AudioToolbox.m

// Step 1: Register callback
    // Callback function will fill buffer. Then add to buffer queue.
    status = AudioQueueNewOutput(
                        &dataFormat,
                        BufferCallback,
                        (__bridge void * _Nullable)(self),
                        CFRunLoopGetCurrent(), // nil
                        kCFRunLoopCommonModes, // nil
                        0,
                        &_queue
                        );
    if (status != noErr) NSLog(@"AudioQueueNewOutput bitrate failed %d", status);