Alamofire音频下载，无法播放下载的音频

Question

我是编程和swift的新手，我从服务器下载音频文件时遇到问题，这是我的代码：

var player: AVAudioPlayer?

func downloadSong()
{
    let destination = DownloadRequest.suggestedDownloadDestination(for: .documentDirectory)
    let url = "https://link for DWNL music"
    print("DESTINATION \(destination)")

    Alamofire.download(
        url,
        method: .get,
        parameters: nil,
        encoding: JSONEncoding.default,
        headers: nil,
        to: destination).downloadProgress(closure: { (progress) in
            //progress closure
        }).response(completionHandler: { (DefaultDownloadResponse) in
            let destinationUrl = DefaultDownloadResponse.destinationURL
            print("Downloaded file to \(DefaultDownloadResponse.destinationURL!)")

            do {
                self.player = try AVAudioPlayer(contentsOf: destinationUrl!)

                guard let player = self.player else {  return }
                player.delegate = self
                player.prepareToPlay()
                player.play()
            } catch let error {
                print(error.localizedDescription)
            }

        })
}

它通过了所有代码，但没有播放任何内容...请告诉我这里我做错了什么。我对保存文件有疑问，我认为错误就在那里。谢谢！