The player who creates the challenge picks the format - whoever joins gets the same one automatically.
Try your camera and mic here first, without starting a match or bothering an opponent. Whichever camera you pick is remembered and used when you turn the camera on in a game.
Filled in automatically - the signaling server runs on this same address, so there's normally nothing to change here. Clear the box to go back to the automatic value. Only set this by hand if you're deliberately using a signaling server somewhere else.