问AVPlayerViewController拒绝加载/播放视频文件/流

EN

import UIKit
import AVKit
import AVFoundation

private var playerContext = 0

class PlayerViewController: AVPlayerViewController {    
    override func awakeFromNib() {
        print("awake!")

        let URL = NSURL(string: "http://live-lh.daserste.de/i/daserste_de@91204/index_2692_av-b.m3u8")!
        let player = AVPlayer(URL: URL)
//      player.addObserver(self, forKeyPath: "status", options: [.Old, .New], context: &playerContext) // commented out for testing purposes, doesn't make any difference

        self.player = player
        self.showsPlaybackControls = true
    }

    override func observeValueForKeyPath(keyPath: String?, ofObject object: AnyObject?, change: [String : AnyObject]?, context: UnsafeMutablePointer<Void>) {
        if context == &playerContext {
            print("\(keyPath!): \(change!)")
        } else {
            super.observeValueForKeyPath(keyPath, ofObject: object, change: change, context: context)
        }
    }

    // viewDidLoad() and didReceiveMemoryWarning()
}