I'd like to know exactly what causes audio to go out of sync.

Let's assume that during conversion processes, including framerate conversions, I know what I'm doing (in fact I do these fairly often) and that I'm doing things correctly.

Specifically, I'm wondering if it is the case that within some multiplexed formats (i.e. MPG) or "container" formats (i.e. AVI), the audio does not start off at the same time as the video. For instance, it seems that I once loaded an AVI into some NLE program or other (can't remember which right now), and there was a short empty space at the beginning of the audio track. If I were to take such an AVI and say, extract the audio to a .wav with VirtualDub, would that waveform contain a short section of emptiness at the beginning, or would it just contain the soundtrack in its actual length? If the latter is the case, then it seems that a remultiplex following encoding would result in an out-of-sync file. Does this happen? If so, what is a good way to routinely detect this characteristic before I demultiplex/reencode/whatever.

Also, specifically regarding BeSweet, why is there a default option to "Set Delay to -101 msec?" (this is in AC3Machine). I've even read a tutorial somewhere indicating that the user should leave that setting checked.

Thirdly and lastly, regarding DVD2AVI, when you save a project and decode the audio, the decoded .mpa or .wav form will often have a title which indicates a delay in milliseconds. Does this mean that the extracted audio file starts later (or earlier) than the video? And, should I then use, say, BeSweet's audio delay if I were going to convert the file to another format?

Sorry to be so verbose, but I'm really hung up on this sync issue. I thought instead of looking for a way to fix it I ought to look for a way to avoid it. For fixing audio sync, I've read that bbMPEG is a great tool for that. I use bbMPEG for multiplexing, but I have no idea how to go about using it to restore sync.

I did discover this thread on using Womble to fix MPEG files, but I sure would like to find a way to examine any pairing of files in any format, say an .m2v file with an .ac3 file, in NLE fashion ...

Tips?

-abs