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@settitle Video Hook Documentation
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@center @titlefont{Video Hook Documentation}
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@chapter Introduction


The video hook functionality is designed (mostly) for live video. It allows
the video to be modified or examined between the decoder and the encoder.

Any number of hook modules can be placed inline, and they are run in the
order that they were specified on the ffmpeg command line.

Three modules are provided and are described below. They are all intended to
be used as a base for your own modules.

Modules are loaded using the -vhook option to ffmpeg. The value of this parameter
is a space separated list of arguments. The first is the module name, and the rest
are passed as arguments to the Configure function of the module.

@section null.c

This does nothing. Actually it converts the input image to RGB24 and then converts
it back again. This is meant as a sample that you can use to test your setup.

@section fish.c

This implements a 'fish detector'. Essentially it converts the image into HSV
space and tests whether more than a certain percentage of the pixels fall into
a specific HSV cuboid. If so, then the image is saved into a file for processing
by other bits of code.

Why use HSV? It turns out that HSV cuboids represent a more compact range of
colors than would an RGB cuboid.

@section imlib2.c

This allows a caption to be placed onto each frame. It supports inserting the
time and date. By using the imlib functions, it would be easy to add your own
graphical logo, add a frame/border, etc.


@bye
