   navigator.mediaDevices.enumerateDevices().then((devices) => {
                    microphoneSources.innerHTML = '';

                    // Not all environments will be able to enumerate mic labels and ids. All environments will be able
                    // to select a default input, assuming appropriate permissions.
                    var defaultOption = document.createElement('option');
                    defaultOption.appendChild(document.createTextNode('Default Microphone'));
                    