Nearly all PC hardware has a single video (YUV) overlay engine. Which means it not possible to display more that one overlay video rectangle at a time. Most hardware also has non-overlay mechanisms for scaling and displaying YUV data, and many drivers expose these as Xv adaptors. For example, the driver I'm using exposes 1 overlay adaptor and 32 blit adaptors on my NVIDIA card. If the apps are smart enough to look for free adaptors, the first instance will use the overlay adaptor and subsequent ones will use the blit adaptors.
Thanx very much for this info! I did not know that. This gives me a great opportunity to pester app developers to improve Xv usage.
Is the number of blit adaptos hardware limited or is it determined by the xfree86 module?
Furthermore is my understanding correct: a single window app will be able to use the hardware accelerated YUV video scaling engine. Others will have to use software (or is it hardware but non-overlay mechanism?) scaling/transfromation of YUV data that still can be visualized using Xv? What is the performance hit of using video overlay to non-overlay mechanism?
And if someone wonders how my questions started: Sun Microsystems recently announced sth called Looking Glass (http://www.sun.com/bigadmin/xtreme/shows/lg_media.html) (WARNING - Quick Time movie!)
I was wondering whether they were using video overlays for the movie apps and whether it would be possible to use many apps per a single overlay hardware.
Best regards:
al_shopov
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