Audio delay when splitting

[MrDarcy]

Hi, sorry if this is a FAQ, but I haven't found it.

I muxed audio e video into an .avi setting delay to -63 because this is what DVD2AVI reported. Now it's in-sync.

Now I have to split the file in two parts, so I'll use direct stream copy from the source file both for video and audio, but what about the audio delay?
Do I have to set it to -63 again?

I suppose I don't, but does this mean the audio delay setting is relative to the previously used delay when I keep the source audio, while it's an absolute delay when I mux an external WAV?

Thanks :-)

[Asmodian]

I believe you could think of it like that :)

I think of it as once the audio is muxed in it doesn't have a delay, but is just in the right place. If you demux the audio and then mux it back in without a delay is it out of sync or is it correct? (this might need to be tried with a delay that makes it very out of sync for the first mux and then seeing if the second mux gets it back to mostly in sync.

[MrDarcy]

Ok, thanks.
I will make an out-of-sync avi to test how it works !!

[Asmodian]

Please tell us your results :)

[MrDarcy]

Originally posted by Asmodian

I think of it as once the audio is muxed in it doesn't have a delay, but is just in the right place. If you demux the audio and then mux it back in without a delay is it out of sync or is it correct?

It's correct!

I did the following test (closing and reopening Vdub after each step):

1. started with separate video and audio files (from a DVD with no delay)
2. cut off 2 seconds from the beginning of the audio
3. muxed without delay --> terribly out-sync (:D )
4. muxed with delay +2000 --> new avi in-sync
5. extracted 2 minutes from the middle of new avi --> still in-sync
6. saved a wav file from the avi built at step 4.
7. remuxed the original video with the extracted wav --> still in-sync

I searched for a reference point (a door closing) in the wav created at step 6. and I found it at the same offset as in the original audio.
It seems that at step 4 Vdub added 2 seconds of silence at the beginning of the audio and from now on the audio is correct. I can split and join without having to worry about delay.

Bye!

[alexnoe]

It seems that at step 4 Vdub added 2 seconds of silence at the beginning of the audio There is no other possibility anyways...

[MrDarcy]

Yes, of course it's logical.

But in my ignorance I supposed another solution: that VDub (and AVI-MUX too) would only offset the audio beginning within the AVI padding the delay with some kind of "null" data. Now I know this is not true.

Where can I find a (simple) description about how data are stored within an AVI file?

Bye!

[alexnoe]

Unfortunately, it is not simple enough to write a simple explanation, at least not for Open-DML AVI...you find not-so-simple descriptions on www.wotsit.org.