[MPlayer-users] stripes in image with (x)mga and ffmpeg on G200

Brent Roman brent at mbari.org
Mon Jan 28 20:11:01 CET 2002


> One more question, what is RAM access contention supposed to mean in
> this context?  I would be most delighted if somebody could educate me
> on the matter.

This occurs because the RAM on the video card is accessed by both
the video hardware (to drive the Video DAC) and the low-level software
drivers.  There must be some mechanism to insure that at both do not
try to access the RAM at the same instant.  When you run the 
card at high resolution, refresh rate or color depth, it increases
the memory bandwitch necessary to drive the Video DAC.  This leaves
less time left over for software to update the Video RAM and, thus,
makes RAM contention more likely.

If it is RAM contention, you will find that just lowering the 
vertical refresh rate from say 85hz to 60hz will improve the
situation.  If you are already at 60hz, then you probably have
to start thinking about another video card or try to find out
if there's something that can be done to the software to have it
time its accesses to avoid RAM contention.  Any such
hypothetical software fix is likely to hurt proformance, so if
you're already "on the edge" to CPU utilization, don't even bother.

Hope this helps.

- brent

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