Re: Mplayer - vdpau - composite disabled screen flashing
Here are a couple more things to try:
1) When the flashing is happening, can you run nvidia-settings, and look at the PowerMizer page. Is your GPU running at the highest performance level?
2) When the flashing is happening, does running glxinfo once a second, or running glxgears (make sure you have OpenGL sync-to-VBLANK on in nvidia-settings) make any difference?