[mythtv] Newest nvidia driver..

Sam N. Max (snx) snx at rogers.com
Sat Aug 9 03:43:32 EDT 2003

> I didn't verify that the vsync code was actually being
> used.  I am using the 1.0-4363 driver.
> - Eron

One thing I noticed online is that the drivers don't support opengl page
flipping with the TNT/TNT2 cards (which is what I happen to be using).  They
seem to be referring to opengl in the README (and I've seen references that
it doesn't include 640x480, the optimal resolution for NTSC, but does
support 800x600 and 1024x768).  I'm not sure if this is affecting the vsync
code or not.
Definately the ideal situation would be that somewhere along the line,
either automatically by the drivers or by mythtv, page flipping would be
used, though a simple blit-on-vsync from a back buffer would work well too.

I haven't studied the vsync code in great detail, but I doubt it works well
as it looks like there would be a lot of work between the time a vertical
refresh is occuring and the image is being prepared to be put on the screen.
The function "XvShmPutImage" likely involves some color-transformation code,
and even if it doesn't there is an amount of work going on before the
refresh which would need to be minimal so there is enough time for the image
to be copied to the video card's front buffer.  From the look of it Xv
unfortunately isn't so hot when it comes to synching the video the way its
being used, which forces the MythTV code to waste cycles trying to guess the
time when a driver could (should) sync using whatever is necessary for the
specific card.  As I mentioned earlier xawtv does appear to do a better job
of syncing and it is also using Xv, so I'm not sure changing libraries is
necessary but it might be the easiest solution.

- Eron

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