[mythtv] [mythtv-users] HDPVR & 1080i streams

[Stuart Auchterlonie]

On Tue, May 26, 2009 at 07:50:03PM -0400, Mark Buechler wrote:
> 
> I apologize for moving this discussion to mythtv-dev, but nobody on -users
> can help.
> 
> I think this may be ab easy fix, but I'm not seeing it:
> 
> 2009-05-26 19:37:03.786 NVP: Video is 5.90302 frames ahead of audio,
>                         doubling video frame interval to slow down.
> 2009-05-26 19:37:03.852 NVP: Video is 4.88431 frames ahead of audio,
>                         doubling video frame interval to slow down.
> 2009-05-26 19:37:03.919 NVP: Video is 3.85803 frames ahead of audio,
>                         doubling video frame interval to slow down.
> 2009-05-26 19:37:04.840 NVP: Video is 30 frames behind audio (too slow),
> dropping frame to catch up.
> 2009-05-26 19:37:04.844 NVP: Video is 30 frames behind audio (too slow),
> dropping frame to catch up.
> 2009-05-26 19:37:04.848 NVP: Video is 30 frames behind audio (too slow),
> dropping frame to catch up.
> 2009-05-26 19:37:04.852 NVP: Video is 30 frames behind audio (too slow),
> dropping frame to catch up.
> 
> The frontend correctly doubles the frame interval until video is within a
> handful of frames from audio. Then we see a 30 frame jump in the other
> direction almost one second later. From there on, it's a constant ping pong.
> 

This issue is not specific to the HDPVR.

I've seen it occur with normal recordings when running
the cpu close to maxed out. The delay in processing causes
the A/V sync code to "ping-pong" as mark describes.

In control systems theory it's known as overshooting.
Anyone doing control systems theory that fancies
modelling and then tuning the A/V sync "control system"


Stuart