Re: jerky playback of 1080i under mythtv with vdpau and 9400M (ION)
What does the PowerMizer page say when actually playing back video? There may be a difference between SD and HD video here. On an ION, I'd expect a high level to be automatically selected for video playback (at least with 185.18.14 and later)
The fact it says "battery" rather than "ac" (or whatever the text is) could affect the performance levels PowerMizer chooses.