Swift 3：使用 AVCaptureAudioDataOutput 分析音频输入

我正在尝试使用 AVCaptureAudioDataOutput 来分析音频输入，如上所述here https://stackoverflow.com/questions/33030425/capturing-volume-levels-with-avcaptureaudiodataoutputsamplebufferdelegate-in-swi。这不是我自己能弄清楚的东西，所以我复制了这个例子，但我遇到了困难。

Swift 3 中的 Xcode 促使我做出了一些更改。我在分配行时遇到编译错误samples。 Xcode 说：“无法使用类型为‘(UnsafeMutableRawPointer?)’的参数列表调用类型‘UnsafeMutablePointer<_> 的初始化程序”

这是我修改后的代码：

func captureOutput(_ captureOutput: AVCaptureOutput!,
                    didOutputSampleBuffer sampleBuffer: CMSampleBuffer!,
                   from connection: AVCaptureConnection!){
    var buffer: CMBlockBuffer? = nil
    var audioBufferList = AudioBufferList(mNumberBuffers: 1,
                                          mBuffers: AudioBuffer(mNumberChannels: 1, mDataByteSize: 0, mData: nil))
    CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer(
        sampleBuffer,
        nil,
        &audioBufferList,
        MemoryLayout<AudioBufferList>.size,     // changed for Swift 3
        nil,
        nil,
        UInt32(kCMSampleBufferFlag_AudioBufferList_Assure16ByteAlignment),
        &buffer
    )
    let abl = UnsafeMutableAudioBufferListPointer(&audioBufferList)
    var sum:Int64 = 0
    var count:Int = 0
    var bufs:Int = 0
    for buf in abl {
        let samples = UnsafeMutableBufferPointer<Int16>(start: UnsafeMutablePointer(buf.mData),  // Error here
                                                        count: Int(buf.mDataByteSize)/sizeof(Int16))
        for sample in samples {
            let s = Int64(sample)
            sum = (sum + s*s)
            count += 1
        }
        bufs += 1
    }
    print( "found \(count) samples in \(bufs) buffers, sum is \(sum)" )
}

谁能告诉我如何修复此代码？

答案是我需要包装buf.mData in an OpaquePointer。即，在调用中UnsafeMutableBufferPointer<Int16>(OpaquePointer(buff.mData)), change

start: UnsafeMutablePointer(buff.mData)

to

start: UnsafeMutablePointer(OpaquePointer(buff.mData))

以下是针对 Swift 3 进行更新的完整代码：

    func captureOutput(_ captureOutput: AVCaptureOutput!,
                   didOutputSampleBuffer sampleBuffer: CMSampleBuffer!,
                   from connection: AVCaptureConnection!){
    var buffer: CMBlockBuffer? = nil
    var audioBufferList = AudioBufferList(mNumberBuffers: 1,
                                          mBuffers: AudioBuffer(mNumberChannels: 1, mDataByteSize: 0, mData: nil))
    CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer(
        sampleBuffer,
        nil,
        &audioBufferList,
        MemoryLayout<AudioBufferList>.size,
        nil,
        nil,
        UInt32(kCMSampleBufferFlag_AudioBufferList_Assure16ByteAlignment),
        &buffer
    )
    let abl = UnsafeMutableAudioBufferListPointer(&audioBufferList)
    var sum:Int64 = 0
    var count:Int = 0
    var bufs:Int = 0
    for buff in abl {
        let samples = UnsafeMutableBufferPointer<Int16>(start: UnsafeMutablePointer(OpaquePointer(buff.mData)),
                                                        count: Int(buff.mDataByteSize)/MemoryLayout<Int16>.size)
        for sample in samples {
            let s = Int64(sample)
            sum = (sum + s*s)
            count += 1
        }
        bufs += 1
    }
    print( "found \(count) samples in \(bufs) buffers, RMS is \(sqrt(Float(sum)/Float(count)))" )
}

这使编译器满意，并且似乎生成了合理的数字。