将 AVAudioMixerNode 连接到 AVAudioEngine

Question

我使用 AVAudioMixerNode 来改变音频格式。条目对我帮助很大。下面的代码给了我想要的数据。但是我在 phone 的扬声器上听到了自己的声音。我该如何预防？

func startAudioEngine()
{
    engine = AVAudioEngine()

    guard let engine = engine, let input = engine.inputNode else {
        // @TODO: error out
        return
    }

    let downMixer = AVAudioMixerNode()
    //I think you the engine's I/O nodes are already attached to itself by default, so we attach only the downMixer here:
    engine.attach(downMixer)

    //You can tap the downMixer to intercept the audio and do something with it:
    downMixer.installTap(onBus: 0, bufferSize: 2048, format: downMixer.outputFormat(forBus: 0), block:  //originally 1024
        { (buffer: AVAudioPCMBuffer!, time: AVAudioTime!) -> Void in

            //i get audio data here
        }
    )

    //let's get the input audio format right as it is
    let format = input.inputFormat(forBus: 0)
    //I initialize a 16KHz format I need:
    let format16KHzMono = AVAudioFormat.init(commonFormat: AVAudioCommonFormat.pcmFormatInt16, sampleRate: 11025.0, channels: 1, interleaved: true)

    //connect the nodes inside the engine:
    //INPUT NODE --format-> downMixer --16Kformat--> mainMixer
    //as you can see I m downsampling the default 44khz we get in the input to the 16Khz I want
    engine.connect(input, to: downMixer, format: format)//use default input format
    engine.connect(downMixer, to: engine.outputNode, format: format16KHzMono)//use new audio format

    engine.prepare()

    do {
        try engine.start()
    } catch {
        // @TODO: error out
    }
}

Answer 1

您可以通过扬声器听到麦克风录音，因为您的麦克风连接到 downMixer，而 downMixer 连接到 engine.outputNode。如果您不将它与其他输入一起使用，您可能只是将 downMixer 的输出静音：

downMixer.outputVolume = 0.0

Answer 2

我这样做是为了将频率更改为 48000Hz/每个样本 16 位/2 个通道，并将其保存到波形文件中：

      let outputAudioFileFormat = [AVFormatIDKey: Int(kAudioFormatLinearPCM), AVSampleRateKey: 48000, AVNumberOfChannelsKey: 2, AVEncoderAudioQualityKey: AVAudioQuality.high.rawValue]
      let audioRecordingFormat : AVAudioFormat = AVAudioFormat.init(commonFormat: AVAudioCommonFormat.pcmFormatInt16, sampleRate: 48000, channels: 2, interleaved: true)!

      do{
           try file = AVAudioFile(forWriting: url, settings: outputAudioFileFormat, commonFormat: .pcmFormatInt16, interleaved: true)

           let recordingSession = AVAudioSession.sharedInstance()

           try recordingSession.setPreferredInput(input)
           try recordingSession.setPreferredSampleRate(audioRecordingFormat.sampleRate)

           engine.inputNode.installTap(onBus: 0, bufferSize: 1024, format: audioRecordingFormat, block: self.bufferAvailable)
           engine.connect(engine.inputNode, to: engine.outputNode, format: audioRecordingFormat) //configure graph
      }
      catch
      {
           debugPrint("Could not initialize the audio file: \(error)")
      }

和功能块

 func bufferAvailable(buffer: AVAudioPCMBuffer, time: AVAudioTime)
 {
      do
      {
           try self.file?.write(from: buffer)

           if self.onBufferAvailable != nil {
                DispatchQueue.main.async {
                     self.onBufferAvailable!(buffer) // outside function used for analyzing and displaying a wave meter
                }
           }
      }
      catch{
           self.stopEngine()

           DispatchQueue.main.async {
                self.onRecordEnd(false)
           }
      }
 }

stopEngine函数就是这个，你想停止录音的时候也应该调用它：

 private func stopEngine()
 {
      self.engine.inputNode.removeTap(onBus: 0)
      self.engine.stop()
 }

将 AVAudioMixerNode 连接到 AVAudioEngine

Connecting AVAudioMixerNode to AVAudioEngine

pcm

ios

swift

avaudioengine