@interface AudioTapProcessor : NSObject

@property (nonatomic, strong) AVPlayerItem *item;
@property (nonatomic, strong) id<AudioProcessorDelegate> delegate;

- (instancetype)initWithDelegate:(id<AudioProcessorDelegate>)delegate
    item:(AVPlayerItem *)item;
- (void)startProcessing;
- (void)stopProcessing;

@end

void init(MTAudioProcessingTapRef tap, void *clientInfo, void
**tapStorageOut) {
    *tapStorageOut = clientInfo;
}

void finalize(MTAudioProcessingTapRef tap) {}

void prepare(
         MTAudioProcessingTapRef tap,
         CMItemCount maxFrames,
         const AudioStreamBasicDescription *processingFormat
         ) {}

void unprepare(MTAudioProcessingTapRef tap) {}

void process(
         MTAudioProcessingTapRef tap,
         CMItemCount numberFrames,
         MTAudioProcessingTapFlags flags,
         AudioBufferList *bufferListInOut,
         CMItemCount *numberFramesOut,
         MTAudioProcessingTapFlags *flagsOut
         ) {
 //Random crashes here if I declare the delegate weak
 //Something like AUDeferredRenderer-0x7ff8f448ef (364): EXC_BAD_ACCESS (code=EXC_I386_GPFLT)
  AudioTapProcessor *processor = (__bridge AudioTapProcessor *)MTAudioProcessingTapGetStorage(tap);

  OSStatus err = MTAudioProcessingTapGetSourceAudio(tap, numberFrames, bufferListInOut, flagsOut, NULL, numberFramesOut);

  AudioBuffer *pBuffer = &bufferListInOut->mBuffers[0];
  UInt32 frameLength = pBuffer->mDataByteSize / sizeof(float);
  float *pData = (float *)pBuffer->mData;

  if (err == noErr && processor) {
    if ([processor.delegate
      respondsToSelector:@selector(updateWith:withSize:)]) {
      [processor.delegate updateWith:pData withSize:frameLength];
    }
  }
 }

- (void)stopProcessing
{
  [self.item removeObserver:self forKeyPath:@"status"];
AVMutableAudioMixInputParameters *params =
(AVMutableAudioMixInputParameters *) _item.audioMix.inputParameters[0];
  MTAudioProcessingTapRef tap = params.audioTapProcessor;
  self.item.audioMix = nil;
  CFRelease(tap);
  //By doing this the tap processor does call its unprepare and finalize methods, so it is being deallocated fine.
}

var processor: AudioTapProcessor!

override func prepareForPlayback() {
  super.prepareForPlayback()
  if processor == nil {
    processor = AudioTapProcessor(delegate: self, item: item)
    processor.startProcessing()
  }
}

override func viewWillDisappear(_ animated: Bool) {
   super.viewWillDisappear(animated)
   player.pause()
}

deinit {
  //I tried to do this early in the lifecycle(viewWillDissapear) and it is the same thing.
   processor.stopProcessing()
}