[mythtv] Question on Xv output and NuppelVideoPlayer

Isaac Richards ijr at po.cwru.edu
Fri Jul 2 21:42:24 EDT 2004

On Friday 02 July 2004 08:07 pm, Clyde Stubbs wrote:
> On Fri, Jul 02, 2004 at 11:40:49AM -0400, Isaac Richards wrote:
> > event from XvPutImage is sent.  If the driver implementation signals that
> > it's done with the PutImage before it's actually put the image, that's
> > kind of broken, no?
> That's my point. After XSync you are assured that the video card has
> been instructed to display the image, but not that it has actually done
> so.

And due to the way everything else works in Myth, we're pretty much assured 
that it's going to be displayed on the next vblank, which should have happend 
at or around the time the XSync was called if the a/v sync code worked 

> The other, quite orthogonal, point is that the existing videoout_xv code
> assumes that the XSync *initiates* the display of the image, which it
> clearly doesn't. In the OldAVSync case, that's unimportant since
> PrepareFrame and Show are simply called one after the other, but the
> ExAVSync code calls PrepareFrame, then delays, then calls Show. In the
> usual case where the frame rate is half the refresh rate this could result
> in a frame being shown one field early.

That's not the assumption at all.  The existing code assumes that XvPutImage 
initiates the display of the image, and that XSync returns after the image 
has been displayed.


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