Using VoiceProcessingIO for echo cancellation on macOS

XXXSpeakerDevice.m

OSStatus MyOutputRenderCallback(void* inRefCon, AudioUnitRenderActionFlags* ioActionFlags, const AudioTimeStamp* inTimeStamp, UInt32 inBusNumber, UInt32 inNumberFrames, AudioBufferList* ioData)
{
  // Not being called at all.
}

@implementation XXXSpeakerDevice
{
  AUGraph _graph;
}

- (void) dealloc
{
  [self stop];
}

#define HANDLE_STATUS(x) if(x) { NSLog(@"OSStatus: %d", x); return NO; }

- (BOOL) start
{
  OSStatus status = noErr;

  // * * *.

  // Graph initialization.
  status = NewAUGraph(&_graph);

  HANDLE_STATUS(status)

  // * * *.

  // Resampling node.
  AudioComponentDescription resamplingAudioComponentDescription = [self resamplingAudioComponentDescription];

  AUNode resamplingNode;

  status = AUGraphAddNode(_graph, &resamplingAudioComponentDescription, &resamplingNode);

  HANDLE_STATUS(status)

  // * * *.

  // Voice processing node.
  AudioComponentDescription voiceProcessingAudioComponentDescription = [self voiceProcessingAudioComponentDescription];

  AUNode voiceProcessingNode;

  status = AUGraphAddNode(_graph, &voiceProcessingAudioComponentDescription, &voiceProcessingNode);

  HANDLE_STATUS(status)

  // * * *.

  // (Resampling → voice processing) connection.
  status = AUGraphConnectNodeInput(_graph, resamplingNode, 0, voiceProcessingNode, 0);

  HANDLE_STATUS(status)

  // * * *.

  // Graph open.
  status = AUGraphOpen(_graph);

  HANDLE_STATUS(status)

  // * * *.

  // Resampling node input callback.
  AURenderCallbackStruct inputCallback;

  inputCallback.inputProc = MyOutputRenderCallback;

  inputCallback.inputProcRefCon = (__bridge void* _Nullable)(self);

  status = AUGraphSetNodeInputCallback(_graph, resamplingNode, 0, &inputCallback);

  HANDLE_STATUS(status)

  // * * *.

  // Get the underlying audio unit from the resampling node.
  AudioUnit resamplingAudioUnit;

  status = AUGraphNodeInfo(_graph, resamplingNode, NULL, &resamplingAudioUnit);

  HANDLE_STATUS(status)

  // * * *.

  // Get the underlying audio unit from the voice processing node.
  AudioUnit voiceProcessingAudioUnit;

  status = AUGraphNodeInfo(_graph, voiceProcessingNode, NULL, &voiceProcessingAudioUnit);

  HANDLE_STATUS(status)

  // * * *.

  // 0 stands for 'muting off'.
  const UInt32 value = 0;

  status = AudioUnitSetProperty(voiceProcessingAudioUnit, kAUVoiceIOProperty_MuteOutput, kAudioUnitScope_Global, 1, &value, sizeof(value));

  HANDLE_STATUS(status)

  // * * *.

  // Set resampling node's input stream format.
  AudioStreamBasicDescription streamFormat = [self myStreamFormat];

  status = AudioUnitSetProperty(resamplingAudioUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input, 0, &streamFormat, sizeof(streamFormat));

  HANDLE_STATUS(status)

  // * * *.

  {{
    AudioStreamBasicDescription streamFormat;

    UInt32 size = sizeof(streamFormat);

    AudioUnitGetProperty(voiceProcessingAudioUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input, 0, &streamFormat, &size);

    streamFormat.mChannelsPerFrame = 1;

    // Set resampling node's output stream format.
    status = AudioUnitSetProperty(resamplingAudioUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Output, 0, &streamFormat, size);

    HANDLE_STATUS(status)
  }}

  // * * *.

  // Graph update.
  status = AUGraphUpdate(_graph, NULL);

  HANDLE_STATUS(status)

  // * * *.

  status = AUGraphInitialize(_graph);

  HANDLE_STATUS(status)

  // * * *.

  status = AUGraphStart(_graph);

  HANDLE_STATUS(status)

  // * * *.

  CAShow(_graph);

  // * * *.

  return YES;
}

- (AudioComponentDescription) voiceProcessingAudioComponentDescription
{
  AudioComponentDescription outputComponentDescription;

  outputComponentDescription.componentType = kAudioUnitType_Output;

  outputComponentDescription.componentSubType = kAudioUnitSubType_VoiceProcessingIO;

  outputComponentDescription.componentManufacturer = kAudioUnitManufacturer_Apple;

  outputComponentDescription.componentFlags = 0;

  outputComponentDescription.componentFlagsMask = 0;

  return outputComponentDescription;
}

- (AudioComponentDescription) resamplingAudioComponentDescription
{
  AudioComponentDescription resamplingAudioComponentDescription;

  resamplingAudioComponentDescription.componentType = kAudioUnitType_FormatConverter;

  resamplingAudioComponentDescription.componentSubType = kAudioUnitSubType_AUConverter;

  resamplingAudioComponentDescription.componentManufacturer = kAudioUnitManufacturer_Apple;

  resamplingAudioComponentDescription.componentFlags = 0;

  resamplingAudioComponentDescription.componentFlagsMask = 0;

  return resamplingAudioComponentDescription;
}

- (AudioStreamBasicDescription) myStreamFormat
{
  AudioStreamBasicDescription streamFormat;

  UInt32 byteSize = sizeof(short);

  streamFormat.mFormatFlags = kAudioFormatFlagIsSignedInteger;
  
  streamFormat.mSampleRate = 48000;

  streamFormat.mFormatID = kAudioFormatLinearPCM;

  streamFormat.mBytesPerPacket = byteSize;

  streamFormat.mFramesPerPacket = 1;

  streamFormat.mBytesPerFrame = byteSize;

  streamFormat.mChannelsPerFrame = 1; // Mono.

  streamFormat.mBitsPerChannel = 8 * byteSize;

  return streamFormat;
}

#define HANDLE_STATUS_NORETURN(x) if(x) { NSLog(@"OSStatus: %d", x); }

- (void) stop
{
  if(_graph)
  {
    OSStatus status = noErr;

    // * * *.

    status = AUGraphStop(_graph);

    HANDLE_STATUS_NORETURN(status)

    // * * *.

    status = AUGraphUninitialize(_graph);

    HANDLE_STATUS_NORETURN(status)

    // * * *.

    status = AUGraphClose(_graph);

    HANDLE_STATUS_NORETURN(status)

    // * * *.

    status = DisposeAUGraph(_graph);

    HANDLE_STATUS_NORETURN(status)

    // * * *.

    _graph = NULL;
  }
}

I am developing an VOIP app on macOS. This code for echo cancellation works? Thanks