[mythtv] Question on Xv output and NuppelVideoPlayer

Isaac Richards ijr at po.cwru.edu
Thu Jul 1 15:00:22 EDT 2004

On Thursday 01 July 2004 01:57 am, Clyde Stubbs wrote:
> I have some questions about the video output in NuppelVideoPlayer,
> in particular about the Xv implementation.
> I've not used any of the other video output methods other than Xv,
> but I have looked through the code for the various other drivers.
> I'll explain my understanding of how it works - I'd appreciate
> confirmation or correction if I've got something wrong.

XvPutImage just starts the process of transferring the image to the video 
card.  It takes a non-zero amount of time for that to happen, which varies 
from machine to machine.  Because of this, we need to call XvPutImage _well 
before_ the desired display time, thus the PrepareFrame call happens after 
the last frame was displayed, but before the current frame should be 
displayed.  The XSync call makes it wait and not return until the image has 
been displayed (ie, the XvPutImage request has been completed).  Separating 
the two allows the a/v sync code to be a bit more accurate.

Try removing the XSync call from Show() and see what happens.


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