Or maybe it is a combination of the newest Xserver in Debian experimental and xorg/X11-common 7.4+1, mesa 7.4-2 Intel, and mplayer svn20090412. And my Core2Duo at 2.8 gHz, Intel G33 and KDE 4.2.2 without compositing.
For the first time, I can play a Full HD video (resized to 720p which I guess is more demanding) without any skew, without any skipped image, without any slowdown.
The video is one of the most famous shot with the Canon 5DMkII in Tokyo:
I play it from a console with this command:
mplayer -lavdopts threads=2:fast:skiploopfilter=all "Tokyo-Reality-h264-1080p.mp4"