CoreAudio Playground #coreaudio #multichannel_audio

makefile

CXX = g++
CFLAGS=-Wall -std=c++14
LIBRARIES = -framework AudioUnit -framework CoreAudio

all:
	$(CC) $(CFLAGS) $(LIBRARIES) PreferredChannelLayout.cpp -o PreferredChannelLayout

clean:
	rm PreferredChannelLayout

PreferredChannelLayout.cpp

#include <iostream>
#include <cassert>

#include <AudioUnit/AudioUnit.h>
#include <CoreAudio/CoreAudio.h>

#define AU_OUT_BUS    0
#define AU_IN_BUS     1

#define DEBUG true // Set true to log the debugging messages.
#define LOG(...) DEBUG && fprintf(stdout, __VA_ARGS__)

OSStatus
get_preferred_channel_layout()
{
  AudioUnit outputUnit;
  AudioComponentDescription desc;
  AudioComponent comp;

  AudioDeviceID deviceId = 0;

  UInt32 size;
  OSStatus rv = noErr;
  Boolean writable;

  desc.componentType = kAudioUnitType_Output;
  // desc.componentSubType = kAudioUnitSubType_DefaultOutput;
  desc.componentSubType = kAudioUnitSubType_HALOutput;
  desc.componentManufacturer = kAudioUnitManufacturer_Apple;
  desc.componentFlags = 0;
  desc.componentFlagsMask = 0;

  comp = AudioComponentFindNext(NULL, &desc);
  if (comp == NULL) {
    LOG("%d: Could not find default audio output hardware.", rv);
    return rv;
  }

  rv = AudioComponentInstanceNew(comp, &outputUnit);
  if (rv != noErr) {
    LOG("%d: Could not link default audio output hardware to the audio unit.", rv);
    return rv;
  }

  // Check if we have IO
  UInt32 hasIO = 0;
  size = sizeof(hasIO);
  rv = AudioUnitGetProperty(outputUnit,
                            kAudioOutputUnitProperty_HasIO,
                            kAudioUnitScope_Output,
                            AU_OUT_BUS,
                            &hasIO,
                            &size);
  if (!hasIO) {
    LOG("%d: No audio output for this audio unit.", rv);
    return rv;
  }

  // Get the current device
  size = sizeof(deviceId);
  rv = AudioUnitGetProperty(outputUnit,
                            kAudioOutputUnitProperty_CurrentDevice,
                            kAudioUnitScope_Output,
                            AU_OUT_BUS,
                            &deviceId,
                            &size);
  if (rv != noErr) {
    LOG("%d: Could not get current audio output device.", rv);
    return rv;
  }
  LOG("device id: %d\n", deviceId);

  // Get the default channel layout
  size = 0;
  rv = AudioUnitGetPropertyInfo(outputUnit,
                                kAudioDevicePropertyPreferredChannelLayout,
                                kAudioUnitScope_Output,
                                AU_OUT_BUS,
                                &size,
                                &writable);
  if (rv != noErr) {
    LOG("%d: Could not get size of kAudioDevicePropertyPreferredChannelLayout.", rv);
    return rv;
  }
  assert(size > 0 && writable);

  AudioChannelLayout output_hw_layout;
  rv = AudioUnitGetProperty(outputUnit,
                            kAudioDevicePropertyPreferredChannelLayout,
                            kAudioUnitScope_Output,
                            AU_OUT_BUS,
                            &output_hw_layout,
                            &size);
  if (rv != noErr) {
    LOG("%d: Could not get kAudioDevicePropertyPreferredChannelLayout.", rv);
    return rv;
  }

  if (output_hw_layout.mChannelLayoutTag != kAudioChannelLayoutTag_UseChannelDescriptions) {
    // kAudioChannelLayoutTag_UseChannelBitmap
    // kAudioChannelLayoutTag_Mono
    // kAudioChannelLayoutTag_Stereo
    // ....
    LOG("%d: We only handle UseChannelDescriptions for now.", rv);
    return rv;
  }

  LOG("channel layout:\n");
  for (UInt32 i = 0; i < output_hw_layout.mNumberChannelDescriptions; ++i) {
    LOG("[%d] %d(0x%x)\n", i, output_hw_layout.mChannelDescriptions[i].mChannelLabel, output_hw_layout.mChannelDescriptions[i].mChannelLabel);
  }

  return rv;
}

int main()
{
  get_preferred_channel_layout();
  return 0;
}