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@settitle Video Hook Documentation 
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@sp 7 
@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