"avcodec decoder debug: concealing 810 DC, 810 AC, 810 MV errors
(h264@0xb782a8b0)"
"main video output warning: late picture skipped (94634)"
The same videos will trigger no errors and would play smoothly in mplayer for example ...
I'm pretty sure this is not a computer performance issue since the videos causing the problems are encoded at low bitrates (around 650-700) and I normally have no problems with h264 HD playback.