your FFmpeg build, you can disable any of the
77existing video filters.
78The configure output will show the video filters included in your
79build.
80
81Below is a description of the currently available video filters.
82
7b018b1d
SS
83@section null
84
85Pass the source unchanged to the output.
86
190c1669
SS
87@section crop
88
89Crop the input video to x:y:width:height.
90
91@example
92./ffmpeg -i in.avi -vfilters "crop=0:0:0:240" out.avi
93@end example
94
95``x'' and ``y'' specify the position of the top-left corner of the
96output (non-cropped) area.
97
98The default value of ``x'' and ``y'' is 0.
99
100The ``w'' and ``h'' parameters specify the width and height of the
101output (non-cropped) area.
102
103A value of 0 is interpreted as the maximum possible size contained in
104the area delimited by the top-left corner at position x:y.
105
106For example the parameters:
107
108@example
109"crop=100:100:0:0"
110@end example
111
112will delimit the rectangle with the top-left corner placed at position
113100:100 and the right-bottom corner corresponding to the right-bottom
114corner of the input image.
115
116The default value of ``w'' and ``h'' is 0.
117
1f09ab5e 118@bye