Why would using VOBs give different results to using M2V?

[FlimsyFeet]

Just noticed something strange - it's not a big problem, but I'm curious to know if it's me that doing something wrong:

Method 1. I use DVD Decrypter to copy the VOBs off a DVD, then select these VOBs as my input for DGIndex.

Method 2. I use DVD Decrypter to demux the video stream, then select the demuxed M2V file as the input for DGIndex.

(Video is 23.976 progressive, and I use forced film field operation both times)
Case 1 seems to have a few additional frames onto the start of the video. I think Case 2 is correct because this video is in sync with the demuxed audio.

What could cause this to happen?

[Guest]

I don't know how DVDDecrypter demuxes, so I can't comment on the differences seen at the start of the stream.

But if you are getting a sync problem with the VOB, then try hitting > followed by [ to move in by one GOP before doing Save Project. We are seeing some VOBs with silly stuff at the start that results in a bad sync value.

If that doesn't help, then please make the first part of the VOB available for analysis.

[FlimsyFeet]

OK, some more details. The video on the original DVD is actually PAL 25fps, sorry I got myself confused over this (I was attempting at an NTSC conversion). I used ignore pulldown, not forced film.

Used DVD Decrypter to demux the M2V and AC3. There is 0ms delay on the AC3. If I reauthor these video and audio files they are in sync. If I convert the AC3 to WAV, use mpeg2sourc (d2v file form the M2V) wavsource and audiodub then the script plays in sync in MPC.

I also decrypted the VOB files in file mode. If I then make a d2v project from the vobs, then the video lags by 12 frames, and it's no longer in sync with my wavsource. I didn't try demuxing the audio with DGIndex to see what delay value that reported, I assumed it would be the same. Also if I move one GOP in, does it cut the start of the AC3 for me?

Anyway, I don't think this strangeness is specific to DGIndex. I tried opening th M2V in VirtualDubMod, then tried opeing the first VOB file directly. Same thing happened, there were 12 frames extra at the beginning of the video.

So maybe it's something to do with the way I've decrpted the VOBs?

Do you still want to see a sample of the start of the VOB? (I tried cutting the first 30seconds with ChopperXP, but it prodeced a much longer file. I must have entered the times wrong.)

[Jeffster]

So maybe it's something to do with the way I've decrpted the VOBs?
Yes, use IFO mode not File mode.
There's probably a blank cell before the movie (possibly unreferenced) which is throwing off the sync. They're typically around 0.5 sec long (12 frames) and contain no audio.

[Guest]

Yes, rip in IFO mode and then just do what I told you to do, i.e., start the project in by a GOP or two. Yes, it will cut the AC3 audio as well. Then be sure to adjust by the reported delay value.

I didn't try demuxing the audio with DGIndex to see what delay value that reported, I assumed it would be the same. You can't make assumptions like that, because we don't know the details of DVD Decrypter's demuxing algorithm.

Finally, although it's harmless here because you have PAL, don't get in the habit of using Ignore Pulldown Flags, because it can destroy audio sync in some cases. Use Honor Pulldown Flags instead, as explained in the User Manual.