swift - 分解 Uint32 的数据字节缓冲区

Question

我正在使用 AVCaptureSession 捕获音频。在用于处理捕获的数据的回调函数中，我将流放在数据结构(字节缓冲区)中。看起来数据是 UInt8(对于字节缓冲区有意义)，但我相信流数据是 UInt32。

我不确定我应该执行以下哪些操作，但我无法让它们中的任何一个工作。我是否:

1. 将数据转换为 UInt32 而不是 UInt8？
2. 读取数据时，取 4 个字节组成 UInt32？
3. 将我的捕获 session 更改为 UInt8？
4. 放弃数据结构，自己做？

我的回调函数是:

    func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {

    var audioBufferList = AudioBufferList()
    var data = Data()
    var blockBuffer: CMBlockBuffer?

    // Put the sample buffer in to a list of audio buffers (audioBufferList)
    CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer(sampleBuffer, bufferListSizeNeededOut: nil, bufferListOut: &audioBufferList, bufferListSize: MemoryLayout<AudioBufferList>.size, blockBufferAllocator: nil, blockBufferMemoryAllocator: nil, flags: 0, blockBufferOut: &blockBuffer)
    // Extract the BufferList in to an array of buffers
    let buffers = UnsafeBufferPointer<AudioBuffer>(start: &audioBufferList.mBuffers, count: Int(audioBufferList.mNumberBuffers))
    // for each buffer, extract the frame.  There should only be one buffer as we are recording in mono!
    for audioBuffer in buffers {
        assert(audioBuffer.mNumberChannels == 1)        // it should always be 1 for mono channel
        let frame = audioBuffer.mData?.assumingMemoryBound(to: UInt8.self)
        data.append(frame!, count: Int(audioBuffer.mDataByteSize) / 8)
    }

    // limit how much of the sample we pass through.
    viewDelegate?.gotSoundData(data.prefix(MAX_POINTS))
}

所有的gotSoundData从view到多个子view去处理

func addSamples(samples: Data) {
    //if (isHidden) { return }

    samples.forEach { sample in
        [...process each byte...]
    }
}

我可以看到 Data.append 有定义:

mutating func append(_ bytes: UnsafePointer<UInt8>, count: Int)

Answer 1

Meggar 帮助我专注于选项 4 - 使用我自己的结构 [Int16]。如果有人对选项 1 感兴趣，请查看我后来发现的此链接，该链接扩展了 Data 以获取更多数据类型: round trip Swift number type to/from Data

回调函数:

    func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {
    var audioBufferList = AudioBufferList()
    var blockBuffer: CMBlockBuffer?

    // Put the sample buffer in to a list of audio buffers (audioBufferList)
    CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer(sampleBuffer, bufferListSizeNeededOut: nil, bufferListOut: &audioBufferList, bufferListSize: MemoryLayout<AudioBufferList>.size, blockBufferAllocator: nil, blockBufferMemoryAllocator: nil, flags: 0, blockBufferOut: &blockBuffer)
    // Extract the BufferList in to an array of buffers
    let audioBuffers = UnsafeBufferPointer<AudioBuffer>(start: &audioBufferList.mBuffers, count: Int(audioBufferList.mNumberBuffers))
    // For each buffer, extract the samples
    for audioBuffer in audioBuffers {
        let samplesCount = Int(audioBuffer.mDataByteSize) / MemoryLayout<Int16>.size
        let samplesPointer = audioBufferList.mBuffers.mData!.bindMemory(to: Int16.self, capacity: samplesCount)
        let samples = UnsafeMutableBufferPointer<Int16>(start: samplesPointer, count: samplesCount)
        //convert to a "safe" array for ease of use in delegate.
        var samplesArray:[Int16] = []
        for sample in samples {
            samplesArray.append(sample)
        }
        viewDelegate?.gotSample(samplesArray)
    }        
}

并且消费函数几乎保持不变:

func addSamples(samples: [Int16]) {
    samples.forEach { sample in
        [...process each Int16...]
    }
}