Originally Posted by MadCatX
It's a bit of a long shot, but for me it helps if set PowerMizer to maximum performance instead of adaptive. Unless I do that, Full HD videos are considerably sluggish and my card (9800 GTS) doesn't ever go past performance level 2.
I just did some extra testing and the issue I'm having doesn't appear to be directly linked to the card not switching to a higher power level. If I launch a Full HD video in mplayer (custom built revision 37174), the entire system enters a sluggish and unresponsive mode, even the mouse cursor lags. When that happens, I have to set the PowerMizer to max performance, system gets immediately back on it's feet and I can set the PowerMizer to adaptive again. The card then returns to power level 2 and remains there, the playback is smooth and everything else works as expected. I don't remember seeing this issue before upgrading to 285.05.09, but I don't play Fulll HD vids much though. It also doesn't matter whether the compositing is switched on or off in KWin.