onVideoDevices = devices => {

	            if ( !devices || devices.length === 0 ) {

	                throw Error( 'no video device found' );

	            }

	            const device = targetDevice || devices[ 0 ];
	            constraints.video.deviceId = device.deviceId;

	            return getUserMedia( constraints );

	        }
Start streaming
@param {MediaDeviceInfo} [targetDevice]
@memberOf Media
@instance