如何停止AkPlaygroundLoop，它会不断循环播放

Question

我的播放器将islooping设置为 false ，但是循环不断循环，有人知道如何停止它吗？

我希望音频结束后停止播放。

do{
     let audioFileName = getDocDirectory().appendingPathComponent(filename)
     print ("\(audioFileName)")
     let file = try AKAudioFile(forReading: audioFileName)
     let player = AKPlayer (audioFile:file)
     player.isLooping = false
     let tracker = AKFrequencyTracker(player)
     AudioKit.output = tracker
     try AudioKit.start()
     player.play()
     AKPlaygroundLoop(every: 0.1) {
         print(tracker.frequency)
         //keeps printing frequency infinitely 
     }
}
catch
{
    print(error)
}