如何调用CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer？

Question

我试图弄清楚如何AVFoundation在Swift中调用此函数。我花了很多时间摆弄声明和语法，并且到此为止。编译器通常很高兴，但我还有最后一个难题。

public func captureOutput(
    captureOutput: AVCaptureOutput!,
    didOutputSampleBuffer sampleBuffer: CMSampleBuffer!,
    fromConnection connection: AVCaptureConnection!
) {
    let samplesInBuffer = CMSampleBufferGetNumSamples(sampleBuffer)
    var audioBufferList: AudioBufferList

    var buffer: Unmanaged<CMBlockBuffer>? = nil

    CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer(
        sampleBuffer,
        nil,
        &audioBufferList,
        UInt(sizeof(audioBufferList.dynamicType)),
        nil,
        nil,
        UInt32(kCMSampleBufferFlag_AudioBufferList_Assure16ByteAlignment),
        &buffer
    )

    // do stuff
}

编译器抱怨第三个和第四个参数：

变量'audioBufferList'的初始化之前获取的地址

和

初始化之前使用的变量“ audioBufferList”

那我应该在这里做什么？

我正在研究这个StackOverflow答案，但它是Objective-C。我正在尝试将其翻译成Swift，但是遇到了这个问题。

还是有更好的方法？我需要一次从缓冲区读取一个样本的数据，所以我基本上是在尝试获取可以迭代的样本数组。

Answer 1

免责声明：我刚刚尝试将代码从通过 AVAssetReader 读取音频样本转换为 Swift，并验证它是否可以编译。我没有测试过它是否真的有效。

// Needs to be initialized somehow, even if we take only the address
var audioBufferList = AudioBufferList(mNumberBuffers: 1,
      mBuffers: AudioBuffer(mNumberChannels: 0, mDataByteSize: 0, mData: nil))

var buffer: Unmanaged<CMBlockBuffer>? = nil

CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer(
    sampleBuffer,
    nil,
    &audioBufferList,
    UInt(sizeof(audioBufferList.dynamicType)),
    nil,
    nil,
    UInt32(kCMSampleBufferFlag_AudioBufferList_Assure16ByteAlignment),
    &buffer
)

// Ensure that the buffer is released automatically.
let buf = buffer!.takeRetainedValue() 

// Create UnsafeBufferPointer from the variable length array starting at audioBufferList.mBuffers
let audioBuffers = UnsafeBufferPointer<AudioBuffer>(start: &audioBufferList.mBuffers,
    count: Int(audioBufferList.mNumberBuffers))

for audioBuffer in audioBuffers {
    // Create UnsafeBufferPointer<Int16> from the buffer data pointer
    var samples = UnsafeMutableBufferPointer<Int16>(start: UnsafeMutablePointer(audioBuffer.mData),
        count: Int(audioBuffer.mDataByteSize)/sizeof(Int16))

    for sample in samples {
        // ....
    }
}