Jerky playback Dharma B2 and SVN /Ion

If you turn on sync playback to display, you can see a sync and an error value when you press 'o' during playback, you want that sync value to remain stable.

However if you get a constantly drifting a/v sync without sync playback to display, then there's either a problem with the file you're playing or the soundcard is running at a slightly different speed than the system clock.

bobo1on1 Wrote:If you turn on sync playback to display, you can see a sync and an error value when you press 'o' during playback, you want that sync value to remain stable.

However if you get a constantly drifting a/v sync without sync playback to display, then there's either a problem with the file you're playing or the soundcard is running at a slightly different speed than the system clock.

ok...so

1. with "sync to display" the "a/v" and "sync" drift represent a difference between vsync rate and audio clock.
2. without "sync to display" the "a/v" drift represents a difference between system clock and audio clock.

The "sync" value is a percentage of a frame time I assume. The error value I have no idea about.

The audio clock adjust method to compensate for any discrepancy in either case should give the least quality reduction in audio. Can you please confirm that this should work with passthrough - at least within some limited range of discrepancy between the appropriate clocks.

It seems for now that I need to set "sync to display" and keep adjusting the refreshrate until I find the one that keeps the same "sync" value for as long as possible. Currently I have this at a drift of 1% per 5mins (for 23.976).

EDIT: but note that I have trouble with the vblanks "missed" value increasing forever at (3-10per sec), especially when pressing the movie info button

Don't worry about the missed vblanks, it automatically compensates for them.
It does indicate that your system could be under high cpu/gpu load.

bobo1on1 Wrote:Don't worry about the missed vblanks, it automatically compensates for them.
It does indicate that your system could be under high cpu/gpu load.

Well it is certainly not under high CPU load, and the GPU figures look low too. The card can handle much much higher frame rates and bitrates than I am using at present that it for sure. Perhaps something to do with the return path to overlay the info, and the PCI x1 lane being used?

That's possible.

I may buy a card for further testing in a different machine to isolate the cause of this.

Thanks for your help.

Could you please reply on the issue of passthrough though. I want to be sure whe using passthrough which modes of compensation are possible (As your comment prior has me worried that none will work).

You can use audio clock or drop/dupe, but if the refreshrate differs too much from the video fps, you get jerks with audio clock and audio distortion with drop/dupe.

jerks in audio or video?

Video.

Assuming I can get a close match then issue becomes what does xbmc choose as its video/audio offset each time a movie is played. It seems every time I play I get a different starting sync value - which I assume implies a different offset between the two. This would mean up to 40ms swing in audio sync that would have to be adjusted manually each time movie is played. Am I wrong?