Roll20 Web RTC Video Input Source dropdown empty, video won't work

Legacy works, but the Web RTC it encourages me to use has an empty box for video input source. I updated my browser, cleared cookies and cache. The browser is allowing the site to use the webcam, and the Legacy version (and the whole rest of the internet) can use it, but not this Web RTC. I also tested it with a second browser and same problem. Is this a known issue?

I believe that this feature is disabled unless there is another player in the game. Could this be what you are experiencing?

I did have another player there, and it still wasn't working.