Audio CMSampleBuffer 的深拷贝

Question

我正在尝试在AVCaptureAudioDataOutputSampleBufferDelegate中创建由 captureOutput 返回的 CMSampleBuffer 的副本。

我遇到的问题是我的帧来自委托方法captureOutput:didOutputSampleBuffer:fromConnection:在我将它们保留在CFArray中很长时间后被丢弃。

显然，我需要创建传入缓冲区的深层副本以进行进一步处理。 我也知道CMSampleBufferCreateCopy只创建浅拷贝。

在 SO 上提出的相关问题很少：

• 从 CMSampleBuffer 中提取数据以创建深层副本
• 在 Swift 中创建 CMSampleBuffer 的副本返回 OSStatus -12743（无效的媒体格式）
• CMImageBuffer 或 CVImageBuffer 的深拷贝

但是它们都不能帮助我正确使用具有 12 个参数的CMSampleBufferCreate函数：

  CMSampleBufferRef copyBuffer;

  CMBlockBufferRef data = CMSampleBufferGetDataBuffer(sampleBuffer);
  CMFormatDescriptionRef formatDescription = CMSampleBufferGetFormatDescription(sampleBuffer);
  CMItemCount itemCount = CMSampleBufferGetNumSamples(sampleBuffer);

  CMTime duration = CMSampleBufferGetDuration(sampleBuffer);
  CMTime presentationStamp = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);
  CMSampleTimingInfo timingInfo;
  timingInfo.duration = duration;
  timingInfo.presentationTimeStamp = presentationStamp;
  timingInfo.decodeTimeStamp = CMSampleBufferGetDecodeTimeStamp(sampleBuffer);


  size_t sampleSize = CMBlockBufferGetDataLength(data);
  CMBlockBufferRef sampleData;

  if (CMBlockBufferCopyDataBytes(data, 0, sampleSize, &sampleData) != kCMBlockBufferNoErr) {
    VLog(@"error during copying sample buffer");
  }

  // Here I tried data and sampleData CMBlockBuffer instance, but no success
  OSStatus status = CMSampleBufferCreate(kCFAllocatorDefault, data, isDataReady, nil, nil, formatDescription, itemCount, 1, &timingInfo, 1, &sampleSize, &copyBuffer);

  if (!self.sampleBufferArray)  {
    self.sampleBufferArray = CFArrayCreateMutable(NULL, 0, &kCFTypeArrayCallBacks);
    //EXC_BAD_ACCESS crash when trying to add sampleBuffer to the array
    CFArrayAppendValue(self.sampleBufferArray, copyBuffer);
  } else  {
    CFArrayAppendValue(self.sampleBufferArray, copyBuffer);
  }

你如何深拷贝音频 CMSampleBuffer？ 随意在您的答案中使用任何语言（swift/objective-c）。

Answer 1

这是我最终实施的工作解决方案。 我将此片段发送给 Apple 开发人员技术支持，并要求他们检查复制传入样本缓冲区的方法是否正确。 基本思想是复制AudioBufferList ，然后创建一个CMSampleBuffer ，并将AudioBufferList设置为这个sample。

AudioBufferList audioBufferList;
CMBlockBufferRef blockBuffer;
//Create an AudioBufferList containing the data from the CMSampleBuffer,
//and a CMBlockBuffer which references the data in that AudioBufferList.
CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer(sampleBuffer, NULL, &audioBufferList, sizeof(audioBufferList), NULL, NULL, 0, &blockBuffer);
NSUInteger size = sizeof(audioBufferList);
char buffer[size];

memcpy(buffer, &audioBufferList, size);
//This is the Audio data.
NSData *bufferData = [NSData dataWithBytes:buffer length:size];

const void *copyBufferData = [bufferData bytes];
copyBufferData = (char *)copyBufferData;

CMSampleBufferRef copyBuffer = NULL;
OSStatus status = -1;

/* Format Description */

AudioStreamBasicDescription audioFormat = *CMAudioFormatDescriptionGetStreamBasicDescription((CMAudioFormatDescriptionRef) CMSampleBufferGetFormatDescription(sampleBuffer));

CMFormatDescriptionRef format = NULL;
status = CMAudioFormatDescriptionCreate(kCFAllocatorDefault, &audioFormat, 0, nil, 0, nil, nil, &format);

CMFormatDescriptionRef formatdes = NULL;
status = CMFormatDescriptionCreate(NULL, kCMMediaType_Audio, 'lpcm', NULL, &formatdes);
if (status != noErr)
{
  NSLog(@"Error in CMAudioFormatDescriptionCreator");
  CFRelease(blockBuffer);
  return;
}

/* Create sample Buffer */
CMItemCount framesCount = CMSampleBufferGetNumSamples(sampleBuffer);
CMSampleTimingInfo timing   = {.duration= CMTimeMake(1, 44100), .presentationTimeStamp= CMSampleBufferGetPresentationTimeStamp(sampleBuffer), .decodeTimeStamp= CMSampleBufferGetDecodeTimeStamp(sampleBuffer)};

status = CMSampleBufferCreate(kCFAllocatorDefault, nil , NO,nil,nil,format, framesCount, 1, &timing, 0, nil, &copyBuffer);

if( status != noErr) {
  NSLog(@"Error in CMSampleBufferCreate");
  CFRelease(blockBuffer);
  return;
}

/* Copy BufferList to Sample Buffer */
AudioBufferList receivedAudioBufferList;
memcpy(&receivedAudioBufferList, copyBufferData, sizeof(receivedAudioBufferList));

//Creates a CMBlockBuffer containing a copy of the data from the
//AudioBufferList.
status = CMSampleBufferSetDataBufferFromAudioBufferList(copyBuffer, kCFAllocatorDefault , kCFAllocatorDefault, 0, &receivedAudioBufferList);
if (status != noErr) {
  NSLog(@"Error in CMSampleBufferSetDataBufferFromAudioBufferList");
  CFRelease(blockBuffer);
  return;
}

代码级支持答案：

这段代码看起来不错（尽管您需要添加一些额外的错误检查）。 我已经在一个应用程序中成功地测试了它，该应用程序实现了 AVCaptureAudioDataOutput 委托captureOutput:didOutputSampleBuffer:fromConnection:捕获和录制音频的方法。 使用此深度复制代码时获得的捕获音频似乎与直接使用提供的样本缓冲区（没有深度复制）时获得的音频相同。

苹果开发者技术支持

Answer 2

在 Swift 中找不到合适的答案。 这是一个扩展：

extension CMSampleBuffer {
    func deepCopy() -> CMSampleBuffer? {
        guard let formatDesc = CMSampleBufferGetFormatDescription(self),
              let data = self.data else {
                  return nil
              }
        let nFrames = CMSampleBufferGetNumSamples(self)
        let pts = CMSampleBufferGetPresentationTimeStamp(self)
        let dataBuffer = data.withUnsafeBytes { (buffer) -> CMBlockBuffer? in
            var blockBuffer: CMBlockBuffer?
            let length: Int = data.count
            guard CMBlockBufferCreateWithMemoryBlock(
                allocator: kCFAllocatorDefault,
                memoryBlock: nil,
                blockLength: length,
                blockAllocator: nil,
                customBlockSource: nil,
                offsetToData: 0,
                dataLength: length,
                flags: 0,
                blockBufferOut: &blockBuffer) == noErr else {
                    print("Failed to create block")
                    return nil
                }
            guard CMBlockBufferReplaceDataBytes(
                with: buffer.baseAddress!,
                blockBuffer: blockBuffer!,
                offsetIntoDestination: 0,
                dataLength: length) == noErr else {
                    print("Failed to move bytes for block")
                    return nil
                }
            return blockBuffer
        }
        guard let dataBuffer = dataBuffer else {
            return nil
        }
        var newSampleBuffer: CMSampleBuffer?
        CMAudioSampleBufferCreateReadyWithPacketDescriptions(
            allocator: kCFAllocatorDefault,
            dataBuffer: dataBuffer,
            formatDescription: formatDesc,
            sampleCount: nFrames,
            presentationTimeStamp: pts,
            packetDescriptions: nil,
            sampleBufferOut: &newSampleBuffer
        )
        return newSampleBuffer
    }
}

Answer 3

LLooggaann 的解决方案更简单并且效果很好，但是，如果有人感兴趣，我将原始解决方案迁移到 Swift 5.6：

extension CMSampleBuffer {
    func deepCopy() -> CMSampleBuffer? {
        var audioBufferList : AudioBufferList = AudioBufferList()
        var blockBuffer : CMBlockBuffer?

        let sizeOfAudioBufferList = MemoryLayout<AudioBufferList>.size
        
        //Create an AudioBufferList containing the data from the CMSampleBuffer.
        CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer(self,
                                                                bufferListSizeNeededOut: nil,
                                                                bufferListOut: &audioBufferList,
                                                                bufferListSize: sizeOfAudioBufferList,
                                                                blockBufferAllocator: nil,
                                                                blockBufferMemoryAllocator: nil,
                                                                flags: 0,
                                                                blockBufferOut: &blockBuffer)

        guard audioBufferList.mNumberBuffers == 1 else { return nil }  //TODO: Make this generic for any number of buffers
        
        /* Deep copy the audio buffer */
        let audioBufferDataSize = Int(audioBufferList.mBuffers.mDataByteSize)
        let audioBuffer = audioBufferList.mBuffers
        let audioBufferDataCopyPointer = UnsafeMutableRawPointer.allocate(byteCount: audioBufferDataSize, alignment: 1)
                
        defer {
            audioBufferDataCopyPointer.deallocate()
        }
        
        memcpy(audioBufferDataCopyPointer, audioBufferList.mBuffers.mData, audioBufferDataSize)
        
        let copiedAudioBuffer = AudioBuffer(mNumberChannels: audioBuffer.mNumberChannels,
                                            mDataByteSize: audioBufferList.mBuffers.mDataByteSize,
                                            mData: audioBufferDataCopyPointer)
        
        /* Create a new audio buffer list with the deep copied audio buffer */
        var copiedAudioBufferList = AudioBufferList(mNumberBuffers: 1, mBuffers: copiedAudioBuffer)

        /* Copy audio format description, to be used in the new sample buffer */
        guard let sampleBufferFormatDescription = CMSampleBufferGetFormatDescription(self) else { return nil }

        /* Create copy of timing for new sample buffer */
        var duration = CMSampleBufferGetDuration(self)
        duration.value /= Int64(numSamples)
        var timing = CMSampleTimingInfo(duration: duration,
                                        presentationTimeStamp: CMSampleBufferGetPresentationTimeStamp(self),
                                        decodeTimeStamp: CMSampleBufferGetDecodeTimeStamp(self))

        /* New sample buffer preparation, using the audio format description, and the timing information. */
        let sampleCount = CMSampleBufferGetNumSamples(self)
        var newSampleBuffer : CMSampleBuffer?

        guard CMSampleBufferCreate(allocator: kCFAllocatorDefault,
                                   dataBuffer: nil,
                                   dataReady: false,
                                   makeDataReadyCallback: nil,
                                   refcon: nil,
                                   formatDescription: sampleBufferFormatDescription,
                                   sampleCount: sampleCount,
                                   sampleTimingEntryCount: 1,
                                   sampleTimingArray: &timing,
                                   sampleSizeEntryCount: 0,
                                   sampleSizeArray: nil,
                                   sampleBufferOut: &newSampleBuffer) == noErr else { return nil }

        //Create a CMBlockBuffer containing a copy of the data from the AudioBufferList, add to new sample buffer.
        let status = CMSampleBufferSetDataBufferFromAudioBufferList(newSampleBuffer!,
                                                                    blockBufferAllocator: kCFAllocatorDefault,
                                                                    blockBufferMemoryAllocator: kCFAllocatorDefault,
                                                                    flags: 0,
                                                                    bufferList: &copiedAudioBufferList)
        
        guard status == noErr else { return nil }

        return newSampleBuffer
    }
}