I managed to successfully encode a 1.7mb avi file and a 56.1mb avi file.
The one i'm having the segfaults with is a 348.8mb Xvid (the others were divx). Another file I had segfaults with is a 347.4mb Xvid file (both are HD quality 16:9 45-ish minute recordings), but the latter one gave me the segfault much later during the encode (it almost got the entire video done, except for the last few minutes).
I even added the -ffourcc XVID option to my script, and as you can see from my previous output post, I'm running the script as sudo (just to make sure there aren't any silly file write permission errors).
Still no go.
Any other suggestions?