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Unofficial VirtualDub Support Forums > Newbie Questions > Audio Skew Progressive Over Time.

Posted by: jdg Sep 12 2002, 09:35 PM

I know this question has been asked before by others but I think I've tried the solutions offered and they don't work (or I don't understand them).

When I originally load this file in virtualdub it says it is VBR, so I try nandub:

I have an avi 1h26m56s long. A few minutes in (5), I can use nandub to audio skew it -500 ms, and it is in sync for that area of the avi, but by the end of the film I need an audio skew of -5000 ms (so it is progressively getting worse)

I uncheck the interleaving (I'm not sure what it means exactly), and it doesn't make a difference.

I have saved the audio in a seperate wav file (500 megs, it is exactly 1h26m56s wav file).

How do I get this in sync with the video?

Posted by: Neo Neko Sep 13 2002, 12:52 AM

Have you tried converting the file to a CBR MP3? Undoubtedly your problem comes from the VBR MP3 audio. There is no way to make a proper valid AVI file with VBR MP3 audio. VBR audio in AVI is a no no.

Posted by: jdg Sep 13 2002, 12:58 AM

I assume the wav file is CBR. When I load the original file in virtualdub it states:

---------------------------
VBR audio stream detected
---------------------------
VirtualDub has detected an improper VBR audio encoding in the source AVI file and will rewrite the audio header with standard CBR values during processing for better compatibility. This may introduce up to 17419 ms of skew from the video stream. If this is unacceptable, decompress the *entire* audio stream to an uncompressed WAV file and recompress with a constant bitrate encoder. (bitrate: 77.4 ą 8.7 kbps)
---------------------------

So I did convert to wav. But using audio from the wav with the video from the AVI is desynced in the way I describe above. Converting back to MP3 would yield the same thing I assume. It is 25 FPS, and "change so video and audio durations match" in the video frame rate control also says it would be 25 FPS, so I don't think that would help.

I didn't make the AVI -- I wouldn't use VBR. I'm just trying to resync it.

Posted by: shmooj Sep 23 2002, 03:03 PM

Hey I have the same issue.

AND I am really new to VirtualDub.

So, Neo Neko, how do I convert to CBR MP3? or... how do I "decompress the *entire* audio stream to an uncompressed WAV file" as the program suggests I do too. I cannot find a menu tool for "decompressing"

Posted by: valja Sep 23 2002, 05:14 PM

QUOTE (shmooj @ Sep 23 2002, 06:03 PM)

So, Neo Neko, how do I convert to CBR MP3? or... how do I "decompress the *entire* audio stream to an uncompressed WAV file" as the program suggests I do too. I cannot find a menu tool for "decompressing"

To save audio as uncompressed VAW:

1. Open *.avi file
2. "Audio" -> "Full processing mode"
3. "Audio" -> "Compression" -> "No compression (PCM)"
4. "File" -> "Save VAW..."

Posted by: Neo Neko Sep 23 2002, 08:10 PM

Yes if you save to wav with direct stream copy it puts the VBR MP3 in a WAV file. Same problem. Full processing will convert it to CBR PCM or any other format you choose. But PCM is a good first stop.

Also I noticed that in the new AVISynth there is a command that is supposed to help keep synch on VBR MP3. Don't know how well it works cause I stear clear of VBR MP3 in AVI any more.

Posted by: Glishak Sep 26 2002, 08:42 PM

Im confused, I make VBR mp3 audio tracks for my .avi's all the time and havent experienced any problems. I know its not "legit" but my lame encoded vbr mp3's work perfectly when interleaved with the video Ive used divx 5 to encode.

So if you're interested read on:

use Azid gui and Azid to downmix your DVD's audio to 2/0 instead of 3/2 and then lame encode the .wav file (use razor lame gui if you want), then use nandub to mux the audio and the video. Voila

Posted by: Sarreq Teryx Sep 26 2002, 09:12 PM

same with me, with the lame acm in ABR mode in the real VD even

Posted by: Neo Neko Sep 26 2002, 10:00 PM

It does not matter if it is not "legit" or it "works for you". The fact is it does not work well for 8 out of 10 people. Lets play what if here for a second. What if you some day accidentally happen to get a new PC. Bear with me here I know how unlikely something like that happening is.

And your "new PC" does not keep synch in all your old AVIs. You only have yourself to blame for doing what you did. Now on the other hand if your "new PC" has problems playing AVI with CBR MP3 then you should return it to the store because something in the hardware is defective there.

I used to do VBR MP3 in my AVI as well. But when I learned of the problems with it and saw how hit and miss a solution it is. I stopped doing it all together. I want my files to play perfectly on any system I take them to or that I own. Which means that if I use AVI VBR MP3 is right out.