I use xv output in KDE. With other output drivers, the colors are wrong, gone, no video at all, or the CPU usage is high.
When I pause a video, and execute "xset dpms force off" in a terminal, the screen turns off, but after a few seconds (~5 to 8) it turns on again.
P.D. I don't use screensaver, I just want the screen to turn off after a specific amount of time (but not on video play), the one specified in the OS settings.