This demo is out-dated i.e. deprecated (written in 2013).
Please try other demos: https://github.com/muaz-khan/RTCMultiConnection
This demo is using RTCMultiConnection.js. This demo enumerates over all available video devices, and appends <button> for each device. You can click any button to capture relevant webcam. Then you can click "Broadcast All Cameras" button to broadcast your "multiple-cameras" over multiple users.