问AVAssetResourceLoaderDelegate从未调用过

EN

import UIKit
import AVKit
import AVFoundation

class ViewController: UIViewController, AVAssetResourceLoaderDelegate 
    var player: AVPlayer!
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    override func viewDidAppear(_ animated: Bool) {
        let videoURL = URL(string: "https://devstreaming-cdn.apple.com/videos/streaming/examples/img_bipbop_adv_example_ts/master.m3u8")
        let asset = AVURLAsset(url: videoURL! as URL, options: nil)
        asset.resourceLoader.setDelegate(self, queue: DispatchQueue.main)
        let item = AVPlayerItem(asset: asset)
        let player = AVPlayer(playerItem: item)
        let playerViewController = AVPlayerViewController()
        playerViewController.player = player
        self.present(playerViewController, animated: true) {
            playerViewController.player!.play()
        }

    }


    func resourceLoader(_ resourceLoader: AVAssetResourceLoader, shouldWaitForLoadingOfRequestedResource loadingRequest: AVAssetResourceLoadingRequest) -> Bool {

        NSLog("This method is never called")

        return true
    }


}