将流式 u-law 转换为 PCM 听起来很金属

如何解决将流式 u-law 转换为 PCM 听起来很金属

我有一个语音流应用，它通过网络套接字接收实时音频，编码为 G.711 u-law 8KHz 单声道，我想使用 AVAudioEngine 播放。

为此，我使用 AVAudioConverter 将音频样本转换为具有相同采样率和音频参数的 PCM (Float32)。

出于某种原因，我听到的声音是金属和回声。

这是我的代码：

class AudioEngine {
    private var engine: AVAudioEngine!
    
    // Audio player
    private var playerNode: AVAudioPlayerNode!
    private let playerFormat = AVAudioFormat(commonFormat: .pcmFormatFloat32,sampleRate: 8000,channels: 1,interleaved: false)

    // AudioConverter properties
    private var inputConverter: AVAudioConverter? // audioIn (Player)
    
    private lazy var inputDescriptor = AudioStreamBasicDescription(mSampleRate: 8000,mFormatID: kAudioFormatULaw,mFormatFlags: 0,mBytesPerPacket: 1,mFramesPerPacket: 1,mBytesPerFrame: 1,mChannelsPerFrame: 1,mBitsPerChannel: 8,mReserved: 0)
    private var inputFormat: AVAudioFormat?
    
    init() {
        engine = AVAudioEngine()
        setupPlayerFormats()
        setupSession()
        setupPlayer()
    }
    
    deinit {
        stopStream()
    }
    
    func playStream() throws {
        guard !engine.isRunning else {
            print("engine is running")
            return
        }
        try engine.start()
        playerNode.play()
        print("playing stream")
    }
    
    func stopStream() {
        playerNode.stop()
        engine.stop()
    }
    
    /// each byte of kAudioFormatULaw is converted to 4 bytes of pcmFormatFloat32
    func convertAudio(data: Data) {
        guard let sourceFormat = inputFormat,let targetFormat = playerFormat,let dataBuffer = data.makePCMBuffer(format: sourceFormat),let pcmBuffer = AVAudioPCMBuffer(pcmFormat: targetFormat,frameCapacity: dataBuffer.frameLength) else {
            fatalError("Unable to set audio player converter formats")
        }
        do {
            try inputConverter?.convert(to: pcmBuffer,from: dataBuffer)
        } catch let error as NSError {
            print("audioIn (Player) Conversion error=\(error)")
        }
        let audioBufferSize = pcmBuffer.audiobufferlist.pointee.mBuffers.mDataByteSize
        if audioBufferSize > 0 {
            self.playerNode.scheduleBuffer(pcmBuffer,completionHandler: nil)
        }
    }
    

private extension AudioEngine {  
    func setupPlayerFormats() {
        inputFormat = AVAudioFormat(streamDescription: &inputDescriptor)
        guard let source = inputFormat,let output = playerFormat else {
            fatalError("Unable to set audio player formats")
        }
        inputConverter = AVAudioConverter(from: source,to: output)
    }
    
    func setupSession() {
        let session = AVAudioSession.sharedInstance()
        do {
            try session.setCategory(.playAndRecord,mode: .voiceChat)
            try session.setActive(true,options: .notifyOthersOnDeactivation)
        } catch let error as NSError {
            fatalError("Unable to setup audio session with error=\(error)")
        }
    }
    
    func setupPlayer() {
        playerNode = AVAudioPlayerNode()
        
        engine.attach(playerNode)
        engine.connect(playerNode,to: engine.mainmixerNode,format: playerFormat)
    }
}

每次我从 websocket 接收音频数据时都会调用

func convertAudio(data: Data)。

我想知道我的音频转换代码是否不正确，或者是否有更好的解决方案来解决这个问题，希望得到任何建议。