Originally Posted by Stephen Warren
For VDPAU, to guarantee tear-free presentation on all monitors at once, you need to make sure that VDPAU is using the overlay-based presentation queue and not the blit-based presentation queue. See the Appendix H (VDPAU) in the README for details on when each is used. When in blit mode, if using TwinView, sync-to-vblank can only work on one monitor at a time. You can set an environment variable to select which. Again, this is describe in more detail in the README.
Hmm, yes, if I both select VDPAU in MPlayer and disable the composite extension in xorg.conf, I find that the tearing goes away.
TwinView would appear to be a red herring, here, since I have only one monitor connected. Is it possible that sync-to-vblank could be syncing to the correct frequency for my monitor but the wrong phase?