Statistics
| Branch: | Revision:

ffmpeg / doc / libavfilter.texi @ e0b33d47

History | View | Annotate | Download (3.38 KB)

1
\input texinfo @c -*- texinfo -*-
2

    
3
@settitle Libavfilter Documentation
4
@titlepage
5
@center @titlefont{Libavfilter Documentation}
6
@end titlepage
7

    
8
@top
9

    
10
@contents
11

    
12
@chapter Introduction
13

    
14
Libavfilter is the filtering API of Libav. It is the substitute of the
15
now deprecated 'vhooks' and started as a Google Summer of Code project.
16

    
17
Integrating libavfilter into the main Libav repository is a work in
18
progress. If you wish to try the unfinished development code of
19
libavfilter then check it out from the libavfilter repository into
20
some directory of your choice by:
21

    
22
@example
23
   svn checkout svn://svn.libav.org/soc/libavfilter
24
@end example
25

    
26
And then read the README file in the top directory to learn how to
27
integrate it into ffmpeg and ffplay.
28

    
29
But note that there may still be serious bugs in the code and its API
30
and ABI should not be considered stable yet!
31

    
32
@chapter Tutorial
33

    
34
In libavfilter, it is possible for filters to have multiple inputs and
35
multiple outputs.
36
To illustrate the sorts of things that are possible, we can
37
use a complex filter graph. For example, the following one:
38

    
39
@example
40
input --> split --> fifo -----------------------> overlay --> output
41
            |                                        ^
42
            |                                        |
43
            +------> fifo --> crop --> vflip --------+
44
@end example
45

    
46
splits the stream in two streams, sends one stream through the crop filter
47
and the vflip filter before merging it back with the other stream by
48
overlaying it on top. You can use the following command to achieve this:
49

    
50
@example
51
./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]
52
@end example
53

    
54
where input_video.avi has a vertical resolution of 480 pixels. The
55
result will be that in output the top half of the video is mirrored
56
onto the bottom half.
57

    
58
Video filters are loaded using the @var{-vf} option passed to
59
ffmpeg or to ffplay. Filters in the same linear chain are separated by
60
commas. In our example, @var{split, fifo, overlay} are in one linear
61
chain, and @var{fifo, crop, vflip} are in another. The points where
62
the linear chains join are labeled by names enclosed in square
63
brackets. In our example, that is @var{[T1]} and @var{[T2]}. The magic
64
labels @var{[in]} and @var{[out]} are the points where video is input
65
and output.
66

    
67
Some filters take in input a list of parameters: they are specified
68
after the filter name and an equal sign, and are separated each other
69
by a semicolon.
70

    
71
There exist so-called @var{source filters} that do not have a video
72
input, and we expect in the future some @var{sink filters} that will
73
not have video output.
74

    
75
@chapter graph2dot
76

    
77
The @file{graph2dot} program included in the Libav @file{tools}
78
directory can be used to parse a filter graph description and issue a
79
corresponding textual representation in the dot language.
80

    
81
Invoke the command:
82
@example
83
graph2dot -h
84
@end example
85

    
86
to see how to use @file{graph2dot}.
87

    
88
You can then pass the dot description to the @file{dot} program (from
89
the graphviz suite of programs) and obtain a graphical representation
90
of the filter graph.
91

    
92
For example the sequence of commands:
93
@example
94
echo @var{GRAPH_DESCRIPTION} | \
95
tools/graph2dot -o graph.tmp && \
96
dot -Tpng graph.tmp -o graph.png && \
97
display graph.png
98
@end example
99

    
100
can be used to create and display an image representing the graph
101
described by the @var{GRAPH_DESCRIPTION} string.
102

    
103
@include filters.texi
104

    
105
@bye