AC3 and Audio delay - what does it mean?

[Bizuser]

I'm converting a DVD from PAL to NTSC. I normally use the methodology that 'slows down' the video slightly, from 25 to 23.97 fps, and slow down the audio accordingly. Works great.

Well today I'm working on a DVD that has a great soundtrack and I don't want to slow the sound down even slightly, so I'm using the 'other method' (from xesdeeni) which converts frame rate, retaining the exact duration of the audio and video.

I did the project first by decoding in DVD2AVI to PCM audio (.WAV files), and all was well, but the audio files are too big. I want to give more bandwitdth to video. So I demuxed the audio to an .AC3 file. But when I demux to AC3, there is a 'DELAY' factor built into the filename.

If I recombine the audio and video (after frame-rate converting the video, exactly the same duration), in TMPGEnc DVD Author (TDA), do I need to take this delay into account, or is that 'automatic' in some way?

Do I need to run AC3Delay to correct/remove this delay? If I don't need to, but do it, then I'm going to make matters worse. So it occured to me, what is the meaning of this delay, why is it there, and what does it mean? Why is it present in the AC3 filename but not the 'WAV' filename?

I took a wild guess and ... ignored it. I don't seem to notice anything, but I'm not sure.

So if I ignore it, and re-mux in TDA, does TDA 'allow' for the delay? If I should not ignore it, is AC3Delay the best way to deal with it?

[Gurm]

You want to... re-encode the AC3? Is it multichannel?

Last time I fiddled with this (admittedly a year ago) there were precious few (read: exactly one) programs that would work with multichannel AC3 audio.

[Bizuser]

Actually, I decoded the DVD audio (which was AC3 originally) to .wav (PCM) first, because I used TMPGEnc to do the re-encoding of the video, and decided to use it to cut the movie in 'half' at the same time. So I ended up with two .wav files. I then ran out of space on the target DVD, so decided to re-encode back to AC3, using BeSweet, which did a great job.

So I got my specific 'project' done, now I'm simply trying to learn about AC3 and the delay 'for the next time'. Lots of people seem to ask about it, and everyone gets answers to specific situations, but I never see a good explanation.

In reality, I got lucky in this project - the delay was only 8ms anyway, but I've seem much larger delays in the past.