I'm running Arch64 on my home desktop with KDE4.2. Since the upgrade from 4.1 the performance of displaying any video content (DVB, avi files etc.) with either mplayer/smplayer or kaffeine (xine-backend) went down the drain. However, I'm not entirely sure if things went wrong due to the update or just around the same time.
I can't really tell what it is, it just feels slow, it starts to stutter (and seems to repeat a couple of frames) every time you click somewhere else on the desktop or do something else like moving a window or opening KRunner. This is anoying because I used to put kaffeine on the second monitor to watch some TV (DVB) while working but I can't do that anymore. The sound plays ok, only displaying the video frames seems to be messed up.
Maybe related to that, I can't use any of kaffeine's deinterlacing algorithms anymore. I have the feeling they look worse than before (more like 256 colors) and they drop the video framerate even further.
I used to have a Nvidia Quadro NVS (which exhibited the problem) but replaced it with a GeForce 9500GT which at first seemed to reduce (but not solve) the problem. However, I have the feeling now that things stayed pretty much the same.
Recently, I played around with glxgears and had to realize that the problem exists there as well. As long as nothing else is happening on the desktop, the window gets updated correctly (although smooth is something else... it's more like the video stuff I described above). But as soon as I click somewhere, open a menu or something glxgears starts to stutter just like video does.
I have TwinView enabled but also tried things without it - no change.
I dropped my old xorg.conf in favor of a new (clean) one - no change.
I tried different video outputs (xv, gl, gl2) - no change.
I enabled/disabled desktop effects - no change.
I tried different driver versions (currently using the 180.29-3 from pacman, but also tried 180.22, .27 and .35 in the past) - no change.
Tried the latest beta (185.13) - no change.
Tried the nopat option - no change either.
The funny thing is that everything else works fine... desktop effects are smooth, even the video performance does not drop (further) when moving the video window itself with transparency and all that stuff.
I'm running out of ideas... really.