Originally Posted by poltsy
Or unchecking the option to disable desktop effects for fullscreen windows. Turning on effects while vdpau is being used seems to have an extremely high chance of triggering this bug.
I confirm, having UnredirectFullscreen=false in kwinrc fixes the issue.
I didn't know this option. I found out what does it mean here :
Another workaround is to use mplayer2 which doesn't suffer from this bug.