M2v and AC3 audio resync

[monteie]

Is there a way that I can easily resync the audio between my M2v video file and my AC3 audio. During the encoding process the sync has been lost. Can someone suggest a tool I can use here?

Thanks

[pijetro]

I haven't had the challenge, but if i did, i would.....

Use VirtualDubMpeg, and save out the .AC3 as a .WAV, and remerge with the video file, and by using the audio skew correction, save the corrected .WAV back out....

Recompress the .WAV, and Mux the two streams once again...

Good luck!!!

[monteie]

Use VirtualDubMpeg, and save out the .AC3 as a .WAV, and remerge with the video file,

Can you tell me how to remerge the two together again?

and by using the audio skew correction, save the corrected .WAV back out....

Where is the skew correction?

Recompress the .WAV, and Mux the two streams once again...

How do I recompress the .wav? How do I mux the two streams together.

I am quite new to this tool.

[pijetro]

Before we chase our tails, lets get something out of the way...

Is the audio out of synch from the beginning, or gradual stretching??
This warrants two different methods...
The common mistake most people make, is using audio with a 44100hz sample rate as the source file...
Since DVD spec requires 48000hz, synch can sometimes become an issue, since people don't do the extra step of Sample Conversion..

[dafreak]

Before we chase our tails, lets get something out of the way...

Is the audio out of synch from the beginning, or gradual stretching??
This warrants two different methods...
The common mistake most people make, is using audio with a 44100hz sample rate as the source file...
Since DVD spec requires 48000hz, synch can sometimes become an issue, since people don't do the extra step of Sample Conversion..

yep, this is one of the most common mistakes of audio/video synch.

another is if you converted the video using different framerates.

[monteie]

Through more investigation it is off when playing in Dr. Divx player. So the source is the issue. How do I fix it?

[pijetro]

How do I fix it?

By first answering my question..Is it synch, or stretch??

[monteie]

K.... Here we go. The Divx plays with sync problems in Dr. Divx Player 2.5.5 but as soon as I touch one of the fast forward or reverse buttons the audio syncs. Wiht WMP 9 the audio is sync'd. With PowerDVD v.5 it plays sync'd. When I encode and author it using TMPGEnc and TMPGEnc DVD Author the final DVD has audio sync issues. (this procedure)
I am so frustrated with this. I have a new 3GHZ machine that just crushes data and I can't get my first project to work. Had less issues with the 1GHZ laptop.

If anyone can help me with this you would so be my hero!

[monteie]

Looking at the DVD I created it sems that the audio sync is off by the same amount throughout the DVD.

[LisaB]

Well, pijetro, I don't know about VDubMpeg...but I can tell you that VDubMod creates a flawed AC3 stream when you try to add a positive delay. It is not able to create true AC3 frames of silence.

Now, VDubMod does okay *if* the delay is negative, and *if* the delay is an integral multiple of 32ms.....because in this case it just chops off an integral number of AC3 frames at the start.

VDubMod is too stupid to cut AC3 on frame borders, and that is the root of the problem. Do you know that VDubMpeg does better? Have you actually analyzed the output AC3 stream after a cut?

You can check your ac3 with a tool like BeSplit or delaycut.

[monteie]

Have you actually analyzed the output AC3 stream after a cut?

You can check your ac3 with a tool like BeSplit or delaycut

I really don't know how to do this. I should have mentioned this before but I am not really familiar with a lot of this software because for the most part I just do what the guides tell me. Some of the simpler software isn't an issue but something lik VirtualDub I don't consider simple (yet).

[pijetro]

Okay LisaB, you're scaring me
To avoid any issues with .AC3, and delay, i simply uncompress to a .WAV, and use the .WAV file for further usage..Once everything is okayed with the .WAV (ie synch or editing), then i recompress to .AC3...

Monteie wrote:

The Divx plays with sync problems in Dr. Divx Player 2.5.5 but as soon as I touch one of the fast forward or reverse buttons the audio syncs.

I suspect that the version of Dr. Divx, and/or the way it's using your codecs could be an issue, especially since the other players play okay..
You've probably got a good .AVI, but if not Vdub has a function for checking bad frames. So does VirtualDubMp3Freeze (something like that). Do this first..


So this is what i'd do...
Open up VirtualDub, and open up your .AVI.
Go to Video>Direct Stream Copy
Audio>Full Processing Mode
Audio>Compression (choose PCM uncompressed at the top)
Audio>Conversion (48000 stereo, 16bit)
File>Save .Wav..
Exit Vdub..
Reopen up VirtualDub, and open up your .AVI.
Go to Audio>No Audio.
Video>Direct Stream Copy
File Save as .AVI..

This will save an .AVI without audio..
Exit Vdub..
Reopen up VirtualDub, and open up your silent .AVI.
Video>direct stream copy
Go to Audio>direct stream copy
Audio>Wav Audio.
Select the afformentioned .WAV file..

Check for synch on the timeline..if it's off, then go to Audio>Interleaving, and fix the values. As you add or subtract milliseconds, you can immediately see the effects on your video..
Once you've reached the desired synch, then go to Save .AVI..

Reopen up VirtualDub, and open up your newly synched .AVI.

You should have a good .AVI to work with..
Use this for DVD encoding..

This should be a guide :P

[monteie]

Buddy you are the Man! I so salute you . Thank you so much. I have been slaving over this piece of f@$% crap project for a while now!

Thanks again....


Ps - Your the man... One more salute

[LisaB]

Wel, pijetro, you should be scared...because guess what, the little audio glitches caused by bad AC3 frames are rarely noticeable when playing on the computer, but they *are* when playing on a standalone DVD player that has divx playback capability (like the philips 642)...

Remember that a single AC3 frame is only 32 ms, so one or two edits won't cause a noticeable desynch (but still a glitch) on a standalone divx player. Software media players are much more forgiving, and constantly resynching.

But don't go around re-encoding everything...you don't need to...just learn to use tools like BeSplice, delaycut, ac3fix, and AC3 delay corrector......do your editing as usual, but at the end of the day, run your ac3 through one of the tools mentioned above!

[pijetro]

but they *are* when playing on a standalone DVD player that has divx playback capability (like the philips 642)..

Except for simple .WAV to .AC3 encoding, i never really knew much about the inner workings of the .AC3 format..
I used to convert DivX movies onto DVD (which required some basic understandings of Vdub), but since i've learned about the wonderfull world of ripping, shrinking, backing up to a 50 cent disk, i shy away from DivX, let a lone standalones that support it..
It's frustrating watching somebody elses crappy encodes...

[monteie]

Well at the end of the day Pijetro offered a solution to the issue which is exactly what I was looking for. LisaB if you have a better solution an suggested process I'm all ears.