reference must be 3 because both "fields" are used as reference, and buffer_hints must include readable since we might memcpy from the old frame. Originally committed as revision 20923 to svn://svn.ffmpeg.org/ffmpeg/trunk
Patch by Michael Tison (gmail address: blackspike@....) Originally committed as revision 20890 to svn://svn.ffmpeg.org/ffmpeg/trunk