在 iOS 中播放原始 PCM 数据缓冲区时音频失真

Question

我正在尝试使用 iOS 中的音频单元播放音频缓冲区。音频缓冲区来自 C 库，它从 Playstation 4 接收音频并使用 Opus 对其进行解码。音频缓冲区的格式是 PCM int16_t.

有了音频单元和 TPCircularBuffer，我就可以播放声音了。不过变形严重，不干净

这是我的音频单元的设置 class

init() {
    _TPCircularBufferInit(&buffer, 960
                          , MemoryLayout<TPCircularBuffer>.size)
    setupAudio()
}

func play(data: NSMutableData) {
    TPCircularBufferProduceBytes(&buffer, data.bytes, UInt32(data.length))
}

private func setupAudio() {
    do {
        try AVAudioSession.sharedInstance().setActive(true, options: [])
    } catch { }
    
    var audioComponentDesc = AudioComponentDescription(componentType: OSType(kAudioUnitType_Output),
                                                       componentSubType: OSType(kAudioUnitSubType_RemoteIO),
                                                       componentManufacturer: OSType(kAudioUnitManufacturer_Apple),
                                                       componentFlags: 0, componentFlagsMask: 0)
    let inputComponent = AudioComponentFindNext(nil, &audioComponentDesc)
    status = AudioComponentInstanceNew(inputComponent!, &audioUnit)
    
    if status != noErr {
        print("Audio Component Instance New Error \(status.debugDescription)")
    }
    
    var audioDescription = AudioStreamBasicDescription()
    audioDescription.mSampleRate = 48000
    audioDescription.mFormatID = kAudioFormatLinearPCM
    audioDescription.mFormatFlags = kAudioFormatFlagIsPacked | kAudioFormatFlagIsSignedInteger
    audioDescription.mChannelsPerFrame = 2
    audioDescription.mFramesPerPacket = 1
    audioDescription.mBitsPerChannel = 16
    audioDescription.mBytesPerFrame = (audioDescription.mBitsPerChannel / 8) * audioDescription.mChannelsPerFrame
    audioDescription.mBytesPerPacket = audioDescription.mBytesPerFrame * audioDescription.mFramesPerPacket
    audioDescription.mReserved = 0
    status = AudioUnitSetProperty(audioUnit, kAudioUnitProperty_StreamFormat,
                                  kAudioUnitScope_Input, 0, &audioDescription,
                                  UInt32(MemoryLayout<AudioStreamBasicDescription>.size))
    
    if status != noErr {
        print("Enable IO for playback error \(status.debugDescription)")
    }
    
    var flag: UInt32 = 0
    status = AudioUnitSetProperty(audioUnit, kAudioOutputUnitProperty_EnableIO,
                                  kAudioUnitScope_Input, 1, &flag,
                                  UInt32(MemoryLayout.size(ofValue: flag)))
    
    if status != noErr {
        print("Enable IO for playback error \(status.debugDescription)")
    }
    
    var outputCallbackStruct = AURenderCallbackStruct()
    outputCallbackStruct.inputProc = performPlayback
    outputCallbackStruct.inputProcRefCon = UnsafeMutableRawPointer(Unmanaged.passUnretained(self).toOpaque())
    status = AudioUnitSetProperty(audioUnit, kAudioUnitProperty_SetRenderCallback,
                                  kAudioUnitScope_Global, 0, &outputCallbackStruct,
                                  UInt32(MemoryLayout<AURenderCallbackStruct>.size))
    status = AudioUnitInitialize(audioUnit)
    if status != noErr {
        print("Failed to initialize audio unit \(status!)")
    }
    status = AudioOutputUnitStart(audioUnit)
    if status != noErr {
        print("Failed to initialize output unit \(status!)")
    }
}

播放功能

private func performPlayback(clientData: UnsafeMutableRawPointer,_ ioActionFlags: UnsafeMutablePointer<AudioUnitRenderActionFlags>, inTimeStamp: UnsafePointer<AudioTimeStamp>,
                         inBufNumber: UInt32, inNumberFrames: UInt32, ioData: UnsafeMutablePointer<AudioBufferList>?) -> OSStatus {
let player = Unmanaged<AudioPlayer>.fromOpaque(UnsafeRawPointer(clientData)!).takeUnretainedValue()
let buffer = ioData![0].mBuffers
let bytesToCopy = ioData![0].mBuffers.mDataByteSize
var bufferTail: UnsafeMutableRawPointer?
var availableBytes: UInt32 = 0
bufferTail = TPCircularBufferTail(&player.buffer, &availableBytes)
let bytesToWrite = min(bytesToCopy, availableBytes)
memcpy(buffer.mData, bufferTail, Int(bytesToWrite))
TPCircularBufferConsume(&player.buffer, bytesToWrite)
return noErr}

这里是我调用play函数的地方

private func StreamAudioFrameCallback(buffers: UnsafeMutablePointer<Int16>?,
                                  samplesCount: Int, user: UnsafeMutableRawPointer?) {
let decodedData = NSMutableData()
if let buffer = buffers, samplesCount > 0 {
    let decodedDataSize = samplesCount * MemoryLayout<opus_int16>.size
    decodedData.append(buffer, length: decodedDataSize)
    AudioPlayer.shared.play(data: decodedData)
}

有人熟悉这个吗？任何帮助表示赞赏。

Answer 1

您可能不想开始播放，直到循环缓冲区中的内容多于覆盖传入数据速率中的最大时间抖动所需的数量。尝试等到循环缓冲区中有半秒的音频后再开始播放。然后试验填充量。

在 iOS 中播放原始 PCM 数据缓冲区时音频失真

Distorted audio when playing raw PCM data buffer in iOS

audio

audiounit

ios

opus

swift