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 <cassert>
#include <iostream>

#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_number_of_supported_channels()
// {
//   AudioUnit au = nullptr;
//   AudioComponentDescription desc;
//   AudioComponent comp;
//
//   UInt32 size = 0;
//   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.\n", rv);
//     return rv;
//   }
//
//   rv = AudioComponentInstanceNew(comp, &au);
//   if (rv != noErr) {
//     LOG("%d: Could not link default audio output hardware to the audio unit.\n", rv);
//     return rv;
//   }
//
//   rv = AudioUnitGetPropertyInfo(au,
//                                 kAudioUnitProperty_SupportedNumChannels,
//                                 kAudioUnitScope_Global,
//                                 AU_OUT_BUS,
//                                 &size,
//                                 &writable);
//   if (rv != noErr) {
//     LOG("%d: Could not get size of kAudioUnitProperty_SupportedNumChannels.\n", rv);
//     return rv;
//   }
//   assert(size > 0 && writable);
//
//   AUChannelInfo* info = (AUChannelInfo*) malloc(size);
//   rv = AudioUnitGetProperty(au,
//                             kAudioUnitProperty_SupportedNumChannels,
//                             kAudioUnitScope_Global,
//                             AU_OUT_BUS,
//                             info,
//                             &size);
//   if (rv != noErr) {
//     LOG("%d: Could not get kAudioUnitProperty_SupportedNumChannels.\n", rv);
//     return rv;
//   }
//   LOG("input channels: %d, output channels: %d\n", info->inChannels, info->outChannels);
//   free(info);
//
//   return rv;
// }

OSStatus
get_channel_layout(bool preferred)
{
  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.\n", rv);
    return rv;
  }

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

  // Get the current format
  AudioStreamBasicDescription format;
  size = sizeof(format);
  rv = AudioUnitGetProperty(outputUnit,
                            kAudioUnitProperty_StreamFormat,
                            kAudioUnitScope_Output,
                            AU_OUT_BUS,
                            &format,
                            &size);
  if (rv != noErr) {
    LOG("%d: Could not get current audio output format.\n", rv);
  }
  LOG("Output device sampling rate: %.2f with %d channels.\n", format.mSampleRate, format.mChannelsPerFrame);

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

  AudioChannelLayout* layout = (AudioChannelLayout*) malloc(size);
  rv = AudioUnitGetProperty(outputUnit,
                            (preferred) ? kAudioDevicePropertyPreferredChannelLayout : kAudioUnitProperty_AudioChannelLayout,
                            kAudioUnitScope_Output,
                            AU_OUT_BUS,
                            layout,
                            &size);
  if (rv != noErr) {
    LOG("%d: Could not get %s.\n", rv, (preferred) ? "kAudioDevicePropertyPreferredChannelLayout" : "kAudioUnitProperty_AudioChannelLayout");
    return rv;
  }

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

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

  return rv;
}

int main()
{
  get_channel_layout(false);
  get_channel_layout(true);
  // get_number_of_supported_channels();
  return 0;
}