Invoking getUserMedia():

1. Event mediaAccessSuccess and getUserMedia() callback success will be triggered.

1a. Event mediaAccessError is triggered if there is a failed attempt of retrieving Stream. If audioFallback is set to true in the init(), proceed to step 1b, else step 1e.
1b. Invokes getUserMedia() again to retrieve audio only Stream.
1c. After audio only Stream successfully retrieved, Event mediaAccessSuccess and getUserMedia() callback success will be triggered. Skip all steps below.
1d. Event mediaAccessError is triggered for the failed attempt of retrieving audio only Stream.
1e. getUserMedia() callback error will be triggered.