How to add a callback to AVAssetReader copyNextSampleBuffer?

Question

I am trying to read audio frames and decode them with AVAssetReader. I want to be able to read the frames asynchronously and add some kind of callback when a sample buffer was read. So after calling:

...
[reader startReading];
CMSampleBufferRef sample = [readerOutput copyNextSampleBuffer];

I want to be able to refer to and process this sample from my callback. Is that possible? If not, can you suggest how I can do it using maybe other classes from AVFoundation/Core Audio?

Answer 1

-(CMSampleBufferRef)[AVAssetReaderOutput copyNextSampleBuffer] is synchronous and I don't see any alternatives.

You can give it an asynchronous interface by doing something like this:

dispatch_async(myDecodingDispatchQueue, ^{
  CMSampleBufferRef sampleBuffer;
  while ((sampleBuffer = [readerOutput copyNextSampleBuffer])) {
    dispatch_async(myDispatchQueue, ^{
       [myCallbackObject myCallbackWithSampleBuffer:sampleBuffer];
    });
  }
  // examine AVAssetReader.status here to see reason for stopping
}