如何循环播放正在反向播放的AVPlayer？

Question

我正在使用AVPlayer播放mp3文件。我使用它而不是AVAudioPlayer，因为它支持以0.0 ... 2.0范围之外的速度播放。但是，我希望音频不断循环播放，因此我正在使用AVQueuePlayer和AVPlayerLooper播放文件。当rate属性为正时，此方法有效，但是当反向回放到达文件的开头时，它只是停止，而不是返回文件末尾并继续反向播放。有什么方法可以让播放器循环播放？这是我正在尝试的内容：

 override func viewDidLoad() {
    super.viewDidLoad()

    //Initialize the audio file and audio player

    guard let path = Bundle.main.path(forResource: "sideAMusic.mp3", ofType: nil) else {
        Console.log("Uh oh - no path could be found for filename: \("sideAMusic")")
        return
    }
    let url = URL(fileURLWithPath: path)
    let playerItem = AVPlayerItem(url: url)
    self.sideAPlayer = AVQueuePlayer(playerItem: playerItem)
    sideALooper = AVPlayerLooper(player: sideAPlayer!, templateItem: playerItem)
    sideAPlayer?.volume = 1
    sideAPlayer?.play()
}

// Use a slider in the range of -4 ... 4 to set the playback speed
@IBAction func speedSlider(_ sender: UISlider) {
    self.sideAPlayer?.rate = sender.value
}

Answer 1

您应该添加一个定期的时间观察者。这是文档的link。

您还应该检查here如何观察时间。

另外，这是一个代码示例。

    func addPeriodicTimeObserver() {
        // Notify every 0.05 second
        let timeScale = CMTimeScale(NSEC_PER_SEC)
        let time = CMTime(seconds: 0.05, preferredTimescale: timeScale)

        timeObserverToken = player.addPeriodicTimeObserver(forInterval: time,
                                                          queue: .main) {
            [weak self] currentTime in
              if CMTimeCompare(currentTime, CMTime.zero) == 0 {
                   //The track reached the beginning, you should seek player to the end time
                   self?.player.seek(to: self?.playerItem.duration, toleranceBefore: .zero, toleranceAfter: .zero)
                   self?.player.play()
              }
        }
    }

    func removePeriodicTimeObserver() {
        if let timeObserverToken = timeObserverToken {
            player.removeTimeObserver(timeObserverToken)
            self.timeObserverToken = nil
        }
    }