Thread: mplayer vdpau
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Old 09-30-09, 03:46 PM   #1210
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Default Re: mplayer vdpau

Originally Posted by Stephen Warren View Post
Skipping display of a frame requires skipping sync-to-vblank for that queue entry. There are implementation difficulties doing this; it's probably not possible.
So no philosophical reasons, just implementation difficulties doing otherwise.
And again I re-iterate: The application should be aware of what it's doing and what the presentation queue's capabilities are. The application is the only software in possession of complete knowledge required to choose the correct frames to skip.
At least the algorithm I currently intend to use in MPlayer will only use the same timing information as is available to VDPAU - MPlayer will drop a frame if the next frame can be shown during the same VSYNC.
Attempting to display 50fps content on a 24Hz display doesn't make sense without frame-dropping. The presentation queue does not implement frame dropping. Hence, the application must.
Well IMO your original claim about how the presentation queue would work without extra information if used correctly becomes quite meaningless if you define "correct" use to require getting extra information about the display frame rate and using that to drop frames before placing them in the queue...
I suppose that in a TwinView configuration, it's not currently possible for an application to know which display device VDPAU is syncing to for the blit-based presentation queue (the overlay-based presentation queue syncs to both display devices independently). We'll think about the best solution for this.
So I suppose the overall result is that for implementation reasons VDPAU won't support cases where multiple queue timestamps fall within the same VSYNC, and applications need to get display device refresh rate information and handle framedropping if they want to avoid the frames being delayed in that case. The best way to get the refresh rate information will be defined later.
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