Yet another out of synch problem - sorry! :(

[pbush77]

I searched and searched, but could find nothing to help me with this. If there are other posts which address it, please send me to them!

My problem is this. I have VOB files on my hard drive which play perfectly. However, when I demux and remux them into mpeg2 files, the audio is out of synch! I thought it was just a delay issue, so used ac3 delay to try and sort that out, but then I found that the delay moves from beginning to end (sound is behind at first, then the video gradually gets behind). Obviously this is an audio length not matching the video length issue, but I cannot figure out what is the real problem!

I am using VOBedit to demux the files, and I checked with Virtualdub and Goldwave and found that the ac3 and m2v files are indeed different. As I said, the files play perfectly as VOB's, so I thought there was a set delay that was being lost upon the demux, but this cannot be the case with different file lengths, can it? Is this the fault of VOBedit? If so, what else could I use to demux the files more accurately? If it isn't VOBedit causing the problem, what is the problem?

Does anybody know how I can sort this out? I have many of these files and it's driving me crazy!

[bottle-necked]

sound is behind at first, then the video gradually gets behind

That sounds like a gradual sync issue. An offset problem is simple to repair since it remains the same throughout the video. Here it changes as the video plays.

Have you tried playing the original vob files in VirtualDubMPEG2 or VirtualDubMod? If they contain AC3 audio you will need AC3 ACM Decompressor installed.

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[pbush77]

No, I haven't tried the VOB files in any of those, only the m2v files to check the length. I don't understand, though - what am I looking for when opening the VOB files in Virtualdubmod, etc.? Or what will I then do in that program?

Thanks for your help, by the way.

[bottle-necked]

Open the vob file in either of those programs and play them at different points in the video testing audio sync. Either of these programs will play the file as it is...... If it's actually out of sync it will show up in there.

Simple offset can be corrected by adjusting Audio Interleaving "Delay Audio By" and putting in your delay number. This would be the difference in lenght (time) of the audio and video streams. It's a little hard to get the exact amount in some cases since VD only shows the exact audio length under certain audio compressions. This can be worked around but will require a few additional steps. I don't remember if VD will show the time with AC3 but I think it will.

Gradual sync can be repaired but will require additional steps. I can't remember the guide I found on this but I will look and post the link if I find it.

[bottle-necked]

How to fix gradual loss of sync once and for all (GUIDE)

https://www.videohelp.com/forum/userguides/140540.php

[pbush77]

Okay, that would be very helpful, as I cannot find a guide that makes sense anywhere! I'm pretty sure it's a gradual out-of-synch problem, because I tried playing it in two other players (than media player) before coming to that conclusion. However, I'll try the VD method to make absolutely sure. It's such a nightmare, I can't believe it!

[bottle-necked]

I don't remember if VD will show the time with AC3 but I think it will.

Nope... Doesn't show it. I was wrong....

[dafreak]

just a quick question here. Is there any particular reason why you have to demux the audio and video and then multiplex them again?

seems kind of silly to me to demux audio and video for no apparent reason.

[pbush77]

Yes - the sound was only encoded on one channel, so I convert the ac3 to wav, mix it into stereo sound, and then convert back into ac3 for the remuxing.