Patch by Troy James Sobotka - this uses options in newer FFMPEG versions to
convert the full 0-255 YUV range of imported imagery to RGB, rather than
clipping at 16-235.
This functionality is not available yet in an official FFMPEG release
(current precompiled version in /lib for osx at least is v0.5.1 from 2009) so this
won't take effect in that situation, but if you've got a newer ffmpeg on your system
it will work.