Another audi sync problem

[Stavros]

I have recently been trying to covert an AVI file to an MPEG2 file. I saved the audio from the file as a WAV file and converted from 44100Hz to 48000Hz using Virtual Dub.

Because the audio file was shorter that the video file I stretched it using Goldwave.

I then proceeded to encode the original video AVI as video and my new audio file as audio. When I viewed my new MPEG I found that the audio was completely out of sync.

I fed this new file into Goldwaveand found that the audio had only very slightly shrank from 00:49:47:040 to 00:49:47:024.

Aswell as being surprised that this slight change could make such a big difference the strangest thing is that the audio is behind the video. This does not seem right if the audio is shorter.

Can anyone please advise why this might happen and possibly tell me hoe to fix it.

[wee haggis]

If the AVI is XVID...do not extract the audio.
Just encode as is.

[mats.hogberg]

It could be that the original AVI is interlaced with a skew; if you separate the A from V, you lose this, and when you put them back toghether, they will be out of sync.
Original AVI:

A:  ----------
V:------------

Separated and then multiplexed:

A:----------
V:------------

So, either multiplex with skew, or insert some silence (at beginning of A)to compensate.

/Mats

[Stavros]

The file is DIVX

Mats.hogberg Inserting a delay at the beginning would not work as the audio de-sync is far worse at the end of the viseo than at the beginning.

I was not sure what you meant by 'multiplex with skew' because if I am not meant to de-multiplex the AVI then I do not have two files to mux.

I took what you said as encode the file as it is. I did that and there is a huge improvement. I then added an audio delay at the beginnig of the MPEG and saw even further improvements. Thanks for the advice.

Unfortunately the video still isn't perfect. The reason I tried de-multiplexed the file in the first place was because I'd had audio sync problems in the past with related files. What I did to fix them was to stetch the audio. Since I can't de-multiplex this file to stretch the audio, is there any other way to compensate.

Mats.hogberg If I did not follow your instruction correctly, please let me know.

Thanks again.

[mats.hogberg]

It wasn't clear from you original post that the sync went gradually worse thru the movie, hence my suggestion to align A/V by adding some silence at the start (if the audio is ahead of the video - my mistake! I see now that audio is behind video - this would call for cutting a bit at the start of audio).
My point is that the audio and video streams in an AVI doesn't have to be "aligned" with eachother. When you take them apart, you have no idea where they ought to start in realtion to eachother.
On the other hand, if the sunc changes thru the movie, this is usually due to selecting another frame rate as output than the input video, or that the audio routines has problems with the audio stream somewhere in the conversion. I recently did a AVI to SVCD where it starts fine, drifts slightly to be almost annoying in the middle, then gets better again to be perfect in the end. To even think about trying to fix this makes me sweat!

/Mats