如何在 Swift 中将 CMSampleBuffer 转换为数据？

Question

我需要将CMSampleBuffer 转换为Data 格式。我正在为音频相关任务使用一个第三方框架。该框架为我提供CMSampleBuffer 对象中的流式（即实时音频）音频。

像这样：

func didAudioStreaming(audioSample: CMSampleBuffer!) {
    //Here I need to conver this to Data format. 
    //Because I am using GRPC framework for Audio Recognization, 
}

请提供将CMSampleBuffer 转换为Data 的步骤。

仅供参考

    let formatDesc:CMFormatDescription? = CMSampleBufferGetFormatDescription(audioSample)

    <CMAudioFormatDescription 0x17010d890 [0x1b453ebb8]> {
    mediaType:'soun' 
    mediaSubType:'lpcm' 
    mediaSpecific: {
        ASBD: {
            mSampleRate: 16000.000000 
            mFormatID: 'lpcm' 
            mFormatFlags: 0xc 
            mBytesPerPacket: 2 
            mFramesPerPacket: 1 
            mBytesPerFrame: 2 
            mChannelsPerFrame: 1 
            mBitsPerChannel: 16     } 
        cookie: {(null)} 
        ACL: {(null)}
        FormatList Array: {(null)} 
    } 
    extensions: {(null)}
}

Answer 1

尝试下面的代码将 CMSampleBuffer 转换为 NSData。

let imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer)
CVPixelBufferLockBaseAddress(imageBuffer!, CVPixelBufferLockFlags(rawValue: 0))
let bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer!)
let height = CVPixelBufferGetHeight(imageBuffer!)
let src_buff = CVPixelBufferGetBaseAddress(imageBuffer!)
let data = NSData(bytes: src_buff, length: bytesPerRow * height)
CVPixelBufferUnlockBaseAddress(imageBuffer!, CVPixelBufferLockFlags(rawValue: 0))

编辑-

对于 AudioBuffer 使用下面的代码 -

var audioBufferList = AudioBufferList()
var data = Data()
var blockBuffer : CMBlockBuffer?

CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer(sampleBuffer, nil, &audioBufferList, MemoryLayout<AudioBufferList>.size, nil, nil, 0, &blockBuffer)

let buffers = UnsafeBufferPointer<AudioBuffer>(start: &audioBufferList.mBuffers, count: Int(audioBufferList.mNumberBuffers))

for audioBuffer in buffers {
    let frame = audioBuffer.mData?.assumingMemoryBound(to: UInt8.self)
    data.append(frame!, count: Int(audioBuffer.mDataByteSize))
}

Answer 2

使用CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer 需要在某个时间点调用CFRelease(blockBuffer)，因为缓冲区被保留，如果不释放，缓冲区池最终将变为空，并且不会生成新的CMSampleBuffer。

我建议使用以下方法直接获取数据：

CMBlockBufferRef blockBuffer = CMSampleBufferGetDataBuffer(sampleBuffer);
size_t lengthAtOffset;
size_t totalLength;
char *data;
CMBlockBufferGetDataPointer(blockBuffer, 0, &lengthAtOffset, &totalLength, &data);

NSData *audioData = [NSData dataWithBytes:data length:totalLength];