Audio/Video synch problem on HD MPEG-4 channals

[genpix]

Real-time play of HD MPEG-4 (Cyberlink H.264 + nVideo Audio) is very smooth.
CPU core is loaded upto 80% (second core is at about 1% level) on my Athlon x2 3800+.
So, there is still some headroom (20% or so).
Nevertheless, Audio/Video is not in synch.
Anybody has/had similar problem? Any obveous setting to check?

PS: MPEG-2 is always fine (nVidia Pure Video + nVideo Audio)

[genpix]

hmm...,
looks like not enough CPU power
Cause recorded file has a perfect synch.
Just a real time playback of 1080i has synch problem (720p is OK, though).