libavfilter.texi 2.92 KB
Newer Older
1 2
\input texinfo @c -*- texinfo -*-

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

8 9 10
@top

@contents
11 12 13

@chapter Introduction

14
Libavfilter is the filtering API of Libav. It is the substitute of the
15 16 17 18 19
now deprecated 'vhooks' and started as a Google Summer of Code project.

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

20 21
@chapter Tutorial

22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38
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
39
./avconv -i input -vf "[in] split [T1], fifo, [T2] overlay=0:H/2 [out]; [T1] fifo, crop=iw:ih/2:0:ih/2, vflip [T2]" output
40 41
@end example

42
The result will be that in output the top half of the video is mirrored
43 44
onto the bottom half.

45
Video filters are loaded using the @var{-vf} option passed to
46
avconv or to avplay. Filters in the same linear chain are separated by
47 48 49 50 51 52 53 54 55 56 57 58 59 60 61
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.

62 63
@chapter graph2dot

64
The @file{graph2dot} program included in the Libav @file{tools}
65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89
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.

90
@include filters.texi
Stefano Sabatini's avatar
Stefano Sabatini committed
91

92
@bye