how to detect volumn change in action extension

I want to make a youtube player using action extension.But the problem is volumn changes won't be reflected in an action extension while it works in an app.

my code is like:

let audioSession = AVAudioSession.sharedInstance()

self.obs = audioSession.observe(\.outputVolume ) {[weak self] (av, change) in

     guard let self = self else { return }

     print("volume \(av.outputVolume)")

     self.slide.value = av.outputVolume
}

and also I tried to hide the system volumn bar using code like this:

let volumeView = MPVolumeView(frame: CGRect(x: 0, y: 0, width: 0, height: 0))
self.view.addSubview(volumeView)

it also works in an app but not in an action extension. Anybody can help me out? Or tell me why they won't work in an action extension?