ios - swift 3 : Using AVCaptureAudioDataOutput to analyze audio input

Question

我正在尝试使用 AVCaptureAudioDataOutput 来分析音频输入，如 here 所述.这不是我自己想出来的东西，所以我正在复制这个例子，但我遇到了困难。

Swift 3 中的 Xcode 提示我进行了一些更改。我在分配 samples 行时遇到编译错误。 Xcode 说，“无法使用类型为‘(UnsafeMutableRawPointer?)’的参数列表为类型‘UnsafeMutablePointer<_> 调用初始化器”

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这段代码？

Answer 1

答案是我需要包装 buf.mData在OpaquePointer .即，在调用 UnsafeMutableBufferPointer<Int16>(OpaquePointer(buff.mData)) 时, 改变

start: UnsafeMutablePointer(buff.mData)

到

start: UnsafeMutablePointer(OpaquePointer(buff.mData))

这是完整的代码，针对 Swift 3 进行了更新:

    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)))" )
}

这满足了编译器的要求，并且似乎生成了合理的数字。