This error indicates that even if access to the microphone was successful
was called successfully) the browser microphone input was zero, probably because the user has muted the microphone,
or due to some other browser-access-to-microphone related problem. You may prompt the user to unmute the microphone.
Moreover, sometimes microphone related problems can be resolved by simply restarting the browser, thus you may as well
prompt the user to restart his browser and try again.