缓冲区长度为frameCapacity * bytesPerFrame。以下是可以在NSData和AVAudioPCMBuffer之间进行转换的函数。

func toNSData(PCMBuffer: AVAudioPCMBuffer) -> NSData {
    let channelCount = 1  // given PCMBuffer channel count is 1
    var channels = UnsafeBufferPointer(start: PCMBuffer.floatChannelData, count: channelCount)
    var ch0Data = NSData(bytes: channels[0], length:Int(PCMBuffer.frameCapacity * PCMBuffer.format.streamDescription.memory.mBytesPerFrame))
    return ch0Data
}

func toPCMBuffer(data: NSData) -> AVAudioPCMBuffer {
    let audioFormat = AVAudioFormat(commonFormat: AVAudioCommonFormat.PCMFormatFloat32, sampleRate: 8000, channels: 1, interleaved: false)  // given NSData audio format
    var PCMBuffer = AVAudioPCMBuffer(PCMFormat: audioFormat, frameCapacity: UInt32(data.length) / audioFormat.streamDescription.memory.mBytesPerFrame)
    PCMBuffer.frameLength = PCMBuffer.frameCapacity
    let channels = UnsafeBufferPointer(start: PCMBuffer.floatChannelData, count: Int(PCMBuffer.format.channelCount))
    data.getBytes(UnsafeMutablePointer<Void>(channels[0]) , length: data.length)
    return PCMBuffer
}