How to get the sound played in the app？

In the app there is a webview which is a web game with sound and video

@IBOutlet var webView: WKWebView!
webView.navigationDelegate = self
let url=URL(string: "https://www.crazygames.com/game/tap-tap-shots")
webView.load(URLRequest(url: url!))

I use RPScreenRecorder

import ReplayKit
import UIKit

class ViewController: UIViewController, RPPreviewViewControllerDelegate {
    override func viewDidLoad() {
        super.viewDidLoad()

        navigationItem.rightBarButtonItem = UIBarButtonItem(title: "Start", style: .plain, target: self, action: #selector(startRecording))
    }

    @objc func startRecording() {
        let recorder = RPScreenRecorder.shared()

        recorder.startRecording{ [unowned self] (error) in
            if let unwrappedError = error {
                print(unwrappedError.localizedDescription)
            } else {
                self.navigationItem.rightBarButtonItem = UIBarButtonItem(title: "Stop", style: .plain, target: self, action: #selector(self.stopRecording))
            }
        }
    }

    @objc func stopRecording() {
        let recorder = RPScreenRecorder.shared()

        recorder.stopRecording { [unowned self] (preview, error) in
            self.navigationItem.rightBarButtonItem = UIBarButtonItem(title: "Start", style: .plain, target: self, action: #selector(self.startRecording))

            if let unwrappedPreview = preview {
                unwrappedPreview.previewControllerDelegate = self
                self.present(unwrappedPreview, animated: true)
            }
        }
    }

    func previewControllerDidFinish(_ previewController: RPPreviewViewController) {
        dismiss(animated: true)
    }
}

Can record video, but no sound from webpage