Audio Synch Problem - AC3, XViD, 2 Clip DVD

[voy1d]

I'm currently trying to encode face off to xvid using Gordian Knot.

I've encoded both sides of the two sided dvd and wish to join them, however when trying to join them the audio goes out of synch at the halfway point.

I've tried playing with the frame delay (if this is the correct term) in VirtualDub Mod to rectify this however still cannot get the audio to synch the video.

I've also tried following the recommendations from the following posts:
http://forum.doom9.org/showthread.php?s=&threadid=17237
http://forum.doom9.org/showthread.php?s=&threadid=50276
http://forum.doom9.org/showthread.php?s=&threadid=54655
http://forum.doom9.org/showthread.php?s=&threadid=56366

and the following guides:
http://ifoedit.wh.fr0zen.com/joinclip.html

However I still am unable to get the audio to synch in the second half. Both halfs of the movie are encoded at the same bitrate and using AC3.

I apologise if this is the wrong forum to post such a query but I'm now completely stumped.

Thanks

[ammck55]

Welcome:

You've done a good deal of homework, more than most first time posters, and I compliment you on your effort. I don't have the solution you seek, but I will offer some advice. Re-read the forum rules from the top of the page, the Stickies, and edit the title of your thread. A poor title will hamper your efforts to get help, but you can fix this quite easily. I would imagine you'll get some help soon. Good luck!

ammck55

[manono]

Hi-

Take the second half of the movie and adjust the delay by the amount it's asynch after joining them. That will leave the second half asynch, but after joining them it'll be OK.

Another thing you can do is to reencode the audio of the first part in BeSweet. It has a checkbox to "Append Silence Of xxx ms". Then just add a silence equal to the amount of the asynch of the second part. That way the second half is in synch whether by itself or joined to the first half.

Movies which are spread over 2 DVDs sometimes have the audio of the first half shorter than the video length. When you join the second half, the audio "slides up" against the first half's audio, and throws the second half off. At least I think that's what happens. I can't think of any other way to explain it. I haven't encoded Face-Off, but that's the case with Gangs Of New York, and I've read it's also the case with LOTR Extended.

A better solution is to encode the first half of the movie using AviSynth's Trim Command cutting off the black frames at the end of the first half equal to the length of the audio asynch. The best way, perhaps, is to join the vob files so you encode the whole movie at once and, again, cut out the extra black frames.

But all of these solutions depend on you figuring out the exact amount of the delay (or of the missing audio at the end of part 1). One way is to open the first half .avi or .avs in VDubMod and write down the exact length. Then open the first half audio in HeadAC3he and write down the exact length. Then subtract one from the other. Lots of ways to skin a cat.

[voy1d]

Well, I'd like to thank you, because the problem has been resolved.

As suggested I opened the file in Nandub & looked at the exact length of video, opened the ac3 file in HeadAC3he & wrote down the exact length, video - audio = delay.

I then set a delay offset for the audio at the end of the first half to fill the gap and then joined the two in Nandub and it works perfectly.

and if anyone wants to know the delay is 816 milliseconds...

Cheers

[Codesmith]

I have two AVI files with AC3 audio in perfect sync, but the second half is out of sync when I join them.

My understanding is that this is caused by the audio and video lengths in the first half not matching.

1) Is there a easy way to determine the audio length from the avi, or will I have to extract the AC3 file first?

2) Assuming that the audio track is shorter than the video, is it better to trim the video or extend the audio?

3) Whats the best programs to do any of the above?

No need to give detailed instructions, I am sure that once I know what to do I can figure the rest out on my own.

[killingspree]

1) just load the avi in virtualdub(mod), open stream list and write down exact length of the audio - easy as that!

2) personal preference... i'd trim the video because this way it would spare me from having to demux and remux again!

3) virtualdubmod

[ToiletDuck]

@killingspree. I am trying to do the samething and so far have found your post to be the most relevant. However there is a problem for me. The audio time of the first .avi is 1:34:17.600 while the actual frame time go to .817 or something like that and I can't get it to stop at .600. Could you possibly elabarte a little more with a few steps I can follow to do this? Thanks a bunch.
Duck

[Codesmith]

The first avi ended in a spot where trimming would have been noticed.

So instead I opened the 2nd part, added a 213 ms delax and saved (using Direct Stream Copy).

Then I opened the 1st part, appened the 2nd and saved.

I there anyway to do this in one step, or this the easiest way to do this?

[killingspree]

Originally posted by Codesmith

I there anyway to do this in one step, or this the easiest way to do this?

no actually iirc this is as easy as it gets!

@Toilet Duck: Well you can either do it the way Codesmith did it, or just cut a little more. you're not able to cut at .600 because there isn't a keyframe at this exact point. since you can only cut on keyframes (or else the video up to the next keyframe will be corrupted) just cut at the last keyframe in the first part and then append the second one. the audio will be cut with the video automatically, so you'll be sure to have exact same audio and video lengths!

anyway, come to think of it - you should probably do it as Codesmith has done it. less work and less noticable too...

cheers
steVe

[stephanV]

Originally posted by killingspree
no actually iirc this is as easy as it gets!

@Toilet Duck: Well you can either do it the way Codesmith did it, or just cut a little more. you're not able to cut at .600 because there isn't a keyframe at this exact point. since you can only cut on keyframes (or else the video up to the next keyframe will be corrupted) just cut at the last keyframe in the first part and then append the second one. the audio will be cut with the video automatically, so you'll be sure to have exact same audio and video lengths!

not exactly true... your selection must start at a keyframe (if you dont, VDub will do it for you ;) ), wether it ends on a keyframe or not doesnt really matter.


anyway, come to think of it - you should probably do it as Codesmith has done it. less work and less noticable too...



yep :)