I’ve had this issue in the past but at one point it seemed to go away. It’s back again so I decided to issue another bug report.
In all driver versions past 343.36 when playing games or watching accelerated video the playback is very choppy. Running glxgears shows:
Running synchronized to the vertical refresh. The framerate should be
approximately the same as the monitor refresh rate.
272 frames in 5.0 seconds = 54.311 FPS
272 frames in 5.0 seconds = 54.384 FPS
271 frames in 5.0 seconds = 54.183 FPS
(this happens regardless of the sync to vblank option)
Drivers 343.36 and lower don’t have this issue (or only very minor). Any driver newer is unusable for video or games. No amount of reinstalling drivers, changing kernel versions or even distros (I tried both Mint and vanilla Ubuntu) helped.
See the timestamps? Your monitor is apparently seen by the driver as hotplugging itself several times a second. No doubt this is what causes your issues. This may well be a driver bug, but it would be good to test with another monitor too.