ios - 将 CMSampleBuffer 转换为 AVAudioPCMBuffer 以获取实时音频

Question

我正在尝试从 AVCaptureAudioDataOutputSampleBufferDelegate 的 captureOutput 返回的 CMSampleBuffer 中读取频率值。

我的想法是创建一个AVAudioPCMBuffer，这样我就可以读取它的floatChannelData。但我不确定如何将缓冲区传递给它。

我想我可以创建它:

public func captureOutput(_ output: AVCaptureOutput,
                              didOutput sampleBuffer: CMSampleBuffer,
                              from connection: AVCaptureConnection) {
guard let blockBuffer = CMSampleBufferGetDataBuffer(sampleBuffer) else {
  return
}
let length = CMBlockBufferGetDataLength(blockBuffer)

let audioFormat = AVAudioFormat(commonFormat: .pcmFormatFloat32, sampleRate: 44100, channels: 1, interleaved: false)
let pcmBuffer = AVAudioPCMBuffer(pcmFormat: audioFormat!, frameCapacity: AVAudioFrameCount(length))
pcmBuffer?.frameLength = pcmBuffer!.frameCapacity

但是我该如何填充它的数据呢？

Answer 1

这些方面的内容应该有所帮助:

var asbd = CMSampleBufferGetFormatDescription(sampleBuffer)!.audioStreamBasicDescription!
var audioBufferList = AudioBufferList()
var blockBuffer : CMBlockBuffer?

CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer(
    sampleBuffer,
    bufferListSizeNeededOut: nil,
    bufferListOut: &audioBufferList,
    bufferListSize: MemoryLayout<AudioBufferList>.size,
    blockBufferAllocator: nil,
    blockBufferMemoryAllocator: nil,
    flags: 0,
    blockBufferOut: &blockBuffer
)

let mBuffers = audioBufferList.mBuffers
let frameLength = AVAudioFrameCount(Int(mBuffers.mDataByteSize) / MemoryLayout<Float>.size)
let pcmBuffer = AVAudioPCMBuffer(pcmFormat: AVAudioFormat(streamDescription: &asbd)!, frameCapacity: frameLength)!
pcmBuffer.frameLength = frameLength
pcmBuffer.mutableAudioBufferList.pointee.mBuffers = mBuffers
pcmBuffer.mutableAudioBufferList.pointee.mNumberBuffers = 1

这似乎在捕获 session 的末尾创建了一个有效的 AVAudioPCMBuffer。但它现在的帧长度对于我的用例来说是错误的，所以需要做一些进一步的缓冲。