start
Starts monitoring the local audio level.
Once started, a CallClientListener.onLocalAudioLevel event will be emitted containing the latest audio level information at the specified frequency, which can be up to every 100ms. If no frequency is specified, a default frequency of 200ms is used.
The optional callback (listener) will be invoked either when the operation has completed, or if it encounters an error.
Errors will also be provided to the CallClientListener.onError callback.