Odd ac3 sync problem

[mayancastle]

Backing up a dvd. It comes on a dvd-9, but I found that if I stripped all the extras, the movie itself would fit on a dvd-5 without any compression. So, I used tmpgenc tools to demux the streams. The m2v, a 2.0 ac3 and a 5.1 ac3.

I then reauthored, but the ac3 files were out of sync. Now, most discussions about ac3 sync issues revolve around a delay problem. But these ac3 streams play about 3 seconds sooner than the video.

I first noticed that the ac3 files were also about 3 seconds shorter than the m2v. So, I thought maybe the audio files shouldn't have started until 3 seconds after the video started. So I nudged the audio files out so that they ended at the same time as the video. That didn't work at all. The audio was way behind.

So, next, I took the ac3 files into Audacity and corrected the length so that both ac3 files were the same length as the m2v file. Audacity only exports as wav, so I then re-encoded to ac3. But they are still out of sync, with the audio still playing before the video. It's now only about 1.5 seconds out of sync instead of 3, but still out of sync.

Does anyone know what the issue might be that the ac3 files just didn't come out in sync to begin with? And what the best way to fix this is?

[freebird73717]

You could have made this a lot easier on yourself. Download vobblanker. Use it to blank the extras. Then you will have a new dvd ready to burn and it will still have your original menus and you won't have any av sync issues.

[manono]

I then reauthored, but the ac3 files were out of sync. Now, most discussions about ac3 sync issues revolve around a delay problem. But these ac3 streams play about 3 seconds sooner than the video.

It's still a delay. There are positive and negative delays. To fix that one you'd apply a 3 second positive delay using DelayCut. But as freebird73717 says, you're just making unnecessary work for yourself. Either do as he says about using VobBlanker to keep the main movie with the menus, or use DVD Shrink to reauthor the movie without the menus. Neither involves demuxing.

Does anyone know what the issue might be that the ac3 files just didn't come out in sync to begin with? And what the best way to fix this is?

Probably an improper decrypt of a newer movie with newer copy protection, one that inserts unreferenced cells. But since you gave no information about the decrypting process, it's hard to be sure.

[Baldrick]

This is not video streaming. Moving you to our dvd to dvd backup forum section.

[mayancastle]

Sorry Baldrick about posting in the wrong forum.

Yes, I'm aware that I could have used Vobblanker or dvdshrink. But, I got somewhat ambitious and decided to edit the menu screens so that there would be no reference to materials that were removed. I tried to do this with vobblanker and pgcedit, but the disc wouldn't play correctly.

The disc was decrypted with DVD Fab 5. Maybe I should have used a more recent version?

[freebird73717]

6.0.1.9 is the most recent version of dvdfab

[AlanHK]

Delaycut, can, as the name suggests, add delays or cut AC3 files without reencoding.

And by the way, Audacity CAN read and write AC3, in version 1.3.7, if you install ffmpeg, but it will reencode in the process.

[AlecWest]

6.0.1.9 is the most recent version of dvdfab

6.0.2.0 as of about an hour ago is now the most recent version. But (grin), I wouldn't count out DVDfab 5 too soon. Read my post here:

https://forum.videohelp.com/topic369036.html#1981066

Regards,
J. Alec West