Audio and video different length

[dkelly701]

I have a mpg file that started out as a vob. I used VOB2MPG to create the mpg. When I open the file in VirtualDobMod and click on Streams and then Report, it shows the video and audio to be of different lengths.



The original VOB plays correctly and is in sync. I am trying to demux the audio and video, reencode only the video to make it smaller, and then put them back together in my authoring software.

Any ideas appreciated.

[manono]

Hi-

There may be no problem. Maybe one of the stream lengths is being reported incorrectly. Maybe the audio ends a second before the video, and will be in synch all the way through. That's pretty common. If you're not so lucky, you'll just have to set a delay equal to the amount of the difference between the 2 lengths. You may be able to do that in the authoring app. If not, you can remove the delay with AC3 Delay Corrector or some such. If you still have the original IFOs and the Vobs, you can open the IFO in PGCDemux and check to see if there's a delay.

You probably should have used PGCDemux or VobEdit in the first place. Looks to me like you're doing an extra step.

[dkelly701]

I started out demuxing with PGcDemux and that was when I first discovered my sync issue. It starts out in sync but at the end it appears to be about 1 second off.

I have a DVD with a 5.1 soundtrack. I am trying to encode with TMPGEnc Express 3.0. to reduce the size but keep the 5.1 audio. I have the AC3 plugin but it is only 2 channel. What I did was to deumux, reencode the video only using TMPGEnc 3.0 and then added the 5.1 soundtrack back in when I authored with TMPGEnc DVD Author 1.6. This appeared to be successful except the audio got out of sync as it got closer to the end.

I thought that it might be better if I demuxed with TMPGEnc (that's why I used VOB2PMG on the second attempt) but I got the same result.

I understand the hardest sync problem to correct is the one that gets gradually worse.

By the way, I did check for audio delay and it was 0. Am I going about this the hard way?

[manono]

Hi-

That makes it much harder to diagnose. You gave much more useful info in your second post. First off, the act of demuxing alone won't change the audio or video length. To get the exact lengths, I open the audio in HeadAC3he and check, and make a D2V Project File in DGIndex for the video, and an AviSynth Script File and then open that in VDubMod. I don't believe it will give the exact video length if you just open the MPG or M2V in VDubMod. Could be wrong there, I guess, but I know that a D2V in an .avs is exact. But maybe you're not using AviSynth for this job.

You could test that it's OK after the Demux by Remuxing it right afterwards with something simple and good, like Muxman, and check to see if it's out of synch. It'll take awhile, since the video is so long, but it would reassure you that it's not already out of synch after the demux.

So, assuming the audio is untouched and the length unchanged, then your problem is most likely at the encoding stage or the quthoring stage. Unfortunately, since I don't use either of those TMPGEnc products, I can't help you there.

But progressive asynch is hell to fix. It can be done, but you shouldn't have to. This is NTSC? And you ran Pulldown after the encode, or maybe using TMPGEnc during the encode? The reason I ask is that running Pulldown incorrectly can make it out of synch. It has to be the encoding, the pulldown (if there is any) or the authoring that's doing it. I've never encountered this problem, don't use TMPG products, and can't help. However, since they are real popular around here, I'm sure that someone else here can help. You might detail all the encoding settings and steps, to help pin it down further. Sorry, not much help, I'm afraid.

[manono]

By the way, you aren't doing a PAL to NTSC conversion, or changing the framerate in any way, are you?

[dkelly701]

No, no conversion or framerate change. I will try some of your suggestions and see what I can figure out. Thanks for you help.