Thanks--I tried doing that with older versions of everything and it worked. However, there appears to be compatibility issues with certain codecs that prevent specifically DivX files from playing fullscreen. Ironically, Xvid encoded files always play full screen, regardless of the flags.
I have the 2003-03-04 version of libffmpeg, the latest I could find. I think whatever recent optimizations that were added brought the decoding process closer to the video buffer but further away from filtering. It runs faster, regardless.
It's a little unusual though. I don't have anything that's in a format other than DivX or Xvid (and my desktop is in the middle of a time-sensitive batch render for Combustion). Thus, I can't really test the phenomena further.
Has anyone else had a similar problem?