Create AudioMixer instance.
Add audio MediaStream to be mixed, if the stream doesn't contain any audio tracks it will be ignored.
MediaStream to be mixed.
Disconnect MediaStreamAudioSourceNode and clear references.
At this point a WebAudio ChannelMergerNode is created and and the two associated MediaStreams are connected to it; the resulting mixed MediaStream is returned.
The AudioMixer, as the name implies, mixes a number of MediaStreams containing audio tracks into a single MediaStream.