Deep Copy of Audio CMSampleBuffer

Question

I am trying to create a copy of a CMSampleBuffer as returned by captureOutput in a AVCaptureAudioDataOutputSampleBufferDelegate.

The problem I am having

Answer 1

Here is a working solution I finally implemented. I sent this snippet to Apple Developer Technical support and asked them to check if it is a correct way to copy incoming sample buffer. The basic idea is copy AudioBufferList and then create a CMSampleBuffer and set AudioBufferList to this 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;
}

Code-Level Support answer:

This code looks ok (though you’ll want to add some additional error checking). I've successfully tested it in an app that implements the AVCaptureAudioDataOutput delegate captureOutput:didOutputSampleBuffer:fromConnection: method to capture and record audio. The captured audio I'm getting when using this deep copy code appears to be the same as what I get when directly using the provided sample buffer (without the deep copy).

Apple Developer Technical Support