Alright, here's an update.
Looks like 2 of the 3 trendnet's have a sporadic issue with the JPEG feed. Anywhere from immediately after a camera reboot, to a day later, the jpeg feed stops working. This happens even when I access the URL directly from a web browser. I've reported the issue to TrendNet, not sure what will come of that.
I switched the IP-312 and IP-312W back to the MJPEG feed, but instead of using http://[IP]/cgi/mjpg/mjpg.cgi, I've been using http://[IP]/cgi/mjpg.cgi, which seems to have been working well. Just to test, I switched back to the original URL http://[IP]/cgi/mjpg/mjpg.cgi, and the original issue occured again.
I noticed, however that the 'new' MJPEG url doesn't have audio. Can you add this to your list, and create a new build for me to test with?
Thanks!