[MPlayer-dev-eng] NVidia AV frame sync

[Attila Kinali]

On Thu, Aug 12, 2004 at 08:53:19AM +0100, Ed Wildgoose wrote:
> Sorry, assumed that the topic was better understood.

Never assume that something as complicated as video playback
on something as obfuscated as the PC architacture with is understood
at all :)

> Mplayer is actually already very smooth for me, and I assume that this 
> is down to a relaxed fashion in tracking frame timing (letting it vary a 
> little within some tolerance)? 

Yes, there is a small tolerance, mostly because we are dealing
with hardware that is not perfect. Ie gives inexact numbers.
So MPlayer tries to smooth this out a little bit. How much this is
can be controlled by various options.

> I think some of the reasons for the 
> slight jitter from time to time are down to audio card that I am using 
> which doesn't report exact free space, only whether it has consumed a 
> whole buffer or not.  So the exact audio sync can not be maintained from 
> the card results alone, only the time since we last fed the card data 
> for example,

How about using -autosync then ? Quoting the manpage:
"Try -autosync 30  to smooth  out problems with sound drivers which do
not implement a perfect audio delay measurement."

> So the nvidia device can't be used for clocking the audio for sure, but 
> only for assisting with frame dropping calculations to get the frame 
> cadence as smooth as possible.  Actually I have taken the time to get a 
> video mode with 50hz timing and it's already very smooth for me - 
> perhaps this extra tweak is not worth the effort..?

I dont see exactly how a video card should help with timing
problems. The only reason why i's use the vsync info is to switch
buffers, but that should be already done by the xv driver from
x11/nvidia.

If you want an additianal timing source, the system clock or the rtc
should be used as it doesnt depend on a graphic card with the shittiest
driver the world has ever seen.
But then, this is already done, see the manpage.

			Attila Kinali