Video - Audio synchronization (again)

[dcassidy]

Hi,
I have a troublesome file which I am trying to 'perfect'. The audio stream starts off in sync but by the end of the 40 odd minutes it is about 1.5 second AHEAD of the video. I noticed that the Video stream size is 42:12.24 and the Audio is 42:10.080 - THIS may be significant ?

1. I Unpack the AVI if necessary using the MPEG4Modifier
2. I extract an AC3 file from the AVI using the ffmpegGUI as I always do.
3. I load up VirtualDubMod and set the Video to Direct Stream Copy.
4. I disable the MP3 stream and add the AC3 stream.

Now, no end of messing/playing with/adjusting the Interleaving setting comes up with a solution. e.g. Delay Audio track by, Offset audio to maintain a/v sync, Preload x ms of audio etc.

So, what am I missing...

Any help appreciated...

Cheers,

Desmond.

[NormaJ]

I would say that your audio source is mp3 vbr at 44.100Hz. As Ffmpeggui is resampling to 48.000 by default, this could cause desynch. Don't resample if no need. And, if needed, better extract wav with VirtualDub/Mod, and in this same moment set to resample (under Conversion). Later conversion to AC3 should not give synch issues.
HTH

[dcassidy]

But this is the way I do ALL my files ?? WHy this one ???

[NormaJ]

From my experience, most avi are already 48.000 Hz. audio. If you don't use a tool such Gspot, you wont even notice. But I open in Gspot each and every thing I'm working with, and I've realized and, by the way, suffered, that when VBR and 44 to 48 are involved together, things go wrong.
I also could be wrong, of course.