source filter will simply want to re-output the same image multiple times
and reuse a buffer to do it, and the case where the source filter will
output multiple image by modifying a single buffer and outputting it multiple
times.
Commited in SoC by Bobby Bingham on 2007-08-18 02:21:01
Originally committed as revision 12103 to svn://svn.ffmpeg.org/ffmpeg/trunk
b3ab2f7e84