I just wanted to chime in that I'm having the same problem, in this case on an iMac using Chrome. In roll20, when using chrome, it will always select my built in facetime camera, greying out the menu to select which camera. (I can switch mics fine.) This is the case even though my higher quality USB web cam is set as the default in Chrome's settings and works in hangouts. Since the facetime camera is built in, I can't simply unplug it. Clearing cache does nothing and the USB webcam is authorized and is selected as the default in general settings and site settings. Firefox allows me to select the USB camera, but the quality seems lower. It's not the biggest problem in the world, but it's the one fly in my roll20 bliss at the moment. (Edit: To be clear the WebRTC test app default selects the correct USB webcam.) (Edit again: in case it is relevant, we do happen to be using the same camera. I have a Logitech C920 as well.)