Xvid encoding restrictions

I spent some time just now trying to figure out why I couldn't get VirtualDub to compress a video using the Xvid codec. The issue apparently was that the frame width and height had to be a multiple of 4 (maybe only 2, I just tried 4). This is not listed in the video format restrictions, and I feel like this used to not be the case, but also that at some point it was the case, or maybe that was just for Divx. Who knows? Anyways, if you are trying to compress a video with VirtualDub and are getting the error:

VirtualDub cannot start video compression:
An unknown error occurred (may be corrupt data)
(error code -100)

try resizing your video to be multiples of 4.