Here's some stuff on AFD.
https://en.wikipedia.org/wiki/Active_Format_Description
Pretty unlikely that "nonstandard" aspect ratios are being used, but perhaps "less-common". I would think a good DTV converter would interpret the AFD and morph it consistently as directed by your menu choices. I've not played with a lot of them, though. I do know I can't stand altered aspect ratios.
Chip