Posted by blackburst@aol.com on 09/08/05 13:35

William Davis wrote:
> 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.

In the case of my work set-up (a small TV studio) and my home setup, I
have gone out-of-the-box: No setting of data rates on either camera or
DVD recorder. Straight firewire or comps cables.

The firewire run is very sensitive to any breaks in the "control
track". A slight blip (usually made when a volunteer switches to the
play mode on the camera to check their footage) will cause the audio to
unlock during the dub process.

One unrelated side note re: Katrina:
I've been working on a great historical documentary with a buddy who is
a producer at the PBS affiliate in New Orleans. He was missing for
several days, but I finally got him on his cel. He asked me to look at
satellite photos online to see if his house and station were still
there. I had the sad duty to tell him that both were there, but
underwater. And all the BetaCam master tapes of our project are gone,
as well as all his other work. I presume the station's FCP and Avid
suites are unsalvagable. This tragedy affected a lot of things. I count
my own blessings.

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