Video and audio sync question

[aussiemac]

I have some SVCDs which I am trying to author using DVD Lab.

I demultiplex the audio as it is 44KHz sampling rate in the SVCD.

I save it as a wav then using AC3Machine convert to 48KHz and into
AC3 format.

I looked at the information when I loaded the SVCD mpg under
VirtualDubMod.

It showed the following:

Video stream
Length : 00: 42: 29: 213

Audio stream or Other stream
Length : 00: 42: 29: 159

There is a difference in the lengths of the two tracks.

This is okay while the SVCD is intact or in its present form.

But what happens when I demux and place the audio and video
into DVDLab.

Do I need to use some sought of delay to make sure when DVDLab
authors the DVD ...the resulant movies will be synchonised ???

Should I subtract the audio length from the video length and
using that difference to put a delay between the audio and video
in DVDLab???

Thats .054 sec.

Another SVCD has the following results from VirtualDubMod:

Video: 41 : 42 : 834

Audio: 41 : 42 : 217

[mats.hogberg]

It depends. Try and see.
The audio stream may start later than the video stream and end at the same time as the video stream - then you'll get a (small in this case) sync problem, most easily remedied by inserting a compensating amount of silence at the beginning of the wav (GoldWave).
It may also start out correctly, just ending a bit sooner than the video stream - in that case, you won't have any problem at all.

/Mats

[johns0]

Its best to resample the audio from 44.1khz to 48khz with goldwave before encoding to ac3,i had the same problem with files going out of sync when feeding 44.1khz audio to ffmpeg to encode to ac3.

[sacajaweeda]

MPEGSource("yourSVCD.mpg")
ResampleAudio(48000)
DelayAudio(-.054)

Load that script into VDubMod and save your WAV to a new file to be converted to AC3.

That should do it.

[aussiemac]

Thanks for the advice guys...

I was talking about the output given by VirtualDubMod ...eg information
from original SVCD...

open SVCD in VirtualDubMod
then look under "streams" on menu and activate "report"

this is prior to my outputing a wav file
and then converting to 48Khz AC3

I am going to give it a go with DVDLab Pro and see what happens..

Thanks again

[aussiemac]

I authored the SVCDs with DVDLab ..and there was no real audio sync
problem that I could see...so all my worrying for nothing!

But the three suggestions sent are all things I will put in my data bank for future reference..so Thanks again guys for the help and advice!!