Re: Automatic VDPAU V-sync in TwinView
If you use the overlay-based presentation queue, it will sync-to-vblank on both displays at once.
When using the blit-based presentation queue, it will always sync to a single statically configured display, as set by that environment variable.
The most likely way to get the blit-based presentation queue is to disable the X composite extension. See the VDPAU section of the README for complete details on the selection algorithm.