wrtc.onEarlyMedia() is called when media (sound) is received from a remote client we have called before the actual call begins. Early media is usually used to transmit the ringing sound as media instead of wrtc.onRinging()
When this event occurs you should silence any ringing sounds you might have started playing in wrtc.onRinging()
When early media (sound) is received from a client we have called before call.is("connected") returns true.
wrtc.onEarlyMedia(call)