Passing audio to a C++ application

[geoffw64]

Hi Devin,
I am developing a digital signal processing application using BlackHole and Apple AudioToolbox. The idea is to pass audio from a player (Jriver Media Center and Quicktime) to my application through BlackHole
Environment:

• MacOS Sonoma 14.4.1

• Xcode 15.4

• Quicktime 10.5 and JRiver Media Center 32

• BlackHole 2ch and 16ch
  Problem: All audio samples received are zero.
  Steps to recreate:

• Set Mac Settings Sound audio output to BlackHole 2ch.

• Set Mac Settings Sound audio input to BlackHole 2ch.

• Authorise Xcode to access Microphone.

• In Audio MIDI set "Use this device for sound input" and "Use this device for sound output". Set volume of both to 1.0 .

• Play a 44.1 16-bit stereo FLAC file using Quicktime.

• Start C++ application - key details of my code below...

  AudioStreamBasicDescription asbd = { 0 };
  asbd.mFormatID = kAudioFormatLinearPCM;
  asbd.mFormatFlags = kLinearPCMFormatFlagIsFloat | kLinearPCMFormatFlagIsPacked;
  asbd.mSampleRate = 48000;
  asbd.mBitsPerChannel = 32;
  asbd.mBytesPerFrame = 8;
  asbd.mChannelsPerFrame = 2;
  asbd.mBytesPerPacket = asbd.mBytesPerFrame;
  asbd.mFramesPerPacket = 1;
  status = AudioQueueNewInput(&asbd,
  read_audio_callback,
  &userdata,
  NULL,
  NULL,
  0,
  &queue_ref);
  for (uint8_t b = 0; b < num_buffers; b++) {
  AudioQueueBufferRef buf_ref;
  status = AudioQueueAllocateBuffer(queue_ref, audio_buf_size, &buf_ref);
  printf("Allocate buffer status: %d length %d\n", status, buf_ref->mAudioDataByteSize);
  status = AudioQueueEnqueueBuffer (queue_ref, buf_ref, 0, NULL);
  printf ("Initial Enqueue Buffer status: %d\n", status);
  }
  status = AudioQueueStart(queue_ref, NULL);

Here is my callback:
void read_audio_callback(void * ptr, AudioQueueRef queue_ref, AudioQueueBufferRef buf_ref, const AudioTimeStamp * ts_not_used, uint32_t num_packets, const AudioStreamPacketDescription * aspd_not_used) {
if (num_packets > 0) {
uint32_t bytesize = buf_ref -> mAudioDataByteSize;
float * sample_buf_float = (float *)buf_ref -> mAudioData;
float data[bytesize / 4];
memcpy(data, sample_buf_float, bytesize);
OSStatus status = AudioQueueEnqueueBuffer(queue_ref, buf_ref, 0, NULL);
printf ("Enqueue buffer status: %d\n", status);
printf("Buffer length %d Packets received %d\n", bytesize, num_packets);
for (int j = 0; j < bytesize / 4; j++) {
printf("%f",data[j]);
}
}
printf("read_audio_callback called!\n");
}

All calls to Apple Audio functions return status of 0.

The samples in the buffer are all 0.0 . Why would this be the case?
Also, my callback is called even when playback is stopped. num_packets is always > 0 .

Appreciate any help.
Thanks in advance,
Geoff.

[geoffw64]

More info... I'm using a Mac Mini which does not have a built-in microphone.
However, Audio MIDi happily allows BlackHole to be Used for Sound Input in Audio MIDI.

Also, I get this message in the Xcode console when my app first starts: AddInstanceForFactory: No factory registered for id <CFUUID 0x600000970380> F8BB1C28-BAE8-11D6-9C31-00039315CD46 Google doesn't turn up anything suggesting this is causing the issue I'm seeing though. Seems to be related to Xcode.

[geoffw64]

To try another tack, I've downloaded and compiled the Apple sample recording program from here:
https://developer.apple.com/library/archive/samplecode/AudioQueueTools/Listings/aqrecord_cpp.html#//apple_ref/doc/uid/DTS10004380-aqrecord_cpp-DontLinkElementID_20
Here is what I did:
Played a flac file using Quicktime and ran the Apple recording application to record 30 seconds of music.
I used a multi-output device consisting of Black Hole 2ch and my AV processor so I could hear the audio while recording.
The recording (output file) contains all zero samples. Black Hole doesn't seem to be passing the audio samples through to the C++ recording program.
Then I tried using BlackHole 2ch as a stand-alone audio device. Same result.
Finally, I recorded using a .wav file as input. Same result.
I am certain the audio devices were set to a sensible volume level and not muted.

Here is one of the recordings (zipped):
recording.wav.zip

Here is the Xcode console output for one 30 second recording:
AddInstanceForFactory: No factory registered for id <CFUUID 0x600002e6c3a0> F8BB1C28-BAE8-11D6-9C31-00039315CD46
AQME.h:262 BlackHole2ch_UID (1): skipping output stream 0 0 0x0
Recording...
AQME.h:262 BlackHole2ch_UID (173): skipping output stream 0 0 0x0
AQME.h:262 BlackHole2ch_UID (173): skipping output stream 0 0 0x0
AQME.h:262 BlackHole2ch_UID (173): skipping output stream 0 0 0x0
AQME.h:262 BlackHole2ch_UID (173): skipping output stream 0 0 0x0
AQME.h:262 BlackHole2ch_UID (173): skipping output stream 0 0 0x0
AQME.h:262 BlackHole2ch_UID (173): skipping output stream 0 0 0x0
AQME.h:262 BlackHole2ch_UID (173): skipping output stream 0 0 0x0
AQME.h:262 BlackHole2ch_UID (173): skipping output stream 0 0 0x0
AQME.h:262 BlackHole2ch_UID (173): skipping output stream 0 0 0x0
AQME.h:262 BlackHole2ch_UID (173): skipping output stream 0 0 0x0
AQME.h:262 BlackHole2ch_UID (173): skipping output stream 0 0 0x0
AQME.h:262 BlackHole2ch_UID (173): skipping output stream 0 0 0x0
AQME.h:262 BlackHole2ch_UID (173): skipping output stream 0 0 0x0
AQME.h:262 BlackHole2ch_UID (173): skipping output stream 0 0 0x0

• recording done *
  Program ended with exit code: 0

Am I doing something wrong?
What further diagnosis can I do?

Keen to contribute to the Black Hole project if I can get it to work.

Thanks in advance,
Geoff.

[geoffw64]

Resolved.
I found a message relating to microphone entitlements in the console. Adding the entitlement to the project in Xcode resolved the issue.