[pvrusb2] Audio/video sync (was re: Jumpy Video in Mythtv)

[Rod Smith]

On Saturday 30 June 2007 12:58, Mike Isely wrote:
> On Thu, 28 Jun 2007, Mark Goldberg wrote:
>
> > It also seems that there still may be a slight audio delay or video
> > delay, not enough to obviously tell, but enough so you can tell
> > something is not quite right. Is there any adjustment for this in the
> > encoding side. I know you can adjust it during playback, but it would
> > be nice to have it recorded ideally.
>
> There isn't any adjustment in the driver.  The video and audio are
> combined into mpeg within the device itself not in the driver (that
> after all is the entire point of this device), and I don't recall seeing
> any adjustments provided by the cx23416's API.

FWIW, I've noticed audio/video sync problems, too, although they're not 
severe. The problem is most noticeable for me on WGBH, which is the PBS 
station delivered by my cable provider. I suspect that WGBH's sync is a 
little off and the PVR-USB2 is also a little bit off. I usually get good sync 
by adjusting about 60-100ms in MythTV's playback, although the amount I need 
to adjust seems to vary from one recording to the next. (I don't know if that 
variability is from variability on the WGBH/Cox Cable or PVR-USB2 side.) I 
suspect that about half of the 60-100ms is from the PVR-USB2 and the other 
half from WGBH/Cox.

I only mention this because the problem is much less noticeable when I record 
using my AverMedia AverTV M150, which is an internal card based on the 
CX88 "Blackbird" chipset. I suspect that the PVR-USB2's chipset is just a bit 
off in this respect (probably about 30ms, which is barely noticeable if the 
original signal's sync is good). If there's no way for you to adjust this 
given the chip interfaces, then that's just the way it is.

-- 
Rod Smith, rodsmith at rodsbooks.com
http://www.rodsbooks.com
Author of books on Linux, FreeBSD, and networking