如何在启动应用程序后取消静音？

Question

我在应用的背景上遇到了一些视频问题。

这是我的程序代码：

import UIKit
import AVKit
import AVFoundation

class IntroViewController: UIViewController {

var player: AVPlayer?

override func viewDidLoad() {
    super.viewDidLoad()

    let videoURL: NSURL = NSBundle.mainBundle().URLForResource("intro", withExtension: "mov")!

    player = AVPlayer(URL: videoURL)
    player?.actionAtItemEnd = .None
    player?.muted = false

    let playerLayer = AVPlayerLayer(player: player)
    playerLayer.videoGravity = AVLayerVideoGravityResizeAspectFill
    playerLayer.zPosition = -1

    playerLayer.frame = view.frame

    view.layer.addSublayer(playerLayer)

    player?.play()

    NSNotificationCenter.defaultCenter().addObserver(self,
        selector: "loopVideo",
        name: AVPlayerItemDidPlayToEndTimeNotification,
        object: nil)
 }

func loopVideo() {
    player?.seekToTime(kCMTimeZero)
    player?.play()
}

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

}

启动我的程序后，音乐应用程序静音。我该如何解决？

还有一个问题：从主屏幕返回此屏幕后，如果没有关闭应用程序，视频会停止。问题在哪里？