iOS，通过 AudioUnit 从 48K 到 16K 的音频重采样

如何解决iOS，通过 AudioUnit 从 48K 到 16K 的音频重采样

我一直在尝试使用 AudioUnit 或 AudioConverterRef 将我的实时 PCM 单声道、48000 采样率重新采样到 16000 采样率单声道，但我在两者上都没有成功其中。

我查看了以下资源，但没有发现它们有多大帮助。

• https://developer.apple.com/forums/thread/70694
• iOS: How to resample audio(PCM data) using Audio Unit at runtime?
• iOS convert audio sample rate from 16 kHz to 8 kHz

我使用 AudioConverterRef 的代码是

     var inputFormat = CAStreamBasicDescription(
        sampleRate: Double(Constants.SAMPLE_RATE),numChannels: 1,pcmf: .int16,isInterleaved: false
    )
    
    var outputFormat = CAStreamBasicDescription(
        sampleRate: Double(16000),isInterleaved: false
    )
    
    status = AudioConverterNew(
            &inputFormat!,&outputFormat!,&converter48To16
    )
    
    if status != noErr {
        print("ERROR HERE: \(status)")
    }
    
    
    let outputBytes = outputFormat!.mBytesPerPacket * (640 * 1280 / inputFormat!.mBytesPerPacket)
    
    let outputBuffer = UnsafeMutablePointer<CChar>.allocate(capacity: Int(outputBytes))
    
    defer { outputBuffer.deallocate() }
    
    var outputBufferList = audiobufferlist()
    outputBufferList.mNumberBuffers = 1
    outputBufferList.mBuffers.mNumberChannels = 1
    outputBufferList.mBuffers.mDataByteSize = outputBytes
    outputBufferList.mBuffers.mData = UnsafeMutableRawPointer(outputBuffer)
    

    var outputDataPacketSize = outputBytes / outputFormat!.mBytesPerPacket
    
     status = AudioConverterFillComplexBuffer(
        converter48To16!,conversionAudioController_Callback,UnsafeMutableRawPointer(Unmanaged.passUnretained(self).toOpaque()),&outputDataPacketSize,&outputBufferList,nil
    )
    
    if status != noErr {
        print("ERROR HERE: \(status)")
    }

并且回调是

let conversionAudioController_Callback: AudioConverterComplexInputDataProc = {(
inAudioConverter,ioNumberDataPackets,ioData,outDataPacketDescription,inUserData) -> Osstatus in

let delegate = unsafeBitCast(inAudioConverter,to: AudioUnitDataChannelCallbackDelegate.self)

let result = delegate.performConversion(
    ioNumberDataPackets: ioNumberDataPackets,ioData: ioData,outDataPacketDescription: outDataPacketDescription,inUserData: inUserData
)

return noErr
}

我在这一行收到的错误是：

let delegate = unsafeBitCast(inAudioConverter,to: AudioUnitDataChannelCallbackDelegate.self)

线程 1：EXC_BAD_ACCESS（代码=1，地址=0xdbd000）

我在设置属性时没有遇到任何问题，但仅在实际执行代码时收到错误。

我目前正在以 48000 采样率录制 PCM 16 位单声道并尝试将其下采样到 16000

问题已更新：

 func performConversion(ioNumberDataPackets: UnsafeMutablePointer<UInt32>,ioData: UnsafeMutablePointer<audiobufferlist>,outDataPacketDescription: UnsafeMutablePointer<UnsafeMutablePointer<AudioStreamPacketDescription>?>?,inUserData: UnsafeMutableRawPointer?) -> Osstatus {
    
    let retained = inUserData!.assumingMemoryBound(to: audiobufferlist.self)

    let maxPackets = retained.pointee.mBuffers.mDataByteSize / 2
    if ioNumberDataPackets.pointee > maxPackets {
        ioNumberDataPackets.pointee = maxPackets
    }

    print("CONVERSION RUNNING...")

    let ioDataPtr = UnsafeMutableaudiobufferlistPointer(ioData)
    ioDataPtr[0].mData = UnsafeMutableRawPointer(inputBufferList?.mBuffers.mData)
    ioDataPtr[0].mDataByteSize = 1280
    ioDataPtr[0].mNumberChannels = inputBufferList!.mBuffers.mNumberChannels

    print("ioDataPtr: \(ioDataPtr[0].mDataByteSize)")
    return noErr
}

**************问题已编辑：************

记录数据和下采样 48K 到 16K。

 func performRecording(_ ioActionFlags: UnsafeMutablePointer<AudioUnitRenderActionFlags>,inTimeStamp: UnsafePointer<AudioTimeStamp>,inBufNumber: UInt32,inNumberFrames: UInt32,ioData: UnsafeMutablePointer<audiobufferlist>) -> Osstatus {
    
    print("*******************")
    var err: Osstatus = noErr
    
    err = AudioUnitRender(audioUnit!,ioActionFlags,inTimeStamp,1,inNumberFrames,ioData)
    
    var monoSamples = [Int16]()
    
    let rawAudioPointer = ioData[0].mBuffers.mData?.bindMemory(to: Int16.self,capacity: Int(inNumberFrames))
    if rawAudioPointer == nil {
        return noErr
    }
    monoSamples.append(contentsOf: UnsafeBufferPointer(start: rawAudioPointer,count: Int(inNumberFrames)))
    
    inputBufferList = ioData.pointee
    
    let outputBuffer = UnsafeMutablePointer<CChar>.allocate(capacity: 684)
    defer { outputBuffer.deallocate() }
    
    var fillBufferList = audiobufferlist()
    fillBufferList.mNumberBuffers = 1
    fillBufferList.mBuffers.mNumberChannels = 1
    fillBufferList.mBuffers.mDataByteSize = 684
    fillBufferList.mBuffers.mData = UnsafeMutableRawPointer(outputBuffer)

    var ioOutputDataPackets: UInt32 = 384

    inputBufferList = ioData.pointee

    let status = AudioConverterFillComplexBuffer(
        converter48To16!,&ioOutputDataPackets,&fillBufferList,nil
    )

    if status != noErr {
        print("ERROR HERE CONVERSION: \(status)")
    }
    
    print("MONOSAMPLE DATA \(monoSamples.count) and \(ioOutputDataPackets) and \(fillBufferList.mBuffers.mDataByteSize)")
    
    return err
}

录制没有问题，但是当我的输出与 mDataByteSize = 684 不匹配时，我收到 ERROR HERE CONVERSION: 1768846202

的错误