wrtc.adv.createLoopBackCall() is used to start a local call (client calling itself). Usually it is used to measure local microphone volume.
Once started volume information will be reported using wrtc.onVolume() events.
As wrtc.adv.volumeMeter() only works when a call is in progress a local loopback call can be started to create a special call that can be used for microphone volume measurements.
The local loopback call will not be included in wrtc.getCall(), wrtc.getCalls() and similar lists of active calls.
wrtc.adv.createLoopBackCall(video, volume):
Usually you call wrtc.adv.createLoopBackCall() without any arguments and it will then start an audio only local loopback call and start measuring its microphone volume.
Nothing.
wrtc.onVolume() events reporting current audio volume.