同步AVAudioPlayerNode和AVAudioEngine录音开始

Question

同步AVAudioPlayerNode和AVAudioEngine录音开始

5

我使用 AVAudioEngine 来播放和录制音频。对于我的使用场景，我需要在开始录制音频时立即播放声音。目前，我的录制似乎是在声音播放之前开始的。如何使声音和录音同时开始？理想情况下，我希望录制和声音可以同时开始，而不是在后期进行同步。

以下是我的代码：

class Recorder {
  enum RecordingState {
    case recording, paused, stopped
  }
  
  private var engine: AVAudioEngine!
  private var mixerNode: AVAudioMixerNode!
  private var state: RecordingState = .stopped
    
    

  private var audioPlayer = AVAudioPlayerNode()
  
  init() {
    setupSession()
    setupEngine()
    
  }
    
    
  fileprivate func setupSession() {
      let session = AVAudioSession.sharedInstance()
    try? session.setCategory(.playAndRecord, options: [.mixWithOthers, .defaultToSpeaker])
      try? session.setActive(true, options: .notifyOthersOnDeactivation)
   }
    
    fileprivate func setupEngine() {
      engine = AVAudioEngine()
      mixerNode = AVAudioMixerNode()

      // Set volume to 0 to avoid audio feedback while recording.
      mixerNode.volume = 0

      engine.attach(mixerNode)

    engine.attach(audioPlayer)
        
      makeConnections()

      // Prepare the engine in advance, in order for the system to allocate the necessary resources.
      engine.prepare()
    }

    
    fileprivate func makeConnections() {
       
      let inputNode = engine.inputNode
      let inputFormat = inputNode.outputFormat(forBus: 0)
        print("Input Sample Rate: \(inputFormat.sampleRate)")
      engine.connect(inputNode, to: mixerNode, format: inputFormat)
      
      let mainMixerNode = engine.mainMixerNode
      let mixerFormat = AVAudioFormat(commonFormat: .pcmFormatFloat32, sampleRate: inputFormat.sampleRate, channels: 1, interleaved: false)
    
      engine.connect(mixerNode, to: mainMixerNode, format: mixerFormat)

      let path = Bundle.main.path(forResource: "effect1.wav", ofType:nil)!
      let url = URL(fileURLWithPath: path)
      let file = try! AVAudioFile(forReading: url)
      audioPlayer.scheduleFile(file, at: nil)
      engine.connect(audioPlayer, to: mainMixerNode, format: nil)
        
        }
    
    
    //MARK: Start Recording Function
    func startRecording() throws {
        print("Start Recording!")
      let tapNode: AVAudioNode = mixerNode
      let format = tapNode.outputFormat(forBus: 0)

      let documentURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0]
        
      // AVAudioFile uses the Core Audio Format (CAF) to write to disk.
      // So we're using the caf file extension.
        let file = try AVAudioFile(forWriting: documentURL.appendingPathComponent("recording.caf"), settings: format.settings)
       
      tapNode.installTap(onBus: 0, bufferSize: 4096, format: format, block: {
        (buffer, time) in

        try? file.write(from: buffer)
        print(buffer.description)
        print(buffer.stride)
       
        //Do Stuff
        print("Doing Stuff")
      })
    
      
      try engine.start()
        audioPlayer.play()
      state = .recording
    }
    
    
    //MARK: Other recording functions
    func resumeRecording() throws {
      try engine.start()
      state = .recording
    }

    func pauseRecording() {
      engine.pause()
      state = .paused
    }

    func stopRecording() {
      // Remove existing taps on nodes
      mixerNode.removeTap(onBus: 0)
      
      engine.stop()
      state = .stopped
    }
    

    
    
}

- coder

不幸的是（也许令人惊讶的是），我认为没有一种准确的方法可以在不测量的情况下确定延迟。 - sbooth

@sbooth 我该如何测量延迟？ - coder

最理想的方法是使用环回电缆，将设备的输出连接到其输入。您可以向输出发送测试信号，记录发送时间，然后检测输入中的相同信号。时间差就是往返延迟。虽然有一些使用 AVAudioEngine 进行估算的方法，但在我的实验中，没有一种是样本精确的。 - sbooth

嗯...我可以这样做，但如果用户降低音量会怎么样呢？这会使检测输出信号变得困难。如果您知道使用 AVAudioEngine 估计往返延迟的方法，请在回答中分享它们。大致估算总比什么都不知道好！ - coder

这里有一些关于https://dev59.com/oFEG5IYBdhLWcg3wdufF的讨论。 - sbooth

1个回答

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- Moose · Answer 1

你试过在安装tap之前启动播放器吗？

// Stop the player to be sure the engine.start calls the prepare function
audioPlayer.stop()
try engine.start()
audioPlayer.play()
state = .recording

tapNode.installTap(onBus: 0, bufferSize: 4096, format: format, block: {
        (buffer, time) in
        try? file.write(from: buffer)
      })

如果在这种情况下，您的录制稍晚一些，可以尝试使用player.outputPresentationLatency进行补偿。根据文档，这是一个最大值。意味着时间可能略低于此值。我希望这值得一试。

print(player.outputPresentationLatency)
// 0.009999999776482582

let nanoseconds = Int(player.outputPresentationLatency * pow(10,9))
let dispatchTimeInterval = DispatchTimeInterval.nanoseconds(nanoseconds)
            
player.play()
DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + dispatchTimeInterval) {
    self.installTap()
    self.state = .recording
}