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342 lines
9.3 KiB
342 lines
9.3 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 -vf "[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{-vf} 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 graph2dot |
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The @file{graph2dot} program included in the FFmpeg @file{tools} |
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directory can be used to parse a filter graph description and issue a |
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corresponding textual representation in the dot language. |
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Invoke the command: |
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@example |
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graph2dot -h |
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@end example |
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to see how to use @file{graph2dot}. |
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You can then pass the dot description to the @file{dot} program (from |
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the graphviz suite of programs) and obtain a graphical representation |
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of the filter graph. |
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For example the sequence of commands: |
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@example |
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echo @var{GRAPH_DESCRIPTION} | \ |
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tools/graph2dot -o graph.tmp && \ |
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dot -Tpng graph.tmp -o graph.png && \ |
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display graph.png |
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@end example |
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can be used to create and display an image representing the graph |
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described by the @var{GRAPH_DESCRIPTION} string. |
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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 @var{x}:@var{y}:@var{width}:@var{height}. |
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@example |
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./ffmpeg -i in.avi -vf "crop=0:0:0:240" out.avi |
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@end example |
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@var{x} and @var{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 @var{x} and @var{y} is 0. |
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The @var{width} and @var{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 @var{width} and @var{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 -vf "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 -vf "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 pad |
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Add paddings to the input image, and places the original input at the |
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given coordinates @var{x}, @var{y}. |
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It accepts the following parameters: |
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@var{width}:@var{height}:@var{x}:@var{y}:@var{color}. |
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Follows the description of the accepted parameters. |
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@table @option |
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@item width, height |
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Specify the size of the output image with the paddings added. If the |
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value for @var{width} or @var{height} is 0, the corresponding input size |
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is used for the output. |
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The default value of @var{width} and @var{height} is 0. |
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@item x, y |
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Specify the offsets where to place the input image in the padded area |
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with respect to the top/left border of the output image. |
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The default value of @var{x} and @var{y} is 0. |
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@item color |
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Specify the color of the padded area, it can be the name of a color |
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(case insensitive match) or a 0xRRGGBB[AA] sequence. |
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The default value of @var{color} is ``black''. |
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@end table |
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@section scale |
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Scale the input video to @var{width}:@var{height} and/or convert the image format. |
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For example the command: |
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@example |
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./ffmpeg -i in.avi -vf "scale=200:100" out.avi |
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@end example |
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will scale the input video to a size of 200x100. |
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If the input image format is different from the format requested by |
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the next filter, the scale filter will convert the input to the |
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requested format. |
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If the value for @var{width} or @var{height} is 0, the respective input |
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size is used for the output. |
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If the value for @var{width} or @var{height} is -1, the scale filter will |
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use, for the respective output size, a value that maintains the aspect |
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ratio of the input image. |
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The default value of @var{width} and @var{height} is 0. |
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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 -vf "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 unsharp |
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Sharpen or blur the input video. It accepts the following parameters: |
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@multitable @columnfractions .2 .5 .1 .1 .1 |
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@headitem Name @tab Description @tab Min @tab Max @tab Default |
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@item @var{luma_msize_x} |
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@tab Luma matrix horizontal size |
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@tab 3 |
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@tab 13 |
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@tab 5 |
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@item @var{luma_msize_y} |
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@tab Luma matrix vertical size |
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@tab 3 |
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@tab 13 |
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@tab 5 |
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@item @var{luma_amount} |
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@tab Luma effect strength |
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@tab -2.0 |
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@tab 5.0 |
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@tab 1.0 |
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@item @var{chroma_msize_x} |
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@tab Chroma matrix horizontal size |
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@tab 3 |
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@tab 13 |
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@tab 0 |
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@item @var{chroma_msize_y} |
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@tab Chroma matrix vertical size |
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@tab 3 |
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@tab 13 |
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@tab 0 |
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@item @var{chroma_amount} |
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@tab Chroma effect strength |
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@tab -2.0 |
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@tab 5.0 |
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@tab 0.0 |
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@end multitable |
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Negative values for the amount will blur the input video, while positive |
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values will sharpen. All parameters are optional and default to the |
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equivalent of the string '5:5:1.0:0:0:0.0'. |
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@example |
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# Strong luma sharpen effect parameters |
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unsharp=7:7:2.5 |
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# Strong blur of both luma and chroma parameters |
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unsharp=7:7:-2:7:7:-2 |
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# Use the default values with @command{ffmpeg} |
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./ffmpeg -i in.avi -vf "unsharp" out.mp4 |
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@end example |
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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 -vf "vflip" out.avi |
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@end example |
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@chapter Available video sources |
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Below is a description of the currently available video sources. |
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@section nullsrc |
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Null video source, never return images. It is mainly useful as a |
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template and to be employed in analysis / debugging tools. |
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It accepts as optional parameter a string of the form |
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@var{width}:@var{height}, where @var{width} and @var{height} specify the size of |
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the configured source. |
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The default values of @var{width} and @var{height} are respectively 352 |
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and 288 (corresponding to the CIF size format). |
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@chapter Available video sinks |
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Below is a description of the currently available video sinks. |
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@section nullsink |
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Null video sink, do absolutely nothing with the input video. It is |
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mainly useful as a template and to be employed in analysis / debugging |
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tools. |
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@bye
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