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175 lines
5.1 KiB
175 lines
5.1 KiB
\input texinfo @c -*- texinfo -*- |
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@settitle Libavfilter Documentation |
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@titlepage |
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@sp 7 |
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@center @titlefont{Libavfilter Documentation} |
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@sp 3 |
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@end titlepage |
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@chapter Introduction |
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Libavfilter is the filtering API of FFmpeg. It is the substitute of the |
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now deprecated 'vhooks' and started as a Google Summer of Code project. |
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Integrating libavfilter into the main FFmpeg repository is a work in |
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progress. If you wish to try the unfinished development code of |
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libavfilter then check it out from the libavfilter repository into |
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some directory of your choice by: |
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@example |
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svn checkout svn://svn.ffmpeg.org/soc/libavfilter |
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@end example |
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And then read the README file in the top directory to learn how to |
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integrate it into ffmpeg and ffplay. |
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But note that there may still be serious bugs in the code and its API |
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and ABI should not be considered stable yet! |
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@chapter Tutorial |
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In libavfilter, it is possible for filters to have multiple inputs and |
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multiple outputs. |
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To illustrate the sorts of things that are possible, we can |
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use a complex filter graph. For example, the following one: |
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@example |
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input --> split --> fifo -----------------------> overlay --> output |
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+------> fifo --> crop --> vflip --------+ |
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@end example |
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splits the stream in two streams, sends one stream through the crop filter |
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and the vflip filter before merging it back with the other stream by |
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overlaying it on top. You can use the following command to achieve this: |
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@example |
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./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] |
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@end example |
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where input_video.avi has a vertical resolution of 480 pixels. The |
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result will be that in output the top half of the video is mirrored |
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onto the bottom half. |
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Video filters are loaded using the @var{-vfilters} option passed to |
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ffmpeg or to ffplay. Filters in the same linear chain are separated by |
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commas. In our example, @var{split, fifo, overlay} are in one linear |
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chain, and @var{fifo, crop, vflip} are in another. The points where |
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the linear chains join are labeled by names enclosed in square |
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brackets. In our example, that is @var{[T1]} and @var{[T2]}. The magic |
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labels @var{[in]} and @var{[out]} are the points where video is input |
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and output. |
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Some filters take in input a list of parameters: they are specified |
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after the filter name and an equal sign, and are separated each other |
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by a semicolon. |
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There exist so-called @var{source filters} that do not have a video |
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input, and we expect in the future some @var{sink filters} that will |
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not have video output. |
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@chapter Available video filters |
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When you configure your FFmpeg build, you can disable any of the |
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existing video filters. |
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The configure output will show the video filters included in your |
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build. |
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Below is a description of the currently available video filters. |
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@section crop |
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Crop the input video to x:y:width:height. |
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@example |
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./ffmpeg -i in.avi -vfilters "crop=0:0:0:240" out.avi |
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@end example |
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``x'' and ``y'' specify the position of the top-left corner of the |
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output (non-cropped) area. |
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The default value of ``x'' and ``y'' is 0. |
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The ``width'' and ``height'' parameters specify the width and height |
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of the output (non-cropped) area. |
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A value of 0 is interpreted as the maximum possible size contained in |
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the area delimited by the top-left corner at position x:y. |
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For example the parameters: |
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@example |
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"crop=100:100:0:0" |
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@end example |
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will delimit the rectangle with the top-left corner placed at position |
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100:100 and the right-bottom corner corresponding to the right-bottom |
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corner of the input image. |
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The default value of ``width'' and ``height'' is 0. |
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@section format |
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Convert the input video to one of the specified pixel formats. |
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Libavfilter will try to pick one that is supported for the input to |
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the next filter. |
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The filter accepts a list of pixel format names, separated by ``:'', |
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for example ``yuv420p:monow:rgb24''. |
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The following command: |
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@example |
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./ffmpeg -i in.avi -vfilters "format=yuv420p" out.avi |
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@end example |
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will convert the input video to the format ``yuv420p''. |
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@section noformat |
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Force libavfilter not to use any of the specified pixel formats for the |
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input to the next filter. |
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The filter accepts a list of pixel format names, separated by ``:'', |
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for example ``yuv420p:monow:rgb24''. |
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The following command: |
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@example |
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./ffmpeg -i in.avi -vfilters "noformat=yuv420p, vflip" out.avi |
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@end example |
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will make libavfilter use a format different from ``yuv420p'' for the |
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input to the vflip filter. |
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@section null |
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Pass the source unchanged to the output. |
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@section slicify |
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Pass the images of input video on to next video filter as multiple |
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slices. |
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@example |
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./ffmpeg -i in.avi -vfilters "slicify=32" out.avi |
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@end example |
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The filter accepts the slice height as parameter. If the parameter is |
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not specified it will use the default value of 16. |
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Adding this in the beginning of filter chains should make filtering |
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faster due to better use of the memory cache. |
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@section vflip |
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Flip the input video vertically. |
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@example |
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./ffmpeg -i in.avi -vfilters "vflip" out.avi |
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@end example |
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@bye
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