I'm recording streaming movies from an IE window. The recording starts out OK. But as time goes on the video lags behind the audio. By the end of 30 minutes its off by several seconds. Video is otherwise smooth but the sync problem is disconcerting

Please advise.

I'm running Vista64 on a 2.1GHz T8100 dual core 4GB Ram system.
RVC settings ar 6000 videobitrate, 25 fps, 256kbps sound.

John