相关疑难解决方法(0)

我在对从麦克风中提取的音频进行下采样时遇到问题。我正在使用 AVAudioEngine 通过以下代码从麦克风中获取样本：

assert(self.engine.inputNode != nil)
let input = self.engine.inputNode!

let audioFormat = AVAudioFormat(commonFormat: .pcmFormatFloat32, sampleRate: 8000, channels: 1, interleaved: false)    
let mixer = AVAudioMixerNode()
engine.attach(mixer)
engine.connect(input, to: mixer, format: input.inputFormat(forBus: 0))

do {
    try engine.start()

    mixer.installTap(onBus: 0, bufferSize: 1024, format: audioFormat, block: {
            (buffer: AVAudioPCMBuffer!, time: AVAudioTime!) -> Void in
        //some code here
    })

} catch let error {
    print(error.localizedDescription)
}

此代码在 iPhone 5s 上运行良好，因为麦克风输入为 8000Hz，并且缓冲区填充了来自麦克风的数据。

问题是我希望能够从 iPhone 6s（及更高版本）录制麦克风以 16000Hz 录制的内容。奇怪的是，如果我将 mixernode 与引擎 mainmixernode 连接起来（使用以下代码）：

engine.connect(mixer, to: mainMixer, format: …

我使用 AVAudioMixerNode 来更改音频格式。这篇文章对我帮助很大。下面的代码给了我我想要的数据。但我在电话扬声器中听到了自己的声音。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: …