I have a Divx AVI. When I open it up in VDub, and step through it frame by frame, it is "progressive looking". In other words, there is no evidence of interlacing.

But, when I use this AVI as a source in TMPGEnc, TMPGEnc wastes a lot of time "Judging Field Order", and then identifies the source as "interlaced".

This is quite confusing. I realize that progressive frames could always be divided into fields and then "physically" stored (and encoded) on a field by field basis. Is that what is going on here?

And how come it is only when I use the wizard that TMPGEnc does the "judging field order". In non-wizard mode, it seems to be able to instantly identify the source!