Posted by William Davis on 09/08/05 04:27

In article <1126123690.629187.239950@o13g2000cwo.googlegroups.com>,
"blackburst@aol.com" <blackburst@aol.com> wrote:

> eb7g wrote:
> > Hi there,
> >
> > There used to be the known problem of audio drifting out of sync on long
> > video files. I've been using Sony's DVgate for the last little while,
> > which will split the video into 10 minute segments, so I don't get any
> > drift. But the other day, I digitized 3 miniDV tapes and saved them all
> > as one file per tape.... at about 20 minutes in, the audio started to
> > drift and by the end of each tape the audio was out of sync almost a
> > full second of time.
> >
> > Is this common? How do people without DVgate digitize their audio and
> > keep the sound in sync? If I digitize in Premiere, as one large file,
> > will the sound be out of sync as well?
> >
> > I would have thought this would have been corrected by now. That
> > explains why DVgate splits up the video into chunks.
>
> I note that no other responders have experienced audio drift. I have -
> not in digitizing, but in dubbing from DV tapes to DVD in an OUTBOARD,
> STANDALONE recorder. Happens about 50% of the time, in either composite
> or firewire. Pisses me off. Other pros may not have experienced it, but
> it is a very real problem.

Well, outside of sample rate problems it shouldn't be.

I can see where a composite feed could be prone to timing errors - tho
I'd expect a constant offset, rather than progressive "drift." But in a
Firewire transfer, the video and audio information is locked into a
SINGLE multiplexed datastream.

(NOTE: remember that the AUDIO_TS folder on any common DVD is NOT your
DVD's audio! Unless you're one of the .0001% of the planet who messes
with DVD-AUDIO stuff it's useless. The Video_TS VOB files on any DVD
contain all the video AND audio information of your program - in a
single data structure with both video and audio info locked together. No
practical chance to induce drift that isn't already in the original
encoding.)

So again, if your audio drifts, it's likely because you've gotten
something wrong in data rate or perhaps fed the signal out of sync onto
the disc during encoding - because the DVD spec only has one drummer
and the video and audio MUST march to that drummer, in step.

Good luck solving your problems - but again, I'd START looking at the
data rates you've set for your shooting and/or sequence settings. In my
experience if the video and audio streams are ACTUALLY running at two
subtly different rates, it's a sampling rate problem nearly all of the
time.

FWIW.

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