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AC3 syncs worse than AIFFs. GOP the issue?

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jay ingles
AC3 syncs worse than AIFFs. GOP the issue?
on Nov 23, 2011 at 4:38:12 am

I've been authoring DVDs with confidence for years and know compressions quite well but just can't wrap my head around this issue.

If transcode a 1 minute clip to M2V (6.2mbps) and AC3, then add it to a track in DVD studio Pro and duplicate it 45 times, how come the sync is out by approx 7-10 frames by the end?

When i do the same but with an AIFF file (from the same master "self contained" video), the output is only 1 frame out.

It seems like a GOP thing but that obviously only relates to the M2V file.

Any insight is appreciated!
Thanks!


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Michael Sacci
Re: AC3 syncs worse than AIFFs. GOP the issue?
on Nov 23, 2011 at 6:21:28 am

has nothing to do with GOP, has to do with you doing something that should never be done. While you can do it, you should never do that. I'm surprised it only out 7-10 frames.


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jay ingles
Re: AC3 syncs worse than AIFFs. GOP the issue?
on Nov 23, 2011 at 12:57:40 pm

I use stories in certain situations, I used (notice, the past tense...no longer will) this method as I suspected it would be less wear on client dvd players as the motor isn't pulling the laser back to the beginning every time the clip is finished.

So what you're suggesting is you should never be putting so many clips into one track. If you've got different content you should either use Stories or render out a timeline in advance of converting to M2V.

Is this the proper way to do it?

Any idea why AC3 falls out of sync and AIFF doesn't?
Thanks for your input michael!


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Bill Stephan
Re: AC3 syncs worse than AIFFs. GOP the issue?
on Dec 7, 2011 at 12:56:49 am

The time duration of 1 frame of Dolby encoded .ac3 audio is slightly different than one video frame. When you duplicate a clip in the authoring app's timeline, you will start to see the cumulative difference in duration when it gets to be 2 frames or more out-of-sync with the picture stream.

I've done this in a spec authoring app (Sonic DVD Creator), and you can trim the streams to keep the sync within one frame. (I've built DVDs of tens or hundreds of commercial spots that way without the need to edit a video master beforehand.) I don't believe you can trim the streams that way in DVDSP.

Bill Stephan
Senior Editor/DVD Author
USA Studios
New York City


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jay ingles
Re: AC3 syncs worse than AIFFs. GOP the issue?
on Dec 7, 2011 at 5:29:56 pm

Interesting. Thanks for the input.

Do you recommend Sonic DVD Creator and a pro option?

I figure i should start looking since DVDSP is no longer supported by apple.


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Bill Stephan
Re: AC3 syncs worse than AIFFs. GOP the issue?
on Dec 10, 2011 at 6:46:15 pm

1. If you know only DVDSP or Adobe Encore and are not trained in spec-level authoring, don't even think about trying Creator (or Scenarist). You will be completely lost FAST. You need to know the rules of the DVD Spec and play by them. The consumer-level apps mentioned above do these things for you.

2. DVD Creator has not been sold or supported for several years. But you can occasionally find used systems for sale. These are OS-9 Mac-based systems that require hardware boards, so you want a system being removed from service in good working order.

3. Pro option? DVD authoring doesn't get any more pro or complex than a spec-level system.

Bill Stephan
Senior Editor/DVD Author
USA Studios
New York City


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