[mythtv-users] drifting audio synch, saa 7134

Alan Calvert cal at graggrag.com
Fri Nov 2 20:49:21 UTC 2007

Sean Goodpasture wrote:
> On 11/2/07, *Alan Calvert* <cal at graggrag.com <mailto:cal at graggrag.com>> 
> wrote:
>     Having put together a modest little SD system for the grandkids, largely
>     from the spare parts pile, there's this one little problem. Audio
>     gradually
>     drifts out of synch, -200ms over ten minutes or so. I might have
>     imagined it,
>     but I swear it drifted back toward centre over a further period.
>     I've searched on a few things, but can't establish if this is a known
>     weakness of v4l in general, or more likely the saa7134 in particular.
>     I'd love to know why it's happening, so any suggestions are welcome.
>     cheers.
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> Not a v4l expert at all, but since this is a framegrabber, could it be 
> that the CPU is overwhelmed with all the processing?  Have you tried 
> tweaking the parameters for capture (changing the encoding types, not 
> encoding the audio, etc.).  I know that on my card that uses the 
> saa7134, I've had some issues with the audio when recording SD (mostly 
> with it dropping completely) and then sometimes the close captioning 
> gets jacked (which is really bad when the audio drops).

Thanks for the info. The cpu is an Athlon X2 4600+ (2.4G), so I think it
should be able to cope. Here, the audio is pretty much rock solid apart from
the gradual synch drift. I'll experiment a bit further with the tweakables,
but this "spare parts" system looks like it'll need a cash injection by way
of new capture cards. Sigh.

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