mirror of https://git.ffmpeg.org/ffmpeg.git
114 lines
3.8 KiB
Plaintext
114 lines
3.8 KiB
Plaintext
\input texinfo @c -*- texinfo -*-
|
|
|
|
@settitle Video Hook Documentation
|
|
@titlepage
|
|
@sp 7
|
|
@center @titlefont{Video Hook Documentation}
|
|
@sp 3
|
|
@end titlepage
|
|
|
|
|
|
@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 module implements a text overlay for a video image. Currently it
|
|
supports a fixed overlay or reading the text from a file. The string
|
|
is passed through strftime so that it is easy to imprint the date and
|
|
time onto the image.
|
|
|
|
You may also overlay an image (even semi-transparent) like TV stations do.
|
|
You may move either the text or the image around your video to create
|
|
scrolling credits, for example.
|
|
|
|
Text fonts are being looked for in a FONTPATH environment variable.
|
|
|
|
Options:
|
|
@multitable @columnfractions .2 .8
|
|
@item @option{-c <color>} @tab The color of the text
|
|
@item @option{-F <fontname>} @tab The font face and size
|
|
@item @option{-t <text>} @tab The text
|
|
@item @option{-f <filename>} @tab The filename to read text from
|
|
@item @option{-x <expresion>} @tab X coordinate of text or image
|
|
@item @option{-y <expresion>} @tab Y coordinate of text or image
|
|
@item @option{-i <filename>} @tab The filename to read a image from
|
|
@end multitable
|
|
|
|
Expresions are functions of these variables:
|
|
@multitable @columnfractions .2 .8
|
|
@item @var{N} @tab frame number (starting at zero)
|
|
@item @var{H} @tab frame height
|
|
@item @var{W} @tab frame width
|
|
@item @var{h} @tab image height
|
|
@item @var{w} @tab image width
|
|
@item @var{X} @tab previous x coordinate of text or image
|
|
@item @var{Y} @tab previous y coordinate of text or image
|
|
@end multitable
|
|
|
|
You may also use the constants @var{PI}, @var{E}, and the math functions available at the
|
|
FFmpeg formula evaluator at (@url{ffmpeg-doc.html#SEC13}), except @var{bits2qp(bits)}
|
|
and @var{qp2bits(qp)}.
|
|
|
|
Usage examples:
|
|
|
|
@example
|
|
# Remember to set the path to your fonts
|
|
FONTPATH="/cygdrive/c/WINDOWS/Fonts/"
|
|
FONTPATH="$FONTPATH:/usr/share/imlib2/data/fonts/"
|
|
FONTPATH="$FONTPATH:/usr/X11R6/lib/X11/fonts/TTF/"
|
|
export FONTPATH
|
|
|
|
# Bulb dancing in a Lissajous pattern
|
|
ffmpeg -i input.avi -vhook \
|
|
'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' \
|
|
-acodec copy -sameq output.avi
|
|
|
|
# Text scrolling
|
|
ffmpeg -i input.avi -vhook \
|
|
'vhook/imlib2.dll -c red -F Vera.ttf/20 -x 150+0.5*N -y 70+0.25*N -t Hello' \
|
|
-acodec copy -sameq output.avi
|
|
@end example
|
|
|
|
@section ppm.c
|
|
|
|
It's basically a launch point for a PPM pipe, so you can use any
|
|
executable (or script) which consumes a PPM on stdin and produces a PPM
|
|
on stdout (and flushes each frame).
|
|
|
|
Usage example:
|
|
|
|
@example
|
|
ffmpeg -i input -vhook "/path/to/ppm.so some-ppm-filter args" output
|
|
@end example
|
|
|
|
@bye
|