I finally figured out the fix for the problem I’ve been having using avconv and ffmpeg to capture from my webcam via Video4Linux2! That issue, of course, was that it would hang the session hard and not release its lock on the webcam.
It seems that if you force V4L1 compatibility, the issue goes away entirely. I posted the exact preload command over in the ScreenStudio Google+ Community.
It’s odd that the exact same problem afflicts the built-in webcam as well as the logitech external USB cam I tested. I suppose that’s why it took me all this time to narrow it down.