MPVolumeView is a class from MediaPlayer framework in iOS. Used to present the user with a slider control for setting the system audio output volume, and a button for choosing the audio output route.
When first displayed, the slider’s position reflects the current system audio output volume. As the user drags the slider, the changes update the volume. If the user presses the device volume buttons while sound is playing, the slider moves to reflect the new volume.
If there is an Apple TV or other AirPlay-enabled device in range, the route button allows the user to choose it. If there is only one audio output route available, the route button is not displayed.
When an audio output route that does not support volume control, such as A2DP, is active, the volume slider is replaced with the route name.