Well, in any case, it seemed to work. I left a batch encode of several files running overnight on the Mac and in the morning it was done, no crashes.

So, on the mac, the solution is: Delete all Divx. Thanks for the help, and the tip about that one set of files that I hadn't seen before.

I'd still eventually like to find a PC solution, since the PC can do these encodes about four times as fast (when it doesn't crash).

Unfortunately, when the PC crashes, it crashes HARD, with the system simply going BLINK straight into full-power-off mode. One millisecond it's working, the next, bam, no power. No blue screen, no crash message, no log file. So I'm not sure how to go about finding the source of the crash.

For all I know, it could still be some leftover remnant of Divx on the PC that I'm not seeing, but I wouldn't know where to look other than Gspot and the Windows control panel codecs list.