如何让 AVAudioEngine 从麦克风输出 PCM-16？

Question

我正在使用AVAudioEngine，我试图让它以 16000Hz 的频率输出.pcmFormatInt16，但我似乎无法让它工作。这就是我正在做的事情：

let audioEngine = AVAudioEngine()
let mixer = AVAudioMixerNode()
let input = self.audioEngine.inputNode!

audioEngine.attach(mixer)
audioEngine.connect(input, to: mixer, format: input.outputFormat(forBus: 0))

let recordingFormat = AVAudioFormat(commonFormat: .pcmFormatInt16, sampleRate: 16000.0, channels: 1, interleaved: true)

mixer.installTap(onBus: 0, bufferSize: 2048, format: recordingFormat) { [weak self] (buffer, _) in
    // buffer here is all 0's!
}

self.audioEngine.prepare()
try! self.audioEngine.start()

如上所述，当我访问缓冲区时，它总是全为 0，静默。

Answer 1

AVAudioEngine 不支持更改采样率。 你可以使用 AVAudioConverter 来改变采样率

let inputFormat = input.outputFormat(forBus: 0)
let recordingFormat = AVAudioFormat(commonFormat: .pcmFormatInt16, sampleRate: 16000.0, channels: 1, interleaved: true)
converter = AVAudioConverter(from: inputFormat, to: recordingFormat)

mixer.installTap(onBus: 0, bufferSize: 2048, format: inputFormat) { [weak self] (buffer, _) in
    let convertedBuffer = self?.converter.convertBuffer(additionalBuffer: buffer)
}