[mythtv] Playback optimization..

[Isaac Richards]

I just committed a patch by (mostly) Matt Zimmerman that really improves the 
speed of video playback when using mpeg4.  rtjpeg is also improved a little, 
but not nearly as much..  Basically, it removes extra full-framesize copies 
from the playback pipeline.  So, this drops the CPU used in live-tv mode down 
under 70% on my XP 1800+ with mpeg4 @ 3300 bps, 640x480, and it bottoms out 
below 60% at times, depending on the scene.  The rtjpeg codec is helped as 
well, but not quite to the same degree.

Anyway, I think I've gotten all the bugs worked out of this, so if people can 
please confirm that things still work for them, that'd be great.  If there's 
any cases of video corruption, or crashes, or whatnot, please let me know.

Isaac