AC3 - How do I stretch it

[Nello_AU]

I have an xVid file with ac3 soundtrack that goes out of sync for approx 9 minutes. It is 15 frames behind at first then slowly gets back into sync in about 9 minutes.

I have isolated the AVI/ac3 section where the audio sync is out and extracted both video and audio streams.

I extracted ac3, 15 frames from the beginning to get the audio in sync at the beginning.

I converted to WAVE in BeSweet and used Goldwave to stretch the audio back to the length of the Video section.

Audio is back in sync after using nandub to mux the 2 together and play.

My problem is, how do I do the audio stretch with the AC3 file.

If I convert from wave back to AC3 I lose the 5.1 channels.

I tried using change frame rate in BeSweet but the frame change is very small and it would not accept it (25000 to 24998).

Does anyone know how I can correct the sync problem in the AC3 file without losing the 5.1 channels

[BJ_M]

convert to 6 wav files first in besweet and then stretch those 6 wave files one at a time in goldwave , then encode back to 5:1

[tygrus2000]

When you converted it to wave with Besweet, that just made a 2 channel wave file and lost the 5.1 info.

You have to decode it to 6 channel mono waves using something like Softencode, then do your little bit of editing on each file, then put them back together into an AC3 again using Softencode.

I would actually try demuxing video and ac3, then re-encoding it back together rather than do all that little sound editing. That should work, it does with most file that have audio drift or syncing issues.

Tygrus

[Nello_AU]

Thank you very much for the prompt replies.

I have never tried Softencode so I will check it out.

I have already converted the AC3 to 6 waves using Besweet and adjusted the time of each wave file in Goldwave.

Trouble with this approach is I cannot get besweet to re-encode them back to AC3.

I have added the stretched wave files to an .LST file but I get a GPF of besweet 1.4 every time. I have never had any problems with Besweet until trying to re-encode to ac3.

I have search DSPGuru's site for info on an .lst file.

I have just places the files in Notepad as follows:
c:\Wave1-C.wav
c:\Wave1-LFE.wav
c:\Wave1-SR.wav
etc ...
and saved as a .lst file. If this correct

Again many thanks for your replies.

Nello

[Nello_AU]

OK I have now updated to latest BeSweet and have output 6 wave files.

I have also found the correct syntax for the .lst format so no more crashes.

But I have the following problems using BeSweet:
- The 6 wave files all contain the same sound. How do I stop this.

- I have stretched the time of the 6 waves to the correct time but when I
re-encode them back to ac3 the sound is high pitched (fast).

I cannot download softEncode as it is no longer available.

Any help on the above would be greatly appreciated.

I would actually try demuxing video and ac3, then re-encoding it back together rather than do all that little sound editing. That should work, it does with most file that have audio drift or syncing issues

Not sure how to do this with ac3.

I am happy to try other solutions if someone could point out a relevant guide to use.

Thanks

[tygrus2000]

DVD2AVI can demux ac3 files and TMPG DVD author can put them backtogether as you encode.

If you think you are getting 6 channels with the same sound, then your source was probably never 5.1 but listen carefully to each track, there may just be minor differences in each audio track.