 	/// Pressing either volume button changes volume by 0.0625 (experimentally determined constant).
 	fileprivate static let volumeStep = 0.0625
 	
+    fileprivate static let AVAudioSessionOutputVolumeKey = "outputVolume"
+    
 	// MARK: - Init
 	
 	/// Creates a new instance of `VolumeBar`.

			}
		}
	}
	
	// MARK: - Observer callbacks
	
	/// Observe changes in volume.
	///
	/// This method is called when the user presses either of the volume buttons.

			print("VolumeBar: Initializing audio session failed.")
		}
		
        self.addVolumeBarObservers()
	}
	
	/// Stop observing changes in volume.
