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123 lines
4.3 KiB
Plaintext
123 lines
4.3 KiB
Plaintext
\input texinfo @c -*- texinfo -*-
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@settitle Video Hook Documentation
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@titlepage
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@sp 7
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@center @titlefont{Video Hook Documentation}
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@sp 3
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@end titlepage
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@chapter Introduction
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The video hook functionality is designed (mostly) for live video. It allows
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the video to be modified or examined between the decoder and the encoder.
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Any number of hook modules can be placed inline, and they are run in the
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order that they were specified on the ffmpeg command line.
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A few modules are provided and are described below. They are all intended to
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be used as a base for your own modules.
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Modules are loaded using the -vhook option to ffmpeg. The value of this parameter
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is a space separated list of arguments. The first is the module name, and the rest
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are passed as arguments to the Configure function of the module.
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The modules are dynamic libraries: They have different suffixes (.so, .dll, .dylib)
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depending on your platform. And your platform dictates if they need to be
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somewhere in your PATH, or in your LD_LIBRARY_PATH. Otherwise you will need to
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specify the full path of the vhook file that you are using.
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@section null.c
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This does nothing. Actually it converts the input image to RGB24 and then converts
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it back again. This is meant as a sample that you can use to test your setup.
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@section fish.c
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This implements a 'fish detector'. Essentially it converts the image into HSV
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space and tests whether more than a certain percentage of the pixels fall into
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a specific HSV cuboid. If so, then the image is saved into a file for processing
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by other bits of code.
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Why use HSV? It turns out that HSV cuboids represent a more compact range of
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colors than would an RGB cuboid.
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@section imlib2.c
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This module implements a text overlay for a video image. Currently it
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supports a fixed overlay or reading the text from a file. The string
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is passed through strftime so that it is easy to imprint the date and
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time onto the image.
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This module depends on the external library imlib2, available on
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Sourceforge, among other places, if it is not already installed on
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your system.
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You may also overlay an image (even semi-transparent) like TV stations do.
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You may move either the text or the image around your video to create
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scrolling credits, for example.
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Text fonts are being looked for in a FONTPATH environment variable.
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Options:
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@multitable @columnfractions .2 .8
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@item @option{-c <color>} @tab The color of the text
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@item @option{-F <fontname>} @tab The font face and size
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@item @option{-t <text>} @tab The text
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@item @option{-f <filename>} @tab The filename to read text from
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@item @option{-x <expresion>} @tab X coordinate of text or image
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@item @option{-y <expresion>} @tab Y coordinate of text or image
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@item @option{-i <filename>} @tab The filename to read a image from
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@end multitable
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Expresions are functions of these variables:
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@multitable @columnfractions .2 .8
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@item @var{N} @tab frame number (starting at zero)
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@item @var{H} @tab frame height
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@item @var{W} @tab frame width
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@item @var{h} @tab image height
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@item @var{w} @tab image width
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@item @var{X} @tab previous x coordinate of text or image
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@item @var{Y} @tab previous y coordinate of text or image
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@end multitable
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You may also use the constants @var{PI}, @var{E}, and the math functions available at the
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FFmpeg formula evaluator at (@url{ffmpeg-doc.html#SEC13}), except @var{bits2qp(bits)}
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and @var{qp2bits(qp)}.
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Usage examples:
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@example
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# Remember to set the path to your fonts
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FONTPATH="/cygdrive/c/WINDOWS/Fonts/"
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FONTPATH="$FONTPATH:/usr/share/imlib2/data/fonts/"
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FONTPATH="$FONTPATH:/usr/X11R6/lib/X11/fonts/TTF/"
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export FONTPATH
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# Bulb dancing in a Lissajous pattern
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ffmpeg -i input.avi -vhook \
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'vhook/imlib2.dll -x W*(0.5+0.25*sin(N/47*PI))-w/2 -y H*(0.5+0.50*cos(N/97*PI))-h/2 -i /usr/share/imlib2/data/images/bulb.png' \
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-acodec copy -sameq output.avi
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# Text scrolling
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ffmpeg -i input.avi -vhook \
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'vhook/imlib2.dll -c red -F Vera.ttf/20 -x 150+0.5*N -y 70+0.25*N -t Hello' \
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-acodec copy -sameq output.avi
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@end example
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@section ppm.c
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It's basically a launch point for a PPM pipe, so you can use any
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executable (or script) which consumes a PPM on stdin and produces a PPM
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on stdout (and flushes each frame).
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Usage example:
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@example
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ffmpeg -i input -vhook "/path/to/ppm.so some-ppm-filter args" output
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@end example
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@bye
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