将 AVAudioPCMBuffer 转换为 NSData 并返回

Question

如何将AVAudioPCMBuffer 转换为NSData？如果应该这样做

let data = NSData(bytes: buffer.floatChannelData, length: bufferLength)

那么如何计算bufferLength？

以及如何将NSData 转换为AVAudioPCMBuffer？

Answer 1

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。

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

func toPCMBuffer(data: NSData) -> AVAudioPCMBuffer? {
    let audioFormat = AVAudioFormat(commonFormat: .pcmFormatFloat32, sampleRate: 8000, channels: 1, interleaved: false)!  // given NSData audio format
    guard let PCMBuffer = AVAudioPCMBuffer(pcmFormat: audioFormat, frameCapacity: UInt32(data.length) / audioFormat.streamDescription.pointee.mBytesPerFrame) else {
        return nil
    }
    PCMBuffer.frameLength = PCMBuffer.frameCapacity
    let channels = UnsafeBufferPointer(start: PCMBuffer.floatChannelData, count: Int(PCMBuffer.format.channelCount))
    data.getBytes(UnsafeMutableRawPointer(channels[0]) , length: data.length)
    return PCMBuffer
}

Answer 2

如果您通过 audioBufferList API 进行复制，则复制缓冲区会容易得多。无论实际缓冲区的格式是什么，这也有效。

extension Data {
    init(buffer: AVAudioPCMBuffer, time: AVAudioTime) {
        let audioBuffer = buffer.audioBufferList.pointee.mBuffers
        self.init(bytes: audioBuffer.mData!, count: Int(audioBuffer.mDataByteSize))
    }

    func makePCMBuffer(format: AVAudioFormat) -> AVAudioPCMBuffer? {
        let streamDesc = format.streamDescription.pointee
        let frameCapacity = UInt32(count) / streamDesc.mBytesPerFrame
        guard let buffer = AVAudioPCMBuffer(pcmFormat: format, frameCapacity: frameCapacity) else { return nil }

        buffer.frameLength = buffer.frameCapacity
        let audioBuffer = buffer.audioBufferList.pointee.mBuffers

        withUnsafeBytes { (bufferPointer) in
            guard let addr = bufferPointer.baseAddress else { return }
            audioBuffer.mData?.copyMemory(from: addr, byteCount: Int(audioBuffer.mDataByteSize))
        }

        return buffer
    }
}