@chapter Introduction
+@var{Please be aware that vhook is deprecated, and hence its development is
+frozen (bug fixes are still accepted).
+The substitute will be the result of our 'Video Filter API' Google Summer of Code
+project. You may monitor its progress by subscribing to the ffmpeg-soc mailing
+list at @url{http://lists.mplayerhq.hu/mailman/listinfo/ffmpeg-soc}.}
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.
@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{-x <expression>}@tab x coordinate of text or image
+@item @option{-y <expression>}@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:
+Expressions are functions of these variables:
@multitable @columnfractions .2 .8
@item @var{N} @tab frame number (starting at zero)
@item @var{H} @tab frame height
This example does the same as the one above, but specifies an rgb.txt file
to be used, which has a custom made color in it.
+ # Variable colors
+ ffmpeg -i input.avi -vhook \
+ 'vhook/imlib2.so -t Hello -R abs(255*sin(N/47*PI)) -G abs(255*sin(N/47*PI)) -B abs(255*sin(N/47*PI))' \
+ -sameq output.avi
+
+ In this example, the color for the text goes up and down from black to
+ white.
+
+ # Text fade-out
+ ffmpeg -i input.avi -vhook \
+ 'vhook/imlib2.so -t Hello -A max(0,255-exp(N/47))' \
+ -sameq output.avi
+
+ In this example, the text fades out in about 10 seconds for a 25 fps input
+ video file.
+
# scrolling credits from a graphics file
ffmpeg -sameq -i input.avi \
-vhook 'vhook/imlib2.so -x 0 -y -1.0*N -i credits.png' output.avi