I've run a number of long tests since we spoke last with the same settings as seemed to have caused the crash, with no luck causing any instability.
The one difference is that I'm not using an MP3 audio file for the resulting video... considering that the failed video had a 1:53 audio track and that's about when the recording failed.... I'm guessing that might be the problem. It's weird because I recorded a much longer video several times before that with the same track and no problem, but hey if adding the audio in afterwards helps stability, I'm all for it!
Also, I have a small suggestion for the framing screen: it would be really helpful if that screen (and the subsequent "non-dark", mid recording screen) were to show the difference between portrait and landscape format. It's hard to tell otherwise if the recording is taking place with the correct orientation--there's no visual indication I can see.
Thanks again, and if I ever have any luck re-creating that crash, I'll fill you in!