media/libcubeb/src/cubeb_audiounit.cpp
author Alex Chronopoulos <achronop@gmail.com>
Fri, 12 Oct 2018 13:31:18 +0300
changeset 499319 fbf50f6e40718aa2c8e1e1116e858ac5a3d3e26e
parent 495407 169eb24672a7f9948bc61875da50243229765a5f
child 500734 37df3d44e6882b69f9b8eda9ca67b5d322272fa7
permissions -rw-r--r--
Bug 1498519 - Update cubeb from upstream to 4559815. r=padenot Differential Revision: https://phabricator.services.mozilla.com/D8527

/*
 * Copyright © 2011 Mozilla Foundation
 *
 * This program is made available under an ISC-style license.  See the
 * accompanying file LICENSE for details.
 */
#undef NDEBUG

#include <TargetConditionals.h>
#include <assert.h>
#include <mach/mach_time.h>
#include <pthread.h>
#include <stdlib.h>
#include <AudioUnit/AudioUnit.h>
#if !TARGET_OS_IPHONE
#include <AvailabilityMacros.h>
#include <CoreAudio/AudioHardware.h>
#include <CoreAudio/HostTime.h>
#include <CoreFoundation/CoreFoundation.h>
#endif
#include <CoreAudio/CoreAudioTypes.h>
#include <AudioToolbox/AudioToolbox.h>
#include "cubeb/cubeb.h"
#include "cubeb-internal.h"
#include "cubeb_mixer.h"
#include "cubeb_panner.h"
#if !TARGET_OS_IPHONE
#include "cubeb_osx_run_loop.h"
#endif
#include "cubeb_resampler.h"
#include "cubeb_ring_array.h"
#include <algorithm>
#include <atomic>
#include <vector>
#include <set>
#include <sys/time.h>
#include <string>

using namespace std;

#if MAC_OS_X_VERSION_MIN_REQUIRED < 101000
typedef UInt32 AudioFormatFlags;
#endif

#define AU_OUT_BUS    0
#define AU_IN_BUS     1

const char * DISPATCH_QUEUE_LABEL = "org.mozilla.cubeb";
const char * PRIVATE_AGGREGATE_DEVICE_NAME = "CubebAggregateDevice";

#ifdef ALOGV
#undef ALOGV
#endif
#define ALOGV(msg, ...) dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{LOGV(msg, ##__VA_ARGS__);})

#ifdef ALOG
#undef ALOG
#endif
#define ALOG(msg, ...) dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{LOG(msg, ##__VA_ARGS__);})

/* Testing empirically, some headsets report a minimal latency that is very
 * low, but this does not work in practice. Lie and say the minimum is 256
 * frames. */
const uint32_t SAFE_MIN_LATENCY_FRAMES = 256;
const uint32_t SAFE_MAX_LATENCY_FRAMES = 512;

const AudioObjectPropertyAddress DEFAULT_INPUT_DEVICE_PROPERTY_ADDRESS = {
  kAudioHardwarePropertyDefaultInputDevice,
  kAudioObjectPropertyScopeGlobal,
  kAudioObjectPropertyElementMaster
};

const AudioObjectPropertyAddress DEFAULT_OUTPUT_DEVICE_PROPERTY_ADDRESS = {
  kAudioHardwarePropertyDefaultOutputDevice,
  kAudioObjectPropertyScopeGlobal,
  kAudioObjectPropertyElementMaster
};

const AudioObjectPropertyAddress DEVICE_IS_ALIVE_PROPERTY_ADDRESS = {
  kAudioDevicePropertyDeviceIsAlive,
  kAudioObjectPropertyScopeGlobal,
  kAudioObjectPropertyElementMaster
};

const AudioObjectPropertyAddress DEVICES_PROPERTY_ADDRESS = {
  kAudioHardwarePropertyDevices,
  kAudioObjectPropertyScopeGlobal,
  kAudioObjectPropertyElementMaster
};

const AudioObjectPropertyAddress INPUT_DATA_SOURCE_PROPERTY_ADDRESS = {
  kAudioDevicePropertyDataSource,
  kAudioDevicePropertyScopeInput,
  kAudioObjectPropertyElementMaster
};

const AudioObjectPropertyAddress OUTPUT_DATA_SOURCE_PROPERTY_ADDRESS = {
  kAudioDevicePropertyDataSource,
  kAudioDevicePropertyScopeOutput,
  kAudioObjectPropertyElementMaster
};

typedef uint32_t device_flags_value;

enum device_flags {
  DEV_UNKNOWN           = 0x00, /* Unknown */
  DEV_INPUT             = 0x01, /* Record device like mic */
  DEV_OUTPUT            = 0x02, /* Playback device like speakers */
  DEV_SYSTEM_DEFAULT    = 0x04, /* System default device */
  DEV_SELECTED_DEFAULT  = 0x08, /* User selected to use the system default device */
};

void audiounit_stream_stop_internal(cubeb_stream * stm);
void audiounit_stream_start_internal(cubeb_stream * stm);
static void audiounit_close_stream(cubeb_stream *stm);
static int audiounit_setup_stream(cubeb_stream *stm);
static vector<AudioObjectID>
audiounit_get_devices_of_type(cubeb_device_type devtype);
static UInt32 audiounit_get_device_presentation_latency(AudioObjectID devid, AudioObjectPropertyScope scope);

#if !TARGET_OS_IPHONE
static AudioObjectID audiounit_get_default_device_id(cubeb_device_type type);
static int audiounit_uninstall_device_changed_callback(cubeb_stream * stm);
static int audiounit_uninstall_system_changed_callback(cubeb_stream * stm);
static void audiounit_reinit_stream_async(cubeb_stream * stm, device_flags_value flags);
#endif

extern cubeb_ops const audiounit_ops;

struct cubeb {
  cubeb_ops const * ops = &audiounit_ops;
  owned_critical_section mutex;
  int active_streams = 0;
  uint32_t global_latency_frames = 0;
  cubeb_device_collection_changed_callback collection_changed_callback = nullptr;
  void * collection_changed_user_ptr = nullptr;
  /* Differentiate input from output devices. */
  cubeb_device_type collection_changed_devtype = CUBEB_DEVICE_TYPE_UNKNOWN;
  vector<AudioObjectID> devtype_device_array;
  // The queue is asynchronously deallocated once all references to it are released
  dispatch_queue_t serial_queue = dispatch_queue_create(DISPATCH_QUEUE_LABEL, DISPATCH_QUEUE_SERIAL);
  // Current used channel layout
  atomic<cubeb_channel_layout> layout{ CUBEB_LAYOUT_UNDEFINED };
  uint32_t channels = 0;
};

static unique_ptr<AudioChannelLayout, decltype(&free)>
make_sized_audio_channel_layout(size_t sz)
{
    assert(sz >= sizeof(AudioChannelLayout));
    AudioChannelLayout * acl = reinterpret_cast<AudioChannelLayout *>(calloc(1, sz));
    assert(acl); // Assert the allocation works.
    return unique_ptr<AudioChannelLayout, decltype(&free)>(acl, free);
}

enum class io_side {
  INPUT,
  OUTPUT,
};

static char const *
to_string(io_side side)
{
  switch (side) {
  case io_side::INPUT:
    return "input";
  case io_side::OUTPUT:
    return "output";
  }
}

struct device_info {
  AudioDeviceID id = kAudioObjectUnknown;
  device_flags_value flags = DEV_UNKNOWN;
};

struct property_listener {
  AudioDeviceID device_id;
  const AudioObjectPropertyAddress * property_address;
  AudioObjectPropertyListenerProc callback;
  cubeb_stream * stream;

  property_listener(AudioDeviceID id,
                    const AudioObjectPropertyAddress * address,
                    AudioObjectPropertyListenerProc proc,
                    cubeb_stream * stm)
    : device_id(id)
    , property_address(address)
    , callback(proc)
    , stream(stm)
  {}
};

struct cubeb_stream {
  explicit cubeb_stream(cubeb * context);

  /* Note: Must match cubeb_stream layout in cubeb.c. */
  cubeb * context;
  void * user_ptr = nullptr;
  /**/

  cubeb_data_callback data_callback = nullptr;
  cubeb_state_callback state_callback = nullptr;
  cubeb_device_changed_callback device_changed_callback = nullptr;
  owned_critical_section device_changed_callback_lock;
  /* Stream creation parameters */
  cubeb_stream_params input_stream_params = { CUBEB_SAMPLE_FLOAT32NE, 0, 0, CUBEB_LAYOUT_UNDEFINED, CUBEB_STREAM_PREF_NONE };
  cubeb_stream_params output_stream_params = { CUBEB_SAMPLE_FLOAT32NE, 0, 0, CUBEB_LAYOUT_UNDEFINED, CUBEB_STREAM_PREF_NONE };
  device_info input_device;
  device_info output_device;
  /* Format descriptions */
  AudioStreamBasicDescription input_desc;
  AudioStreamBasicDescription output_desc;
  /* I/O AudioUnits */
  AudioUnit input_unit = nullptr;
  AudioUnit output_unit = nullptr;
  /* I/O device sample rate */
  Float64 input_hw_rate = 0;
  Float64 output_hw_rate = 0;
  /* Expected I/O thread interleave,
   * calculated from I/O hw rate. */
  int expected_output_callbacks_in_a_row = 0;
  owned_critical_section mutex;
  // Hold the input samples in every input callback iteration.
  // Only accessed on input/output callback thread and during initial configure.
  unique_ptr<auto_array_wrapper> input_linear_buffer;
  /* Frame counters */
  atomic<uint64_t> frames_played{ 0 };
  uint64_t frames_queued = 0;
  // How many frames got read from the input since the stream started (includes
  // padded silence)
  atomic<int64_t> frames_read{ 0 };
  // How many frames got written to the output device since the stream started
  atomic<int64_t> frames_written{ 0 };
  atomic<bool> shutdown{ true };
  atomic<bool> draining{ false };
  atomic<bool> reinit_pending { false };
  atomic<bool> destroy_pending{ false };
  /* Latency requested by the user. */
  uint32_t latency_frames = 0;
  atomic<uint32_t> current_latency_frames{ 0 };
  atomic<float> panning{ 0 };
  unique_ptr<cubeb_resampler, decltype(&cubeb_resampler_destroy)> resampler;
  /* This is true if a device change callback is currently running.  */
  atomic<bool> switching_device{ false };
  atomic<bool> buffer_size_change_state{ false };
  AudioDeviceID aggregate_device_id = 0;    // the aggregate device id
  AudioObjectID plugin_id = 0;              // used to create aggregate device
  /* Mixer interface */
  unique_ptr<cubeb_mixer, decltype(&cubeb_mixer_destroy)> mixer;
  /* Buffer where remixing/resampling will occur when upmixing is required */
  /* Only accessed from callback thread */
  unique_ptr<uint8_t[]> temp_buffer;
  size_t temp_buffer_size = 0; // size in bytes.
  /* Listeners indicating what system events are monitored. */
  unique_ptr<property_listener> default_input_listener;
  unique_ptr<property_listener> default_output_listener;
  unique_ptr<property_listener> input_alive_listener;
  unique_ptr<property_listener> input_source_listener;
  unique_ptr<property_listener> output_source_listener;
};

bool has_input(cubeb_stream * stm)
{
  return stm->input_stream_params.rate != 0;
}

bool has_output(cubeb_stream * stm)
{
  return stm->output_stream_params.rate != 0;
}

cubeb_channel
channel_label_to_cubeb_channel(UInt32 label)
{
  switch (label) {
    case kAudioChannelLabel_Left:
      return CHANNEL_FRONT_LEFT;
    case kAudioChannelLabel_Right:
      return CHANNEL_FRONT_RIGHT;
    case kAudioChannelLabel_Center:
      return CHANNEL_FRONT_CENTER;
    case kAudioChannelLabel_LFEScreen:
      return CHANNEL_LOW_FREQUENCY;
    case kAudioChannelLabel_LeftSurround:
      return CHANNEL_BACK_LEFT;
    case kAudioChannelLabel_RightSurround:
      return CHANNEL_BACK_RIGHT;
    case kAudioChannelLabel_LeftCenter:
      return CHANNEL_FRONT_LEFT_OF_CENTER;
    case kAudioChannelLabel_RightCenter:
      return CHANNEL_FRONT_RIGHT_OF_CENTER;
    case kAudioChannelLabel_CenterSurround:
      return CHANNEL_BACK_CENTER;
    case kAudioChannelLabel_LeftSurroundDirect:
      return CHANNEL_SIDE_LEFT;
    case kAudioChannelLabel_RightSurroundDirect:
      return CHANNEL_SIDE_RIGHT;
    case kAudioChannelLabel_TopCenterSurround:
      return CHANNEL_TOP_CENTER;
    case kAudioChannelLabel_VerticalHeightLeft:
      return CHANNEL_TOP_FRONT_LEFT;
    case kAudioChannelLabel_VerticalHeightCenter:
      return CHANNEL_TOP_FRONT_CENTER;
    case kAudioChannelLabel_VerticalHeightRight:
      return CHANNEL_TOP_FRONT_RIGHT;
    case kAudioChannelLabel_TopBackLeft:
      return CHANNEL_TOP_BACK_LEFT;
    case kAudioChannelLabel_TopBackCenter:
      return CHANNEL_TOP_BACK_CENTER;
    case kAudioChannelLabel_TopBackRight:
      return CHANNEL_TOP_BACK_RIGHT;
    default:
      return CHANNEL_UNKNOWN;
  }
}

AudioChannelLabel
cubeb_channel_to_channel_label(cubeb_channel channel)
{
  switch (channel) {
    case CHANNEL_FRONT_LEFT:
      return kAudioChannelLabel_Left;
    case CHANNEL_FRONT_RIGHT:
      return kAudioChannelLabel_Right;
    case CHANNEL_FRONT_CENTER:
      return kAudioChannelLabel_Center;
    case CHANNEL_LOW_FREQUENCY:
      return kAudioChannelLabel_LFEScreen;
    case CHANNEL_BACK_LEFT:
      return kAudioChannelLabel_LeftSurround;
    case CHANNEL_BACK_RIGHT:
      return kAudioChannelLabel_RightSurround;
    case CHANNEL_FRONT_LEFT_OF_CENTER:
      return kAudioChannelLabel_LeftCenter;
    case CHANNEL_FRONT_RIGHT_OF_CENTER:
      return kAudioChannelLabel_RightCenter;
    case CHANNEL_BACK_CENTER:
      return kAudioChannelLabel_CenterSurround;
    case CHANNEL_SIDE_LEFT:
      return kAudioChannelLabel_LeftSurroundDirect;
    case CHANNEL_SIDE_RIGHT:
      return kAudioChannelLabel_RightSurroundDirect;
    case CHANNEL_TOP_CENTER:
      return kAudioChannelLabel_TopCenterSurround;
    case CHANNEL_TOP_FRONT_LEFT:
      return kAudioChannelLabel_VerticalHeightLeft;
    case CHANNEL_TOP_FRONT_CENTER:
      return kAudioChannelLabel_VerticalHeightCenter;
    case CHANNEL_TOP_FRONT_RIGHT:
      return kAudioChannelLabel_VerticalHeightRight;
    case CHANNEL_TOP_BACK_LEFT:
      return kAudioChannelLabel_TopBackLeft;
    case CHANNEL_TOP_BACK_CENTER:
      return kAudioChannelLabel_TopBackCenter;
    case CHANNEL_TOP_BACK_RIGHT:
      return kAudioChannelLabel_TopBackRight;
    default:
      return kAudioChannelLabel_Unknown;
  }
}

#if TARGET_OS_IPHONE
typedef UInt32 AudioDeviceID;
typedef UInt32 AudioObjectID;

#define AudioGetCurrentHostTime mach_absolute_time

uint64_t
AudioConvertHostTimeToNanos(uint64_t host_time)
{
  static struct mach_timebase_info timebase_info;
  static bool initialized = false;
  if (!initialized) {
    mach_timebase_info(&timebase_info);
    initialized = true;
  }

  long double answer = host_time;
  if (timebase_info.numer != timebase_info.denom) {
    answer *= timebase_info.numer;
    answer /= timebase_info.denom;
  }
  return (uint64_t)answer;
}
#endif

static void
audiounit_increment_active_streams(cubeb * ctx)
{
  ctx->mutex.assert_current_thread_owns();
  ctx->active_streams += 1;
}

static void
audiounit_decrement_active_streams(cubeb * ctx)
{
  ctx->mutex.assert_current_thread_owns();
  ctx->active_streams -= 1;
}

static int
audiounit_active_streams(cubeb * ctx)
{
  ctx->mutex.assert_current_thread_owns();
  return ctx->active_streams;
}

static void
audiounit_set_global_latency(cubeb * ctx, uint32_t latency_frames)
{
  ctx->mutex.assert_current_thread_owns();
  assert(audiounit_active_streams(ctx) == 1);
  ctx->global_latency_frames = latency_frames;
}

static void
audiounit_make_silent(AudioBuffer * ioData)
{
  assert(ioData);
  assert(ioData->mData);
  memset(ioData->mData, 0, ioData->mDataByteSize);
}

static OSStatus
audiounit_render_input(cubeb_stream * stm,
                       AudioUnitRenderActionFlags * flags,
                       AudioTimeStamp const * tstamp,
                       UInt32 bus,
                       UInt32 input_frames)
{
  /* Create the AudioBufferList to store input. */
  AudioBufferList input_buffer_list;
  input_buffer_list.mBuffers[0].mDataByteSize =
      stm->input_desc.mBytesPerFrame * input_frames;
  input_buffer_list.mBuffers[0].mData = nullptr;
  input_buffer_list.mBuffers[0].mNumberChannels = stm->input_desc.mChannelsPerFrame;
  input_buffer_list.mNumberBuffers = 1;

  /* Render input samples */
  OSStatus r = AudioUnitRender(stm->input_unit,
                               flags,
                               tstamp,
                               bus,
                               input_frames,
                               &input_buffer_list);

  if (r != noErr) {
    LOG("AudioUnitRender rv=%d", r);
    if (r != kAudioUnitErr_CannotDoInCurrentContext) {
      return r;
    }
    if (stm->output_unit) {
      // kAudioUnitErr_CannotDoInCurrentContext is returned when using a BT
      // headset and the profile is changed from A2DP to HFP/HSP. The previous
      // output device is no longer valid and must be reset.
      audiounit_reinit_stream_async(stm, DEV_INPUT | DEV_OUTPUT);
    }
    // For now state that no error occurred and feed silence, stream will be
    // resumed once reinit has completed.
    ALOGV("(%p) input: reinit pending feeding silence instead", stm);
    stm->input_linear_buffer->push_silence(input_frames * stm->input_desc.mChannelsPerFrame);
  } else {
    /* Copy input data in linear buffer. */
    stm->input_linear_buffer->push(input_buffer_list.mBuffers[0].mData,
                                   input_frames * stm->input_desc.mChannelsPerFrame);
  }

  /* Advance input frame counter. */
  assert(input_frames > 0);
  stm->frames_read += input_frames;

  ALOGV("(%p) input: buffers %u, size %u, channels %u, rendered frames %d, total frames %lu.",
        stm,
        (unsigned int) input_buffer_list.mNumberBuffers,
        (unsigned int) input_buffer_list.mBuffers[0].mDataByteSize,
        (unsigned int) input_buffer_list.mBuffers[0].mNumberChannels,
        (unsigned int) input_frames,
        stm->input_linear_buffer->length() / stm->input_desc.mChannelsPerFrame);

  return noErr;
}

static OSStatus
audiounit_input_callback(void * user_ptr,
                         AudioUnitRenderActionFlags * flags,
                         AudioTimeStamp const * tstamp,
                         UInt32 bus,
                         UInt32 input_frames,
                         AudioBufferList * /* bufs */)
{
  cubeb_stream * stm = static_cast<cubeb_stream *>(user_ptr);

  assert(stm->input_unit != NULL);
  assert(AU_IN_BUS == bus);

  if (stm->shutdown) {
    ALOG("(%p) input shutdown", stm);
    return noErr;
  }

  OSStatus r = audiounit_render_input(stm, flags, tstamp, bus, input_frames);
  if (r != noErr) {
    return r;
  }

  // Full Duplex. We'll call data_callback in the AudioUnit output callback.
  if (stm->output_unit != NULL) {
    return noErr;
  }

  /* Input only. Call the user callback through resampler.
     Resampler will deliver input buffer in the correct rate. */
  assert(input_frames <= stm->input_linear_buffer->length() / stm->input_desc.mChannelsPerFrame);
  long total_input_frames = stm->input_linear_buffer->length() / stm->input_desc.mChannelsPerFrame;
  long outframes = cubeb_resampler_fill(stm->resampler.get(),
                                        stm->input_linear_buffer->data(),
                                        &total_input_frames,
                                        NULL,
                                        0);
  if (outframes < total_input_frames) {
    OSStatus r = AudioOutputUnitStop(stm->input_unit);
    assert(r == 0);
    stm->state_callback(stm, stm->user_ptr, CUBEB_STATE_DRAINED);
    return noErr;
  }

  // Reset input buffer
  stm->input_linear_buffer->clear();

  return noErr;
}

static void
audiounit_mix_output_buffer(cubeb_stream * stm,
                            size_t output_frames,
                            void * input_buffer,
                            size_t input_buffer_size,
                            void * output_buffer,
                            size_t output_buffer_size)
{
  assert(input_buffer_size >=
         cubeb_sample_size(stm->output_stream_params.format) *
           stm->output_stream_params.channels * output_frames);
  assert(output_buffer_size >= stm->output_desc.mBytesPerFrame * output_frames);

  int r = cubeb_mixer_mix(stm->mixer.get(),
                          output_frames,
                          input_buffer,
                          input_buffer_size,
                          output_buffer,
                          output_buffer_size);
  if (r != 0) {
    LOG("Remix error = %d", r);
  }
}

// Return how many input frames (sampled at input_hw_rate) are needed to provide
// output_frames (sampled at output_stream_params.rate)
static int64_t
minimum_resampling_input_frames(cubeb_stream * stm, uint32_t output_frames)
{
  if (stm->input_hw_rate == stm->output_stream_params.rate) {
    // Fast path.
    return output_frames;
  }
  return ceil(stm->input_hw_rate * output_frames /
              stm->output_stream_params.rate);
}

static OSStatus
audiounit_output_callback(void * user_ptr,
                          AudioUnitRenderActionFlags * /* flags */,
                          AudioTimeStamp const * tstamp,
                          UInt32 bus,
                          UInt32 output_frames,
                          AudioBufferList * outBufferList)
{
  assert(AU_OUT_BUS == bus);
  assert(outBufferList->mNumberBuffers == 1);

  cubeb_stream * stm = static_cast<cubeb_stream *>(user_ptr);

  ALOGV("(%p) output: buffers %u, size %u, channels %u, frames %u, total input frames %lu.",
        stm,
        (unsigned int) outBufferList->mNumberBuffers,
        (unsigned int) outBufferList->mBuffers[0].mDataByteSize,
        (unsigned int) outBufferList->mBuffers[0].mNumberChannels,
        (unsigned int) output_frames,
        has_input(stm) ? stm->input_linear_buffer->length() / stm->input_desc.mChannelsPerFrame : 0);

  long input_frames = 0;
  void * output_buffer = NULL, * input_buffer = NULL;

  if (stm->shutdown) {
    ALOG("(%p) output shutdown.", stm);
    audiounit_make_silent(&outBufferList->mBuffers[0]);
    return noErr;
  }

  if (stm->draining) {
    OSStatus r = AudioOutputUnitStop(stm->output_unit);
    assert(r == 0);
    if (stm->input_unit) {
      r = AudioOutputUnitStop(stm->input_unit);
      assert(r == 0);
    }
    stm->state_callback(stm, stm->user_ptr, CUBEB_STATE_DRAINED);
    audiounit_make_silent(&outBufferList->mBuffers[0]);
    return noErr;
  }

  /* Get output buffer. */
  if (stm->mixer) {
    // If remixing needs to occur, we can't directly work in our final
    // destination buffer as data may be overwritten or too small to start with.
    size_t size_needed = output_frames * stm->output_stream_params.channels *
                         cubeb_sample_size(stm->output_stream_params.format);
    if (stm->temp_buffer_size < size_needed) {
      stm->temp_buffer.reset(new uint8_t[size_needed]);
      stm->temp_buffer_size = size_needed;
    }
    output_buffer = stm->temp_buffer.get();
  } else {
    output_buffer = outBufferList->mBuffers[0].mData;
  }

  stm->frames_written += output_frames;

  /* If Full duplex get also input buffer */
  if (stm->input_unit != NULL) {
    /* If the output callback came first and this is a duplex stream, we need to
     * fill in some additional silence in the resampler.
     * Otherwise, if we had more than expected callbacks in a row, or we're
     * currently switching, we add some silence as well to compensate for the
     * fact that we're lacking some input data. */
    uint32_t input_frames_needed =
      minimum_resampling_input_frames(stm, stm->frames_written);
    long missing_frames = input_frames_needed - stm->frames_read;
    if (missing_frames > 0) {
      stm->input_linear_buffer->push_silence(missing_frames * stm->input_desc.mChannelsPerFrame);
      stm->frames_read = input_frames_needed;

      ALOG("(%p) %s pushed %ld frames of input silence.", stm, stm->frames_read == 0 ? "Input hasn't started," :
           stm->switching_device ? "Device switching," : "Drop out,", missing_frames);
    }
    input_buffer = stm->input_linear_buffer->data();
    // Number of input frames in the buffer. It will change to actually used frames
    // inside fill
    input_frames = stm->input_linear_buffer->length() / stm->input_desc.mChannelsPerFrame;
  }

  /* Call user callback through resampler. */
  long outframes = cubeb_resampler_fill(stm->resampler.get(),
                                        input_buffer,
                                        input_buffer ? &input_frames : NULL,
                                        output_buffer,
                                        output_frames);

  if (input_buffer) {
    // Pop from the buffer the frames used by the the resampler.
    stm->input_linear_buffer->pop(input_frames * stm->input_desc.mChannelsPerFrame);
  }

  if (outframes < 0 || outframes > output_frames) {
    stm->shutdown = true;
    OSStatus r = AudioOutputUnitStop(stm->output_unit);
    assert(r == 0);
    if (stm->input_unit) {
      r = AudioOutputUnitStop(stm->input_unit);
      assert(r == 0);
    }
    stm->state_callback(stm, stm->user_ptr, CUBEB_STATE_ERROR);
    audiounit_make_silent(&outBufferList->mBuffers[0]);
    return noErr;
  }

  stm->draining = (UInt32) outframes < output_frames;
  stm->frames_played = stm->frames_queued;
  stm->frames_queued += outframes;

  AudioFormatFlags outaff = stm->output_desc.mFormatFlags;
  float panning = (stm->output_desc.mChannelsPerFrame == 2) ?
      stm->panning.load(memory_order_relaxed) : 0.0f;

  /* Post process output samples. */
  if (stm->draining) {
    size_t outbpf = cubeb_sample_size(stm->output_stream_params.format);
    /* Clear missing frames (silence) */
    memset((uint8_t*)output_buffer + outframes * outbpf, 0, (output_frames - outframes) * outbpf);
  }

  /* Mixing */
  if (stm->mixer) {
    audiounit_mix_output_buffer(stm,
                                output_frames,
                                output_buffer,
                                stm->temp_buffer_size,
                                outBufferList->mBuffers[0].mData,
                                outBufferList->mBuffers[0].mDataByteSize);
  } else {
    /* Pan stereo. */
    if (panning != 0.0f) {
      if (outaff & kAudioFormatFlagIsFloat) {
        cubeb_pan_stereo_buffer_float(
          (float*)output_buffer, outframes, panning);
      } else if (outaff & kAudioFormatFlagIsSignedInteger) {
        cubeb_pan_stereo_buffer_int((short*)output_buffer, outframes, panning);
      }
    }
  }

  return noErr;
}

extern "C" {
int
audiounit_init(cubeb ** context, char const * /* context_name */)
{
#if !TARGET_OS_IPHONE
  cubeb_set_coreaudio_notification_runloop();
#endif

  *context = new cubeb;

  return CUBEB_OK;
}
}

static char const *
audiounit_get_backend_id(cubeb * /* ctx */)
{
  return "audiounit";
}

#if !TARGET_OS_IPHONE

static int audiounit_stream_get_volume(cubeb_stream * stm, float * volume);
static int audiounit_stream_set_volume(cubeb_stream * stm, float volume);

static int
audiounit_set_device_info(cubeb_stream * stm, AudioDeviceID id, io_side side)
{
  assert(stm);

  device_info * info = nullptr;
  cubeb_device_type type = CUBEB_DEVICE_TYPE_UNKNOWN;

  if (side == io_side::INPUT) {
    info = &stm->input_device;
    type = CUBEB_DEVICE_TYPE_INPUT;
  } else if (side == io_side::OUTPUT) {
    info = &stm->output_device;
    type = CUBEB_DEVICE_TYPE_OUTPUT;
  }
  memset(info, 0, sizeof(device_info));
  info->id = id;

  if (side == io_side::INPUT) {
    info->flags |= DEV_INPUT;
  } else if (side == io_side::OUTPUT) {
    info->flags |= DEV_OUTPUT;
  }

  AudioDeviceID default_device_id = audiounit_get_default_device_id(type);
  if (default_device_id == kAudioObjectUnknown) {
    return CUBEB_ERROR;
  }
  if (id == kAudioObjectUnknown) {
    info->id = default_device_id;
    info->flags |= DEV_SELECTED_DEFAULT;
  }

  if (info->id == default_device_id) {
    info->flags |= DEV_SYSTEM_DEFAULT;
  }

  assert(info->id);
  assert(info->flags & DEV_INPUT && !(info->flags & DEV_OUTPUT) ||
           !(info->flags & DEV_INPUT) && info->flags & DEV_OUTPUT);

  return CUBEB_OK;
}


static int
audiounit_reinit_stream(cubeb_stream * stm, device_flags_value flags)
{
  auto_lock context_lock(stm->context->mutex);
  assert((flags & DEV_INPUT && stm->input_unit) ||
         (flags & DEV_OUTPUT && stm->output_unit));
  if (!stm->shutdown) {
    audiounit_stream_stop_internal(stm);
  }

  int r = audiounit_uninstall_device_changed_callback(stm);
  if (r != CUBEB_OK) {
    LOG("(%p) Could not uninstall all device change listeners.", stm);
  }

  {
    auto_lock lock(stm->mutex);
    float volume = 0.0;
    int vol_rv = CUBEB_ERROR;
    if (stm->output_unit) {
      vol_rv = audiounit_stream_get_volume(stm, &volume);
    }

    audiounit_close_stream(stm);

    /* Reinit occurs in one of the following case:
     * - When the device is not alive any more
     * - When the default system device change.
     * - The bluetooth device changed from A2DP to/from HFP/HSP profile
     * We first attempt to re-use the same device id, should that fail we will
     * default to the (potentially new) default device. */
    AudioDeviceID input_device = flags & DEV_INPUT ? stm->input_device.id : 0;
    if (flags & DEV_INPUT) {
      r = audiounit_set_device_info(stm, input_device, io_side::INPUT);
      if (r != CUBEB_OK) {
        LOG("(%p) Set input device info failed. This can happen when last media device is unplugged", stm);
        return CUBEB_ERROR;
      }
    }

    /* Always use the default output on reinit. This is not correct in every
     * case but it is sufficient for Firefox and prevent reinit from reporting
     * failures. It will change soon when reinit mechanism will be updated. */
    r = audiounit_set_device_info(stm, 0, io_side::OUTPUT);
    if (r != CUBEB_OK) {
      LOG("(%p) Set output device info failed. This can happen when last media device is unplugged", stm);
      return CUBEB_ERROR;
    }

    if (audiounit_setup_stream(stm) != CUBEB_OK) {
      LOG("(%p) Stream reinit failed.", stm);
      if (flags & DEV_INPUT && input_device != 0) {
        // Attempt to re-use the same device-id failed, so attempt again with
        // default input device.
        if (audiounit_set_device_info(stm, 0, io_side::INPUT) != CUBEB_OK ||
            audiounit_setup_stream(stm) != CUBEB_OK) {
          LOG("(%p) Second stream reinit failed.", stm);
          return CUBEB_ERROR;
        }
      }
    }

    if (vol_rv == CUBEB_OK) {
      audiounit_stream_set_volume(stm, volume);
    }

    // If the stream was running, start it again.
    if (!stm->shutdown) {
      audiounit_stream_start_internal(stm);
    }
  }
  return CUBEB_OK;
}

static void
audiounit_reinit_stream_async(cubeb_stream * stm, device_flags_value flags)
{
  if (std::atomic_exchange(&stm->reinit_pending, true)) {
    // A reinit task is already pending, nothing more to do.
    ALOG("(%p) re-init stream task already pending, cancelling request ", stm);
    return;
  }

  // Use a new thread, through the queue, to avoid deadlock when calling
  // Get/SetProperties method from inside notify callback
  dispatch_async(stm->context->serial_queue, ^() {
    if (stm->destroy_pending) {
      ALOG("(%p) stream pending destroy, cancelling reinit task", stm);
      return;
    }

    if (audiounit_reinit_stream(stm, flags) != CUBEB_OK) {
      if (audiounit_uninstall_system_changed_callback(stm) != CUBEB_OK) {
        LOG("(%p) Could not uninstall system changed callback", stm);
      }
      stm->state_callback(stm, stm->user_ptr, CUBEB_STATE_ERROR);
      LOG("(%p) Could not reopen the stream after switching.", stm);
    }
    stm->switching_device = false;
    stm->reinit_pending = false;
  });
}

static char const *
event_addr_to_string(AudioObjectPropertySelector selector)
{
  switch(selector) {
    case kAudioHardwarePropertyDefaultOutputDevice:
      return "kAudioHardwarePropertyDefaultOutputDevice";
    case kAudioHardwarePropertyDefaultInputDevice:
      return "kAudioHardwarePropertyDefaultInputDevice";
    case kAudioDevicePropertyDeviceIsAlive:
      return "kAudioDevicePropertyDeviceIsAlive";
    case kAudioDevicePropertyDataSource:
      return "kAudioDevicePropertyDataSource";
    default:
      return "Unknown";
  }
}

static OSStatus
audiounit_property_listener_callback(AudioObjectID id, UInt32 address_count,
                                     const AudioObjectPropertyAddress * addresses,
                                     void * user)
{
  cubeb_stream * stm = (cubeb_stream*) user;
  if (stm->switching_device) {
    LOG("Switching is already taking place. Skip Event %s for id=%d", event_addr_to_string(addresses[0].mSelector), id);
    return noErr;
  }
  stm->switching_device = true;

  LOG("(%p) Audio device changed, %u events.", stm, (unsigned int) address_count);
  for (UInt32 i = 0; i < address_count; i++) {
    switch(addresses[i].mSelector) {
      case kAudioHardwarePropertyDefaultOutputDevice: {
          LOG("Event[%u] - mSelector == kAudioHardwarePropertyDefaultOutputDevice for id=%d", (unsigned int) i, id);
        }
        break;
      case kAudioHardwarePropertyDefaultInputDevice: {
          LOG("Event[%u] - mSelector == kAudioHardwarePropertyDefaultInputDevice for id=%d", (unsigned int) i, id);
        }
      break;
      case kAudioDevicePropertyDeviceIsAlive: {
          LOG("Event[%u] - mSelector == kAudioDevicePropertyDeviceIsAlive for id=%d", (unsigned int) i, id);
          // If this is the default input device ignore the event,
          // kAudioHardwarePropertyDefaultInputDevice will take care of the switch
          if (stm->input_device.flags & DEV_SYSTEM_DEFAULT) {
            LOG("It's the default input device, ignore the event");
            stm->switching_device = false;
            return noErr;
          }
        }
        break;
      case kAudioDevicePropertyDataSource: {
          LOG("Event[%u] - mSelector == kAudioHardwarePropertyDataSource for id=%d", (unsigned int) i, id);
        }
        break;
      default:
        LOG("Event[%u] - mSelector == Unexpected Event id %d, return", (unsigned int) i, addresses[i].mSelector);
        stm->switching_device = false;
        return noErr;
    }
  }

  // Allow restart to choose the new default
  device_flags_value switch_side = DEV_UNKNOWN;
  if (has_input(stm)) {
    switch_side |= DEV_INPUT;
  }
  if (has_output(stm)) {
    switch_side |= DEV_OUTPUT;
  }

  for (UInt32 i = 0; i < address_count; i++) {
    switch(addresses[i].mSelector) {
    case kAudioHardwarePropertyDefaultOutputDevice:
    case kAudioHardwarePropertyDefaultInputDevice:
    case kAudioDevicePropertyDeviceIsAlive:
      /* fall through */
    case kAudioDevicePropertyDataSource: {
        auto_lock dev_cb_lock(stm->device_changed_callback_lock);
        if (stm->device_changed_callback) {
          stm->device_changed_callback(stm->user_ptr);
        }
        break;
      }
    }
  }

  audiounit_reinit_stream_async(stm, switch_side);

  return noErr;
}

OSStatus
audiounit_add_listener(const property_listener * listener)
{
  assert(listener);
  return AudioObjectAddPropertyListener(listener->device_id,
                                        listener->property_address,
                                        listener->callback,
                                        listener->stream);
}

OSStatus
audiounit_remove_listener(const property_listener * listener)
{
  assert(listener);
  return AudioObjectRemovePropertyListener(listener->device_id,
                                           listener->property_address,
                                           listener->callback,
                                           listener->stream);
}

static int
audiounit_install_device_changed_callback(cubeb_stream * stm)
{
  OSStatus rv;
  int r = CUBEB_OK;

  if (stm->output_unit) {
    /* This event will notify us when the data source on the same device changes,
     * for example when the user plugs in a normal (non-usb) headset in the
     * headphone jack. */
    stm->output_source_listener.reset(new property_listener(
      stm->output_device.id, &OUTPUT_DATA_SOURCE_PROPERTY_ADDRESS,
      &audiounit_property_listener_callback, stm));
    rv = audiounit_add_listener(stm->output_source_listener.get());
    if (rv != noErr) {
      stm->output_source_listener.reset();
      LOG("AudioObjectAddPropertyListener/output/kAudioDevicePropertyDataSource rv=%d, device id=%d", rv, stm->output_device.id);
      r = CUBEB_ERROR;
    }
  }

  if (stm->input_unit) {
    /* This event will notify us when the data source on the input device changes. */
    stm->input_source_listener.reset(new property_listener(
      stm->input_device.id, &INPUT_DATA_SOURCE_PROPERTY_ADDRESS,
      &audiounit_property_listener_callback, stm));
    rv = audiounit_add_listener(stm->input_source_listener.get());
    if (rv != noErr) {
      stm->input_source_listener.reset();
      LOG("AudioObjectAddPropertyListener/input/kAudioDevicePropertyDataSource rv=%d, device id=%d", rv, stm->input_device.id);
      r = CUBEB_ERROR;
    }

    /* Event to notify when the input is going away. */
    stm->input_alive_listener.reset(new property_listener(
      stm->input_device.id, &DEVICE_IS_ALIVE_PROPERTY_ADDRESS,
      &audiounit_property_listener_callback, stm));
    rv = audiounit_add_listener(stm->input_alive_listener.get());
    if (rv != noErr) {
      stm->input_alive_listener.reset();
      LOG("AudioObjectAddPropertyListener/input/kAudioDevicePropertyDeviceIsAlive rv=%d, device id =%d", rv, stm->input_device.id);
      r = CUBEB_ERROR;
    }
  }

  return r;
}

static int
audiounit_install_system_changed_callback(cubeb_stream * stm)
{
  OSStatus r;

  if (stm->output_unit) {
    /* This event will notify us when the default audio device changes,
     * for example when the user plugs in a USB headset and the system chooses it
     * automatically as the default, or when another device is chosen in the
     * dropdown list. */
    stm->default_output_listener.reset(new property_listener(
      kAudioObjectSystemObject, &DEFAULT_OUTPUT_DEVICE_PROPERTY_ADDRESS,
      &audiounit_property_listener_callback, stm));
    r = audiounit_add_listener(stm->default_output_listener.get());
    if (r != noErr) {
      stm->default_output_listener.reset();
      LOG("AudioObjectAddPropertyListener/output/kAudioHardwarePropertyDefaultOutputDevice rv=%d", r);
      return CUBEB_ERROR;
    }
  }

  if (stm->input_unit) {
    /* This event will notify us when the default input device changes. */
    stm->default_input_listener.reset(new property_listener(
      kAudioObjectSystemObject, &DEFAULT_INPUT_DEVICE_PROPERTY_ADDRESS,
      &audiounit_property_listener_callback, stm));
    r = audiounit_add_listener(stm->default_input_listener.get());
    if (r != noErr) {
      stm->default_input_listener.reset();
      LOG("AudioObjectAddPropertyListener/input/kAudioHardwarePropertyDefaultInputDevice rv=%d", r);
      return CUBEB_ERROR;
    }
  }

  return CUBEB_OK;
}

static int
audiounit_uninstall_device_changed_callback(cubeb_stream * stm)
{
  OSStatus rv;
  // Failing to uninstall listeners is not a fatal error.
  int r = CUBEB_OK;

  if (stm->output_source_listener) {
    rv = audiounit_remove_listener(stm->output_source_listener.get());
    if (rv != noErr) {
      LOG("AudioObjectRemovePropertyListener/output/kAudioDevicePropertyDataSource rv=%d, device id=%d", rv, stm->output_device.id);
      r = CUBEB_ERROR;
    }
    stm->output_source_listener.reset();
  }

  if (stm->input_source_listener) {
    rv = audiounit_remove_listener(stm->input_source_listener.get());
    if (rv != noErr) {
      LOG("AudioObjectRemovePropertyListener/input/kAudioDevicePropertyDataSource rv=%d, device id=%d", rv, stm->input_device.id);
      r = CUBEB_ERROR;
    }
    stm->input_source_listener.reset();
  }

  if (stm->input_alive_listener) {
    rv = audiounit_remove_listener(stm->input_alive_listener.get());
    if (rv != noErr) {
      LOG("AudioObjectRemovePropertyListener/input/kAudioDevicePropertyDeviceIsAlive rv=%d, device id=%d", rv, stm->input_device.id);
      r = CUBEB_ERROR;
    }
    stm->input_alive_listener.reset();
  }

  return r;
}

static int
audiounit_uninstall_system_changed_callback(cubeb_stream * stm)
{
  OSStatus r;

  if (stm->default_output_listener) {
    r = audiounit_remove_listener(stm->default_output_listener.get());
    if (r != noErr) {
      return CUBEB_ERROR;
    }
    stm->default_output_listener.reset();
  }

  if (stm->default_input_listener) {
    r = audiounit_remove_listener(stm->default_input_listener.get());
    if (r != noErr) {
      return CUBEB_ERROR;
    }
    stm->default_input_listener.reset();
  }
  return CUBEB_OK;
}

/* Get the acceptable buffer size (in frames) that this device can work with. */
static int
audiounit_get_acceptable_latency_range(AudioValueRange * latency_range)
{
  UInt32 size;
  OSStatus r;
  AudioDeviceID output_device_id;
  AudioObjectPropertyAddress output_device_buffer_size_range = {
    kAudioDevicePropertyBufferFrameSizeRange,
    kAudioDevicePropertyScopeOutput,
    kAudioObjectPropertyElementMaster
  };

  output_device_id = audiounit_get_default_device_id(CUBEB_DEVICE_TYPE_OUTPUT);
  if (output_device_id == kAudioObjectUnknown) {
    LOG("Could not get default output device id.");
    return CUBEB_ERROR;
  }

  /* Get the buffer size range this device supports */
  size = sizeof(*latency_range);

  r = AudioObjectGetPropertyData(output_device_id,
                                 &output_device_buffer_size_range,
                                 0,
                                 NULL,
                                 &size,
                                 latency_range);
  if (r != noErr) {
    LOG("AudioObjectGetPropertyData/buffer size range rv=%d", r);
    return CUBEB_ERROR;
  }

  return CUBEB_OK;
}
#endif /* !TARGET_OS_IPHONE */

static AudioObjectID
audiounit_get_default_device_id(cubeb_device_type type)
{
  const AudioObjectPropertyAddress * adr;
  if (type == CUBEB_DEVICE_TYPE_OUTPUT) {
    adr = &DEFAULT_OUTPUT_DEVICE_PROPERTY_ADDRESS;
  } else if (type == CUBEB_DEVICE_TYPE_INPUT) {
    adr = &DEFAULT_INPUT_DEVICE_PROPERTY_ADDRESS;
  } else {
    return kAudioObjectUnknown;
  }

  AudioDeviceID devid;
  UInt32 size = sizeof(AudioDeviceID);
  if (AudioObjectGetPropertyData(kAudioObjectSystemObject,
                                 adr, 0, NULL, &size, &devid) != noErr) {
    return kAudioObjectUnknown;
  }

  return devid;
}

int
audiounit_get_max_channel_count(cubeb * ctx, uint32_t * max_channels)
{
#if TARGET_OS_IPHONE
  //TODO: [[AVAudioSession sharedInstance] maximumOutputNumberOfChannels]
  *max_channels = 2;
#else
  UInt32 size;
  OSStatus r;
  AudioDeviceID output_device_id;
  AudioStreamBasicDescription stream_format;
  AudioObjectPropertyAddress stream_format_address = {
    kAudioDevicePropertyStreamFormat,
    kAudioDevicePropertyScopeOutput,
    kAudioObjectPropertyElementMaster
  };

  assert(ctx && max_channels);

  output_device_id = audiounit_get_default_device_id(CUBEB_DEVICE_TYPE_OUTPUT);
  if (output_device_id == kAudioObjectUnknown) {
    return CUBEB_ERROR;
  }

  size = sizeof(stream_format);

  r = AudioObjectGetPropertyData(output_device_id,
                                 &stream_format_address,
                                 0,
                                 NULL,
                                 &size,
                                 &stream_format);
  if (r != noErr) {
    LOG("AudioObjectPropertyAddress/StreamFormat rv=%d", r);
    return CUBEB_ERROR;
  }

  *max_channels = stream_format.mChannelsPerFrame;
#endif
  return CUBEB_OK;
}

static int
audiounit_get_min_latency(cubeb * /* ctx */,
                          cubeb_stream_params /* params */,
                          uint32_t * latency_frames)
{
#if TARGET_OS_IPHONE
  //TODO: [[AVAudioSession sharedInstance] inputLatency]
  return CUBEB_ERROR_NOT_SUPPORTED;
#else
  AudioValueRange latency_range;
  if (audiounit_get_acceptable_latency_range(&latency_range) != CUBEB_OK) {
    LOG("Could not get acceptable latency range.");
    return CUBEB_ERROR;
  }

  *latency_frames = max<uint32_t>(latency_range.mMinimum,
                                       SAFE_MIN_LATENCY_FRAMES);
#endif

  return CUBEB_OK;
}

static int
audiounit_get_preferred_sample_rate(cubeb * /* ctx */, uint32_t * rate)
{
#if TARGET_OS_IPHONE
  //TODO
  return CUBEB_ERROR_NOT_SUPPORTED;
#else
  UInt32 size;
  OSStatus r;
  Float64 fsamplerate;
  AudioDeviceID output_device_id;
  AudioObjectPropertyAddress samplerate_address = {
    kAudioDevicePropertyNominalSampleRate,
    kAudioObjectPropertyScopeGlobal,
    kAudioObjectPropertyElementMaster
  };

  output_device_id = audiounit_get_default_device_id(CUBEB_DEVICE_TYPE_OUTPUT);
  if (output_device_id == kAudioObjectUnknown) {
    return CUBEB_ERROR;
  }

  size = sizeof(fsamplerate);
  r = AudioObjectGetPropertyData(output_device_id,
                                 &samplerate_address,
                                 0,
                                 NULL,
                                 &size,
                                 &fsamplerate);

  if (r != noErr) {
    return CUBEB_ERROR;
  }

  *rate = static_cast<uint32_t>(fsamplerate);
#endif
  return CUBEB_OK;
}

static cubeb_channel_layout
audiounit_convert_channel_layout(AudioChannelLayout * layout)
{
  // When having on or two channel, force mono or stereo. Some devices (namely,
  //  Bose QC35, mark 1 and 2), expose a single channel mapped to the right for
  //  some reason.
  if (layout->mNumberChannelDescriptions == 1) {
    return CUBEB_LAYOUT_MONO;
  } else if (layout->mNumberChannelDescriptions == 2) {
    return CUBEB_LAYOUT_STEREO;
  }

  if (layout->mChannelLayoutTag != kAudioChannelLayoutTag_UseChannelDescriptions) {
    // kAudioChannelLayoutTag_UseChannelBitmap
    // kAudioChannelLayoutTag_Mono
    // kAudioChannelLayoutTag_Stereo
    // ....
    LOG("Only handle UseChannelDescriptions for now.\n");
    return CUBEB_LAYOUT_UNDEFINED;
  }

  cubeb_channel_layout cl = 0;
  for (UInt32 i = 0; i < layout->mNumberChannelDescriptions; ++i) {
    cubeb_channel cc = channel_label_to_cubeb_channel(
      layout->mChannelDescriptions[i].mChannelLabel);
    if (cc == CHANNEL_UNKNOWN) {
      return CUBEB_LAYOUT_UNDEFINED;
    }
    cl |= cc;
  }

  return cl;
}

static cubeb_channel_layout
audiounit_get_preferred_channel_layout(AudioUnit output_unit)
{
  OSStatus rv = noErr;
  UInt32 size = 0;
  rv = AudioUnitGetPropertyInfo(output_unit,
                                kAudioDevicePropertyPreferredChannelLayout,
                                kAudioUnitScope_Output,
                                AU_OUT_BUS,
                                &size,
                                nullptr);
  if (rv != noErr) {
    LOG("AudioUnitGetPropertyInfo/kAudioDevicePropertyPreferredChannelLayout rv=%d", rv);
    return CUBEB_LAYOUT_UNDEFINED;
  }
  assert(size > 0);

  auto layout = make_sized_audio_channel_layout(size);
  rv = AudioUnitGetProperty(output_unit,
                            kAudioDevicePropertyPreferredChannelLayout,
                            kAudioUnitScope_Output,
                            AU_OUT_BUS,
                            layout.get(),
                            &size);
  if (rv != noErr) {
    LOG("AudioUnitGetProperty/kAudioDevicePropertyPreferredChannelLayout rv=%d", rv);
    return CUBEB_LAYOUT_UNDEFINED;
  }

  return audiounit_convert_channel_layout(layout.get());
}

static cubeb_channel_layout
audiounit_get_current_channel_layout(AudioUnit output_unit)
{
  OSStatus rv = noErr;
  UInt32 size = 0;
  rv = AudioUnitGetPropertyInfo(output_unit,
                                kAudioUnitProperty_AudioChannelLayout,
                                kAudioUnitScope_Output,
                                AU_OUT_BUS,
                                &size,
                                nullptr);
  if (rv != noErr) {
    LOG("AudioUnitGetPropertyInfo/kAudioUnitProperty_AudioChannelLayout rv=%d", rv);
    // This property isn't known before macOS 10.12, attempt another method.
    return audiounit_get_preferred_channel_layout(output_unit);
  }
  assert(size > 0);

  auto layout = make_sized_audio_channel_layout(size);
  rv = AudioUnitGetProperty(output_unit,
                            kAudioUnitProperty_AudioChannelLayout,
                            kAudioUnitScope_Output,
                            AU_OUT_BUS,
                            layout.get(),
                            &size);
  if (rv != noErr) {
    LOG("AudioUnitGetProperty/kAudioUnitProperty_AudioChannelLayout rv=%d", rv);
    return CUBEB_LAYOUT_UNDEFINED;
  }

  return audiounit_convert_channel_layout(layout.get());
}

static int audiounit_create_unit(AudioUnit * unit, device_info * device);

static OSStatus audiounit_remove_device_listener(cubeb * context);

static void
audiounit_destroy(cubeb * ctx)
{
  {
    auto_lock lock(ctx->mutex);

    // Disabling this assert for bug 1083664 -- we seem to leak a stream
    // assert(ctx->active_streams == 0);
    if (audiounit_active_streams(ctx) > 0) {
      LOG("(%p) API misuse, %d streams active when context destroyed!", ctx, audiounit_active_streams(ctx));
    }

    /* Unregister the callback if necessary. */
    if (ctx->collection_changed_callback) {
      audiounit_remove_device_listener(ctx);
    }
  }

  delete ctx;
}

static void audiounit_stream_destroy(cubeb_stream * stm);

static int
audio_stream_desc_init(AudioStreamBasicDescription * ss,
                       const cubeb_stream_params * stream_params)
{
  switch (stream_params->format) {
  case CUBEB_SAMPLE_S16LE:
    ss->mBitsPerChannel = 16;
    ss->mFormatFlags = kAudioFormatFlagIsSignedInteger;
    break;
  case CUBEB_SAMPLE_S16BE:
    ss->mBitsPerChannel = 16;
    ss->mFormatFlags = kAudioFormatFlagIsSignedInteger |
      kAudioFormatFlagIsBigEndian;
    break;
  case CUBEB_SAMPLE_FLOAT32LE:
    ss->mBitsPerChannel = 32;
    ss->mFormatFlags = kAudioFormatFlagIsFloat;
    break;
  case CUBEB_SAMPLE_FLOAT32BE:
    ss->mBitsPerChannel = 32;
    ss->mFormatFlags = kAudioFormatFlagIsFloat |
      kAudioFormatFlagIsBigEndian;
    break;
  default:
    return CUBEB_ERROR_INVALID_FORMAT;
  }

  ss->mFormatID = kAudioFormatLinearPCM;
  ss->mFormatFlags |= kLinearPCMFormatFlagIsPacked;
  ss->mSampleRate = stream_params->rate;
  ss->mChannelsPerFrame = stream_params->channels;

  ss->mBytesPerFrame = (ss->mBitsPerChannel / 8) * ss->mChannelsPerFrame;
  ss->mFramesPerPacket = 1;
  ss->mBytesPerPacket = ss->mBytesPerFrame * ss->mFramesPerPacket;

  ss->mReserved = 0;

  return CUBEB_OK;
}

void
audiounit_init_mixer(cubeb_stream * stm)
{
  // We can't rely on macOS' AudioUnit to properly downmix (or upmix) the audio
  // data, it silently drop the channels so we need to remix the
  // audio data by ourselves to keep all the information.
  stm->mixer.reset(cubeb_mixer_create(stm->output_stream_params.format,
                                      stm->output_stream_params.channels,
                                      stm->output_stream_params.layout,
                                      stm->context->channels,
                                      stm->context->layout));
  assert(stm->mixer);
}

static int
audiounit_set_channel_layout(AudioUnit unit,
                             io_side side,
                             cubeb_channel_layout layout)
{
  if (side != io_side::OUTPUT) {
    return CUBEB_ERROR;
  }

  if (layout == CUBEB_LAYOUT_UNDEFINED) {
    // We leave everything as-is...
    return CUBEB_OK;
  }


  OSStatus r;
  uint32_t nb_channels = cubeb_channel_layout_nb_channels(layout);

  // We do not use CoreAudio standard layout for lack of documentation on what
  // the actual channel orders are. So we set a custom layout.
  size_t size = offsetof(AudioChannelLayout, mChannelDescriptions[nb_channels]);
  auto au_layout = make_sized_audio_channel_layout(size);
  au_layout->mChannelLayoutTag = kAudioChannelLayoutTag_UseChannelDescriptions;
  au_layout->mNumberChannelDescriptions = nb_channels;

  uint32_t channels = 0;
  cubeb_channel_layout channelMap = layout;
  for (uint32_t i = 0; channelMap != 0; ++i) {
    XASSERT(channels < nb_channels);
    uint32_t channel = (channelMap & 1) << i;
    if (channel != 0) {
      au_layout->mChannelDescriptions[channels].mChannelLabel =
        cubeb_channel_to_channel_label(static_cast<cubeb_channel>(channel));
      au_layout->mChannelDescriptions[channels].mChannelFlags = kAudioChannelFlags_AllOff;
      channels++;
    }
    channelMap = channelMap >> 1;
  }

  r = AudioUnitSetProperty(unit,
                           kAudioUnitProperty_AudioChannelLayout,
                           kAudioUnitScope_Input,
                           AU_OUT_BUS,
                           au_layout.get(),
                           size);
  if (r != noErr) {
    LOG("AudioUnitSetProperty/%s/kAudioUnitProperty_AudioChannelLayout rv=%d", to_string(side), r);
    return CUBEB_ERROR;
  }

  return CUBEB_OK;
}

void
audiounit_layout_init(cubeb_stream * stm, io_side side)
{
  // We currently don't support the input layout setting.
  if (side == io_side::INPUT) {
    return;
  }

  stm->context->layout = audiounit_get_current_channel_layout(stm->output_unit);

  audiounit_set_channel_layout(stm->output_unit, io_side::OUTPUT, stm->context->layout);
}

static vector<AudioObjectID>
audiounit_get_sub_devices(AudioDeviceID device_id)
{
  vector<AudioDeviceID> sub_devices;
  AudioObjectPropertyAddress property_address = { kAudioAggregateDevicePropertyActiveSubDeviceList,
                                                  kAudioObjectPropertyScopeGlobal,
                                                  kAudioObjectPropertyElementMaster };
  UInt32 size = 0;
  OSStatus rv = AudioObjectGetPropertyDataSize(device_id,
                                               &property_address,
                                               0,
                                               nullptr,
                                               &size);

  if (rv != noErr) {
    sub_devices.push_back(device_id);
    return sub_devices;
  }

  uint32_t count = static_cast<uint32_t>(size / sizeof(AudioObjectID));
  sub_devices.resize(count);
  rv = AudioObjectGetPropertyData(device_id,
                                  &property_address,
                                  0,
                                  nullptr,
                                  &size,
                                  sub_devices.data());
  if (rv != noErr) {
    sub_devices.clear();
    sub_devices.push_back(device_id);
  } else {
    LOG("Found %u sub-devices", count);
  }
  return sub_devices;
}

static int
audiounit_create_blank_aggregate_device(AudioObjectID * plugin_id, AudioDeviceID * aggregate_device_id)
{
  AudioObjectPropertyAddress address_plugin_bundle_id = { kAudioHardwarePropertyPlugInForBundleID,
                                                          kAudioObjectPropertyScopeGlobal,
                                                          kAudioObjectPropertyElementMaster };
  UInt32 size = 0;
  OSStatus r = AudioObjectGetPropertyDataSize(kAudioObjectSystemObject,
                                              &address_plugin_bundle_id,
                                              0, NULL,
                                              &size);
  if (r != noErr) {
    LOG("AudioHardwareGetPropertyInfo/kAudioHardwarePropertyPlugInForBundleID, rv=%d", r);
    return CUBEB_ERROR;
  }

  AudioValueTranslation translation_value;
  CFStringRef in_bundle_ref = CFSTR("com.apple.audio.CoreAudio");
  translation_value.mInputData = &in_bundle_ref;
  translation_value.mInputDataSize = sizeof(in_bundle_ref);
  translation_value.mOutputData = plugin_id;
  translation_value.mOutputDataSize = sizeof(*plugin_id);

  r = AudioObjectGetPropertyData(kAudioObjectSystemObject,
                                 &address_plugin_bundle_id,
                                 0,
                                 nullptr,
                                 &size,
                                 &translation_value);
  if (r != noErr) {
    LOG("AudioHardwareGetProperty/kAudioHardwarePropertyPlugInForBundleID, rv=%d", r);
    return CUBEB_ERROR;
  }

  AudioObjectPropertyAddress create_aggregate_device_address = { kAudioPlugInCreateAggregateDevice,
                                                                 kAudioObjectPropertyScopeGlobal,
                                                                 kAudioObjectPropertyElementMaster };
  r = AudioObjectGetPropertyDataSize(*plugin_id,
                                     &create_aggregate_device_address,
                                     0,
                                     nullptr,
                                     &size);
  if (r != noErr) {
    LOG("AudioObjectGetPropertyDataSize/kAudioPlugInCreateAggregateDevice, rv=%d", r);
    return CUBEB_ERROR;
  }

  CFMutableDictionaryRef aggregate_device_dict = CFDictionaryCreateMutable(kCFAllocatorDefault, 0,
                                                                           &kCFTypeDictionaryKeyCallBacks,
                                                                           &kCFTypeDictionaryValueCallBacks);
  struct timeval timestamp;
  gettimeofday(&timestamp, NULL);
  long long int time_id = timestamp.tv_sec * 1000000LL + timestamp.tv_usec;
  CFStringRef aggregate_device_name = CFStringCreateWithFormat(NULL, NULL, CFSTR("%s_%llx"), PRIVATE_AGGREGATE_DEVICE_NAME, time_id);
  CFDictionaryAddValue(aggregate_device_dict, CFSTR(kAudioAggregateDeviceNameKey), aggregate_device_name);
  CFRelease(aggregate_device_name);

  CFStringRef aggregate_device_UID = CFStringCreateWithFormat(NULL, NULL, CFSTR("org.mozilla.%s_%llx"), PRIVATE_AGGREGATE_DEVICE_NAME, time_id);
  CFDictionaryAddValue(aggregate_device_dict, CFSTR(kAudioAggregateDeviceUIDKey), aggregate_device_UID);
  CFRelease(aggregate_device_UID);

  int private_value = 1;
  CFNumberRef aggregate_device_private_key = CFNumberCreate(kCFAllocatorDefault, kCFNumberIntType, &private_value);
  CFDictionaryAddValue(aggregate_device_dict, CFSTR(kAudioAggregateDeviceIsPrivateKey), aggregate_device_private_key);
  CFRelease(aggregate_device_private_key);

  int stacked_value = 0;
  CFNumberRef aggregate_device_stacked_key = CFNumberCreate(kCFAllocatorDefault, kCFNumberIntType, &stacked_value);
  CFDictionaryAddValue(aggregate_device_dict, CFSTR(kAudioAggregateDeviceIsStackedKey), aggregate_device_stacked_key);
  CFRelease(aggregate_device_stacked_key);

  r = AudioObjectGetPropertyData(*plugin_id,
                                 &create_aggregate_device_address,
                                 sizeof(aggregate_device_dict),
                                 &aggregate_device_dict,
                                 &size,
                                 aggregate_device_id);
  CFRelease(aggregate_device_dict);
  if (r != noErr) {
    LOG("AudioObjectGetPropertyData/kAudioPlugInCreateAggregateDevice, rv=%d", r);
    return CUBEB_ERROR;
  }
  LOG("New aggregate device %u", *aggregate_device_id);

  return CUBEB_OK;
}

static CFStringRef
get_device_name(AudioDeviceID id)
{
  UInt32 size = sizeof(CFStringRef);
  CFStringRef UIname = nullptr;
  AudioObjectPropertyAddress address_uuid = { kAudioDevicePropertyDeviceUID,
                                              kAudioObjectPropertyScopeGlobal,
                                              kAudioObjectPropertyElementMaster };
  OSStatus err = AudioObjectGetPropertyData(id, &address_uuid, 0, nullptr, &size, &UIname);
  return (err == noErr) ? UIname : NULL;
}

static int
audiounit_set_aggregate_sub_device_list(AudioDeviceID aggregate_device_id,
                                        AudioDeviceID input_device_id,
                                        AudioDeviceID output_device_id)
{
  LOG("Add devices input %u and output %u into aggregate device %u",
      input_device_id, output_device_id, aggregate_device_id);
  const vector<AudioDeviceID> output_sub_devices = audiounit_get_sub_devices(output_device_id);
  const vector<AudioDeviceID> input_sub_devices = audiounit_get_sub_devices(input_device_id);

  CFMutableArrayRef aggregate_sub_devices_array = CFArrayCreateMutable(NULL, 0, &kCFTypeArrayCallBacks);
  /* The order of the items in the array is significant and is used to determine the order of the streams
     of the AudioAggregateDevice. */
  for (UInt32 i = 0; i < output_sub_devices.size(); i++) {
    CFStringRef ref = get_device_name(output_sub_devices[i]);
    if (ref == NULL) {
      CFRelease(aggregate_sub_devices_array);
      return CUBEB_ERROR;
    }
    CFArrayAppendValue(aggregate_sub_devices_array, ref);
  }
  for (UInt32 i = 0; i < input_sub_devices.size(); i++) {
    CFStringRef ref = get_device_name(input_sub_devices[i]);
    if (ref == NULL) {
      CFRelease(aggregate_sub_devices_array);
      return CUBEB_ERROR;
    }
    CFArrayAppendValue(aggregate_sub_devices_array, ref);
  }

  AudioObjectPropertyAddress aggregate_sub_device_list = { kAudioAggregateDevicePropertyFullSubDeviceList,
                                                           kAudioObjectPropertyScopeGlobal,
                                                           kAudioObjectPropertyElementMaster };
  UInt32 size = sizeof(CFMutableArrayRef);
  OSStatus rv = AudioObjectSetPropertyData(aggregate_device_id,
                                           &aggregate_sub_device_list,
                                           0,
                                           nullptr,
                                           size,
                                           &aggregate_sub_devices_array);
  CFRelease(aggregate_sub_devices_array);
  if (rv != noErr) {
    LOG("AudioObjectSetPropertyData/kAudioAggregateDevicePropertyFullSubDeviceList, rv=%d", rv);
    return CUBEB_ERROR;
  }

  return CUBEB_OK;
}

static int
audiounit_set_master_aggregate_device(const AudioDeviceID aggregate_device_id)
{
  assert(aggregate_device_id);
  AudioObjectPropertyAddress master_aggregate_sub_device =  { kAudioAggregateDevicePropertyMasterSubDevice,
                                                              kAudioObjectPropertyScopeGlobal,
                                                              kAudioObjectPropertyElementMaster };

  // Master become the 1st output sub device
  AudioDeviceID output_device_id = audiounit_get_default_device_id(CUBEB_DEVICE_TYPE_OUTPUT);
  const vector<AudioDeviceID> output_sub_devices = audiounit_get_sub_devices(output_device_id);
  CFStringRef master_sub_device = get_device_name(output_sub_devices[0]);

  UInt32 size = sizeof(CFStringRef);
  OSStatus rv = AudioObjectSetPropertyData(aggregate_device_id,
                                           &master_aggregate_sub_device,
                                           0,
                                           NULL,
                                           size,
                                           &master_sub_device);
  if (rv != noErr) {
    LOG("AudioObjectSetPropertyData/kAudioAggregateDevicePropertyMasterSubDevice, rv=%d", rv);
    return CUBEB_ERROR;
  }

  return CUBEB_OK;
}

static int
audiounit_activate_clock_drift_compensation(const AudioDeviceID aggregate_device_id)
{
  assert(aggregate_device_id);
  AudioObjectPropertyAddress address_owned = { kAudioObjectPropertyOwnedObjects,
                                               kAudioObjectPropertyScopeGlobal,
                                               kAudioObjectPropertyElementMaster };

  UInt32 qualifier_data_size = sizeof(AudioObjectID);
  AudioClassID class_id = kAudioSubDeviceClassID;
  void * qualifier_data = &class_id;
  UInt32 size = 0;
  OSStatus rv = AudioObjectGetPropertyDataSize(aggregate_device_id,
                                               &address_owned,
                                               qualifier_data_size,
                                               qualifier_data,
                                               &size);
  if (rv != noErr) {
    LOG("AudioObjectGetPropertyDataSize/kAudioObjectPropertyOwnedObjects, rv=%d", rv);
    return CUBEB_ERROR;
  }

  UInt32 subdevices_num = 0;
  subdevices_num = size / sizeof(AudioObjectID);
  AudioObjectID sub_devices[subdevices_num];
  size = sizeof(sub_devices);

  rv = AudioObjectGetPropertyData(aggregate_device_id,
                                  &address_owned,
                                  qualifier_data_size,
                                  qualifier_data,
                                  &size,
                                  sub_devices);
  if (rv != noErr) {
    LOG("AudioObjectGetPropertyData/kAudioObjectPropertyOwnedObjects, rv=%d", rv);
    return CUBEB_ERROR;
  }

  AudioObjectPropertyAddress address_drift = { kAudioSubDevicePropertyDriftCompensation,
                                               kAudioObjectPropertyScopeGlobal,
                                               kAudioObjectPropertyElementMaster };

  // Start from the second device since the first is the master clock
  for (UInt32 i = 1; i < subdevices_num; ++i) {
    UInt32 drift_compensation_value = 1;
    rv = AudioObjectSetPropertyData(sub_devices[i],
                                    &address_drift,
                                    0,
                                    nullptr,
                                    sizeof(UInt32),
                                    &drift_compensation_value);
    if (rv != noErr) {
      LOG("AudioObjectSetPropertyData/kAudioSubDevicePropertyDriftCompensation, rv=%d", rv);
      return CUBEB_OK;
    }
  }
  return CUBEB_OK;
}

static int audiounit_destroy_aggregate_device(AudioObjectID plugin_id, AudioDeviceID * aggregate_device_id);
static void audiounit_get_available_samplerate(AudioObjectID devid, AudioObjectPropertyScope scope,
                                   uint32_t * min, uint32_t * max, uint32_t * def);
static int
audiounit_create_device_from_hwdev(cubeb_device_info * dev_info, AudioObjectID devid, cubeb_device_type type);

static void
audiounit_workaround_for_airpod(cubeb_stream * stm)
{
  cubeb_device_info input_device_info;
  audiounit_create_device_from_hwdev(&input_device_info, stm->input_device.id, CUBEB_DEVICE_TYPE_INPUT);

  cubeb_device_info output_device_info;
  audiounit_create_device_from_hwdev(&output_device_info, stm->output_device.id, CUBEB_DEVICE_TYPE_OUTPUT);

  std::string input_name_str(input_device_info.friendly_name);
  std::string output_name_str(output_device_info.friendly_name);

  if( input_name_str.find("AirPods") != std::string::npos
    && output_name_str.find("AirPods") != std::string::npos ) {
    uint32_t input_min_rate = 0;
    uint32_t input_max_rate = 0;
    uint32_t input_nominal_rate = 0;
    audiounit_get_available_samplerate(stm->input_device.id, kAudioObjectPropertyScopeGlobal,
                                       &input_min_rate, &input_max_rate, &input_nominal_rate);
    LOG("(%p) Input device %u, name: %s, min: %u, max: %u, nominal rate: %u", stm, stm->input_device.id
    , input_device_info.friendly_name, input_min_rate, input_max_rate, input_nominal_rate);
    uint32_t output_min_rate = 0;
    uint32_t output_max_rate = 0;
    uint32_t output_nominal_rate = 0;
    audiounit_get_available_samplerate(stm->output_device.id, kAudioObjectPropertyScopeGlobal,
                                       &output_min_rate, &output_max_rate, &output_nominal_rate);
    LOG("(%p) Output device %u, name: %s, min: %u, max: %u, nominal rate: %u", stm, stm->output_device.id
    , output_device_info.friendly_name, output_min_rate, output_max_rate, output_nominal_rate);

    Float64 rate = input_nominal_rate;
    AudioObjectPropertyAddress addr = {kAudioDevicePropertyNominalSampleRate,
                                       kAudioObjectPropertyScopeGlobal,
                                       kAudioObjectPropertyElementMaster};

    OSStatus rv = AudioObjectSetPropertyData(stm->aggregate_device_id,
                                             &addr,
                                             0,
                                             nullptr,
                                             sizeof(Float64),
                                             &rate);
    if (rv != noErr) {
      LOG("Non fatal error, AudioObjectSetPropertyData/kAudioDevicePropertyNominalSampleRate, rv=%d", rv);
    }
  }
}

/*
 * Aggregate Device is a virtual audio interface which utilizes inputs and outputs
 * of one or more physical audio interfaces. It is possible to use the clock of
 * one of the devices as a master clock for all the combined devices and enable
 * drift compensation for the devices that are not designated clock master.
 *
 * Creating a new aggregate device programmatically requires [0][1]:
 * 1. Locate the base plug-in ("com.apple.audio.CoreAudio")
 * 2. Create a dictionary that describes the aggregate device
 *    (don't add sub-devices in that step, prone to fail [0])
 * 3. Ask the base plug-in to create the aggregate device (blank)
 * 4. Add the array of sub-devices.
 * 5. Set the master device (1st output device in our case)
 * 6. Enable drift compensation for the non-master devices
 *
 * [0] https://lists.apple.com/archives/coreaudio-api/2006/Apr/msg00092.html
 * [1] https://lists.apple.com/archives/coreaudio-api/2005/Jul/msg00150.html
 * [2] CoreAudio.framework/Headers/AudioHardware.h
 * */
static int
audiounit_create_aggregate_device(cubeb_stream * stm)
{
  int r = audiounit_create_blank_aggregate_device(&stm->plugin_id, &stm->aggregate_device_id);
  if (r != CUBEB_OK) {
    LOG("(%p) Failed to create blank aggregate device", stm);
    return CUBEB_ERROR;
  }

  r = audiounit_set_aggregate_sub_device_list(stm->aggregate_device_id, stm->input_device.id, stm->output_device.id);
  if (r != CUBEB_OK) {
    LOG("(%p) Failed to set aggregate sub-device list", stm);
    audiounit_destroy_aggregate_device(stm->plugin_id, &stm->aggregate_device_id);
    return CUBEB_ERROR;
  }

  r = audiounit_set_master_aggregate_device(stm->aggregate_device_id);
  if (r != CUBEB_OK) {
    LOG("(%p) Failed to set master sub-device for aggregate device", stm);
    audiounit_destroy_aggregate_device(stm->plugin_id, &stm->aggregate_device_id);
    return  CUBEB_ERROR;
  }

  r = audiounit_activate_clock_drift_compensation(stm->aggregate_device_id);
  if (r != CUBEB_OK) {
    LOG("(%p) Failed to activate clock drift compensation for aggregate device", stm);
    audiounit_destroy_aggregate_device(stm->plugin_id, &stm->aggregate_device_id);
    return  CUBEB_ERROR;
  }

  audiounit_workaround_for_airpod(stm);

  return CUBEB_OK;
}

static int
audiounit_destroy_aggregate_device(AudioObjectID plugin_id, AudioDeviceID * aggregate_device_id)
{
  assert(aggregate_device_id &&
         *aggregate_device_id != kAudioDeviceUnknown &&
         plugin_id != kAudioObjectUnknown);
  AudioObjectPropertyAddress destroy_aggregate_device_addr = { kAudioPlugInDestroyAggregateDevice,
                                                               kAudioObjectPropertyScopeGlobal,
                                                               kAudioObjectPropertyElementMaster};
  UInt32 size;
  OSStatus rv = AudioObjectGetPropertyDataSize(plugin_id,
                                               &destroy_aggregate_device_addr,
                                               0,
                                               NULL,
                                               &size);
  if (rv != noErr) {
    LOG("AudioObjectGetPropertyDataSize/kAudioPlugInDestroyAggregateDevice, rv=%d", rv);
    return CUBEB_ERROR;
  }

  rv = AudioObjectGetPropertyData(plugin_id,
                                  &destroy_aggregate_device_addr,
                                  0,
                                  NULL,
                                  &size,
                                  aggregate_device_id);
  if (rv != noErr) {
    LOG("AudioObjectGetPropertyData/kAudioPlugInDestroyAggregateDevice, rv=%d", rv);
    return CUBEB_ERROR;
  }

  LOG("Destroyed aggregate device %d", *aggregate_device_id);
  *aggregate_device_id = 0;
  return CUBEB_OK;
}

static int
audiounit_new_unit_instance(AudioUnit * unit, device_info * device)
{
  AudioComponentDescription desc;
  AudioComponent comp;
  OSStatus rv;

  desc.componentType = kAudioUnitType_Output;
#if TARGET_OS_IPHONE
  desc.componentSubType = kAudioUnitSubType_RemoteIO;
#else
  // Use the DefaultOutputUnit for output when no device is specified
  // so we retain automatic output device switching when the default
  // changes.  Once we have complete support for device notifications
  // and switching, we can use the AUHAL for everything.
  if ((device->flags & DEV_SYSTEM_DEFAULT)
      && (device->flags & DEV_OUTPUT)) {
    desc.componentSubType = kAudioUnitSubType_DefaultOutput;
  } else {
    desc.componentSubType = kAudioUnitSubType_HALOutput;
  }
#endif
  desc.componentManufacturer = kAudioUnitManufacturer_Apple;
  desc.componentFlags = 0;
  desc.componentFlagsMask = 0;
  comp = AudioComponentFindNext(NULL, &desc);
  if (comp == NULL) {
    LOG("Could not find matching audio hardware.");
    return CUBEB_ERROR;
  }

  rv = AudioComponentInstanceNew(comp, unit);
  if (rv != noErr) {
    LOG("AudioComponentInstanceNew rv=%d", rv);
    return CUBEB_ERROR;
  }
  return CUBEB_OK;
}

enum enable_state {
  DISABLE,
  ENABLE,
};

static int
audiounit_enable_unit_scope(AudioUnit * unit, io_side side, enable_state state)
{
  OSStatus rv;
  UInt32 enable = state;
  rv = AudioUnitSetProperty(*unit, kAudioOutputUnitProperty_EnableIO,
                            (side == io_side::INPUT) ? kAudioUnitScope_Input : kAudioUnitScope_Output,
                            (side == io_side::INPUT) ? AU_IN_BUS : AU_OUT_BUS,
                            &enable,
                            sizeof(UInt32));
  if (rv != noErr) {
    LOG("AudioUnitSetProperty/kAudioOutputUnitProperty_EnableIO rv=%d", rv);
    return CUBEB_ERROR;
  }
  return CUBEB_OK;
}

static int
audiounit_create_unit(AudioUnit * unit, device_info * device)
{
  assert(*unit == nullptr);
  assert(device);

  OSStatus rv;
  int r;

  r = audiounit_new_unit_instance(unit, device);
  if (r != CUBEB_OK) {
    return r;
  }
  assert(*unit);

  if ((device->flags & DEV_SYSTEM_DEFAULT)
      && (device->flags & DEV_OUTPUT)) {
    return CUBEB_OK;
  }


  if (device->flags & DEV_INPUT) {
    r = audiounit_enable_unit_scope(unit, io_side::INPUT, ENABLE);
    if (r != CUBEB_OK) {
      LOG("Failed to enable audiounit input scope ");
      return r;
    }
    r = audiounit_enable_unit_scope(unit, io_side::OUTPUT, DISABLE);
    if (r != CUBEB_OK) {
      LOG("Failed to disable audiounit output scope ");
      return r;
    }
  } else if (device->flags & DEV_OUTPUT) {
    r = audiounit_enable_unit_scope(unit, io_side::OUTPUT, ENABLE);
    if (r != CUBEB_OK) {
      LOG("Failed to enable audiounit output scope ");
      return r;
    }
    r = audiounit_enable_unit_scope(unit, io_side::INPUT, DISABLE);
    if (r != CUBEB_OK) {
      LOG("Failed to disable audiounit input scope ");
      return r;
    }
  } else {
    assert(false);
  }

  rv = AudioUnitSetProperty(*unit,
                            kAudioOutputUnitProperty_CurrentDevice,
                            kAudioUnitScope_Global,
                            0,
                            &device->id, sizeof(AudioDeviceID));
  if (rv != noErr) {
    LOG("AudioUnitSetProperty/kAudioOutputUnitProperty_CurrentDevice rv=%d", rv);
    return CUBEB_ERROR;
  }

  return CUBEB_OK;
}

static int
audiounit_init_input_linear_buffer(cubeb_stream * stream, uint32_t capacity)
{
  uint32_t size = capacity * stream->latency_frames * stream->input_desc.mChannelsPerFrame;
  if (stream->input_desc.mFormatFlags & kAudioFormatFlagIsSignedInteger) {
    stream->input_linear_buffer.reset(new auto_array_wrapper_impl<short>(size));
  } else {
    stream->input_linear_buffer.reset(new auto_array_wrapper_impl<float>(size));
  }
  assert(stream->input_linear_buffer->length() == 0);

  return CUBEB_OK;
}

static uint32_t
audiounit_clamp_latency(cubeb_stream * stm, uint32_t latency_frames)
{
  // For the 1st stream set anything within safe min-max
  assert(audiounit_active_streams(stm->context) > 0);
  if (audiounit_active_streams(stm->context) == 1) {
    return max(min<uint32_t>(latency_frames, SAFE_MAX_LATENCY_FRAMES),
                    SAFE_MIN_LATENCY_FRAMES);
  }
  assert(stm->output_unit);

  // If more than one stream operates in parallel
  // allow only lower values of latency
  int r;
  UInt32 output_buffer_size = 0;
  UInt32 size = sizeof(output_buffer_size);
  if (stm->output_unit) {
    r = AudioUnitGetProperty(stm->output_unit,
                            kAudioDevicePropertyBufferFrameSize,
                            kAudioUnitScope_Output,
                            AU_OUT_BUS,
                            &output_buffer_size,
                            &size);
    if (r != noErr) {
      LOG("AudioUnitGetProperty/output/kAudioDevicePropertyBufferFrameSize rv=%d", r);
      return 0;
    }

    output_buffer_size = max(min<uint32_t>(output_buffer_size, SAFE_MAX_LATENCY_FRAMES),
                                  SAFE_MIN_LATENCY_FRAMES);
  }

  UInt32 input_buffer_size = 0;
  if (stm->input_unit) {
    r = AudioUnitGetProperty(stm->input_unit,
                            kAudioDevicePropertyBufferFrameSize,
                            kAudioUnitScope_Input,
                            AU_IN_BUS,
                            &input_buffer_size,
                            &size);
    if (r != noErr) {
      LOG("AudioUnitGetProperty/input/kAudioDevicePropertyBufferFrameSize rv=%d", r);
      return 0;
    }

    input_buffer_size = max(min<uint32_t>(input_buffer_size, SAFE_MAX_LATENCY_FRAMES),
                                 SAFE_MIN_LATENCY_FRAMES);
  }

  // Every following active streams can only set smaller latency
  UInt32 upper_latency_limit = 0;
  if (input_buffer_size != 0 && output_buffer_size != 0) {
    upper_latency_limit = min<uint32_t>(input_buffer_size, output_buffer_size);
  } else if (input_buffer_size != 0) {
    upper_latency_limit = input_buffer_size;
  } else if (output_buffer_size != 0) {
    upper_latency_limit = output_buffer_size;
  } else {
    upper_latency_limit = SAFE_MAX_LATENCY_FRAMES;
  }

  return max(min<uint32_t>(latency_frames, upper_latency_limit),
                  SAFE_MIN_LATENCY_FRAMES);
}

/*
 * Change buffer size is prone to deadlock thus we change it
 * following the steps:
 * - register a listener for the buffer size property
 * - change the property
 * - wait until the listener is executed
 * - property has changed, remove the listener
 * */
static void
buffer_size_changed_callback(void * inClientData,
                             AudioUnit inUnit,
                             AudioUnitPropertyID inPropertyID,
                             AudioUnitScope inScope,
                             AudioUnitElement inElement)
{
  cubeb_stream * stm = (cubeb_stream *)inClientData;

  AudioUnit au = inUnit;
  AudioUnitScope au_scope = kAudioUnitScope_Input;
  AudioUnitElement au_element = inElement;
  char const * au_type = "output";

  if (AU_IN_BUS == inElement) {
    au_scope = kAudioUnitScope_Output;
    au_type = "input";
  }

  switch (inPropertyID) {

    case kAudioDevicePropertyBufferFrameSize: {
      if (inScope != au_scope) {
        break;
      }
      UInt32 new_buffer_size;
      UInt32 outSize = sizeof(UInt32);
      OSStatus r = AudioUnitGetProperty(au,
                                        kAudioDevicePropertyBufferFrameSize,
                                        au_scope,
                                        au_element,
                                        &new_buffer_size,
                                        &outSize);
      if (r != noErr) {
        LOG("(%p) Event: kAudioDevicePropertyBufferFrameSize: Cannot get current buffer size", stm);
      } else {
        LOG("(%p) Event: kAudioDevicePropertyBufferFrameSize: New %s buffer size = %d for scope %d", stm,
            au_type, new_buffer_size, inScope);
      }
      stm->buffer_size_change_state = true;
      break;
    }
  }
}

static int
audiounit_set_buffer_size(cubeb_stream * stm, uint32_t new_size_frames, io_side side)
{
  AudioUnit au = stm->output_unit;
  AudioUnitScope au_scope = kAudioUnitScope_Input;
  AudioUnitElement au_element = AU_OUT_BUS;

  if (side == io_side::INPUT) {
    au = stm->input_unit;
    au_scope = kAudioUnitScope_Output;
    au_element = AU_IN_BUS;
  }

  uint32_t buffer_frames = 0;
  UInt32 size = sizeof(buffer_frames);
  int r = AudioUnitGetProperty(au,
                               kAudioDevicePropertyBufferFrameSize,
                               au_scope,
                               au_element,
                               &buffer_frames,
                               &size);
  if (r != noErr) {
    LOG("AudioUnitGetProperty/%s/kAudioDevicePropertyBufferFrameSize rv=%d", to_string(side), r);
    return CUBEB_ERROR;
  }

  if (new_size_frames == buffer_frames) {
    LOG("(%p) No need to update %s buffer size already %u frames", stm, to_string(side), buffer_frames);
    return CUBEB_OK;
  }

  r = AudioUnitAddPropertyListener(au,
                                   kAudioDevicePropertyBufferFrameSize,
                                   buffer_size_changed_callback,
                                   stm);
  if (r != noErr) {
    LOG("AudioUnitAddPropertyListener/%s/kAudioDevicePropertyBufferFrameSize rv=%d", to_string(side), r);
    return CUBEB_ERROR;
  }

  stm->buffer_size_change_state = false;

  r = AudioUnitSetProperty(au,
                           kAudioDevicePropertyBufferFrameSize,
                           au_scope,
                           au_element,
                           &new_size_frames,
                           sizeof(new_size_frames));
  if (r != noErr) {
    LOG("AudioUnitSetProperty/%s/kAudioDevicePropertyBufferFrameSize rv=%d", to_string(side), r);

    r = AudioUnitRemovePropertyListenerWithUserData(au,
                                                    kAudioDevicePropertyBufferFrameSize,
                                                    buffer_size_changed_callback,
                                                    stm);
    if (r != noErr) {
      LOG("AudioUnitAddPropertyListener/%s/kAudioDevicePropertyBufferFrameSize rv=%d", to_string(side), r);
    }

    return CUBEB_ERROR;
  }

  int count = 0;
  while (!stm->buffer_size_change_state && count++ < 30) {
    struct timespec req, rem;
    req.tv_sec = 0;
    req.tv_nsec = 100000000L; // 0.1 sec
    if (nanosleep(&req , &rem) < 0 ) {
      LOG("(%p) Warning: nanosleep call failed or interrupted. Remaining time %ld nano secs \n", stm, rem.tv_nsec);
    }
    LOG("(%p) audiounit_set_buffer_size : wait count = %d", stm, count);
  }

  r = AudioUnitRemovePropertyListenerWithUserData(au,
                                                  kAudioDevicePropertyBufferFrameSize,
                                                  buffer_size_changed_callback,
                                                  stm);
  if (r != noErr) {
    LOG("AudioUnitAddPropertyListener/%s/kAudioDevicePropertyBufferFrameSize rv=%d", to_string(side), r);
    return CUBEB_ERROR;
  }

  if (!stm->buffer_size_change_state && count >= 30) {
    LOG("(%p) Error, did not get buffer size change callback ...", stm);
    return CUBEB_ERROR;
  }

  LOG("(%p) %s buffer size changed to %u frames.", stm, to_string(side), new_size_frames);
  return CUBEB_OK;
}

static int
audiounit_configure_input(cubeb_stream * stm)
{
  assert(stm && stm->input_unit);

  int r = 0;
  UInt32 size;
  AURenderCallbackStruct aurcbs_in;

  LOG("(%p) Opening input side: rate %u, channels %u, format %d, latency in frames %u.",
      stm, stm->input_stream_params.rate, stm->input_stream_params.channels,
      stm->input_stream_params.format, stm->latency_frames);

  /* Get input device sample rate. */
  AudioStreamBasicDescription input_hw_desc;
  size = sizeof(AudioStreamBasicDescription);
  r = AudioUnitGetProperty(stm->input_unit,
                           kAudioUnitProperty_StreamFormat,
                           kAudioUnitScope_Input,
                           AU_IN_BUS,
                           &input_hw_desc,
                           &size);
  if (r != noErr) {
    LOG("AudioUnitGetProperty/input/kAudioUnitProperty_StreamFormat rv=%d", r);
    return CUBEB_ERROR;
  }
  stm->input_hw_rate = input_hw_desc.mSampleRate;
  LOG("(%p) Input device sampling rate: %.2f", stm, stm->input_hw_rate);

  /* Set format description according to the input params. */
  r = audio_stream_desc_init(&stm->input_desc, &stm->input_stream_params);
  if (r != CUBEB_OK) {
    LOG("(%p) Setting format description for input failed.", stm);
    return r;
  }

  // Use latency to set buffer size
  r = audiounit_set_buffer_size(stm, stm->latency_frames, io_side::INPUT);
  if (r != CUBEB_OK) {
    LOG("(%p) Error in change input buffer size.", stm);
    return CUBEB_ERROR;
  }

  AudioStreamBasicDescription src_desc = stm->input_desc;
  /* Input AudioUnit must be configured with device's sample rate.
     we will resample inside input callback. */
  src_desc.mSampleRate = stm->input_hw_rate;

  r = AudioUnitSetProperty(stm->input_unit,
                           kAudioUnitProperty_StreamFormat,
                           kAudioUnitScope_Output,
                           AU_IN_BUS,
                           &src_desc,
                           sizeof(AudioStreamBasicDescription));
  if (r != noErr) {
    LOG("AudioUnitSetProperty/input/kAudioUnitProperty_StreamFormat rv=%d", r);
    return CUBEB_ERROR;
  }

  /* Frames per buffer in the input callback. */
  r = AudioUnitSetProperty(stm->input_unit,
                           kAudioUnitProperty_MaximumFramesPerSlice,
                           kAudioUnitScope_Global,
                           AU_IN_BUS,
                           &stm->latency_frames,
                           sizeof(UInt32));
  if (r != noErr) {
    LOG("AudioUnitSetProperty/input/kAudioUnitProperty_MaximumFramesPerSlice rv=%d", r);
    return CUBEB_ERROR;
  }

  // Input only capacity
  unsigned int array_capacity = 1;
  if (has_output(stm)) {
    // Full-duplex increase capacity
    array_capacity = 8;
  }
  if (audiounit_init_input_linear_buffer(stm, array_capacity) != CUBEB_OK) {
    return CUBEB_ERROR;
  }

  aurcbs_in.inputProc = audiounit_input_callback;
  aurcbs_in.inputProcRefCon = stm;

  r = AudioUnitSetProperty(stm->input_unit,
                           kAudioOutputUnitProperty_SetInputCallback,
                           kAudioUnitScope_Global,
                           AU_OUT_BUS,
                           &aurcbs_in,
                           sizeof(aurcbs_in));
  if (r != noErr) {
    LOG("AudioUnitSetProperty/input/kAudioOutputUnitProperty_SetInputCallback rv=%d", r);
    return CUBEB_ERROR;
  }

  stm->frames_read = 0;

  LOG("(%p) Input audiounit init successfully.", stm);

  return CUBEB_OK;
}

static int
audiounit_configure_output(cubeb_stream * stm)
{
  assert(stm && stm->output_unit);

  int r;
  AURenderCallbackStruct aurcbs_out;
  UInt32 size;


  LOG("(%p) Opening output side: rate %u, channels %u, format %d, latency in frames %u.",
      stm, stm->output_stream_params.rate, stm->output_stream_params.channels,
      stm->output_stream_params.format, stm->latency_frames);

  r = audio_stream_desc_init(&stm->output_desc, &stm->output_stream_params);
  if (r != CUBEB_OK) {
    LOG("(%p) Could not initialize the audio stream description.", stm);
    return r;
  }

  /* Get output device sample rate. */
  AudioStreamBasicDescription output_hw_desc;
  size = sizeof(AudioStreamBasicDescription);
  memset(&output_hw_desc, 0, size);
  r = AudioUnitGetProperty(stm->output_unit,
                           kAudioUnitProperty_StreamFormat,
                           kAudioUnitScope_Output,
                           AU_OUT_BUS,
                           &output_hw_desc,
                           &size);
  if (r != noErr) {
    LOG("AudioUnitGetProperty/output/kAudioUnitProperty_StreamFormat rv=%d", r);
    return CUBEB_ERROR;
  }
  stm->output_hw_rate = output_hw_desc.mSampleRate;
  LOG("(%p) Output device sampling rate: %.2f", stm, output_hw_desc.mSampleRate);
  stm->context->channels = output_hw_desc.mChannelsPerFrame;

  // Set the input layout to match the output device layout.
  audiounit_layout_init(stm, io_side::OUTPUT);
  if (stm->context->channels != stm->output_stream_params.channels ||
      stm->context->layout != stm->output_stream_params.layout) {
    LOG("Incompatible channel layouts detected, setting up remixer");
    audiounit_init_mixer(stm);
    // We will be remixing the data before it reaches the output device.
    // We need to adjust the number of channels and other
    // AudioStreamDescription details.
    stm->output_desc.mChannelsPerFrame = stm->context->channels;
    stm->output_desc.mBytesPerFrame = (stm->output_desc.mBitsPerChannel / 8) *
                                      stm->output_desc.mChannelsPerFrame;
    stm->output_desc.mBytesPerPacket =
      stm->output_desc.mBytesPerFrame * stm->output_desc.mFramesPerPacket;
  } else {
    stm->mixer = nullptr;
  }

  r = AudioUnitSetProperty(stm->output_unit,
                           kAudioUnitProperty_StreamFormat,
                           kAudioUnitScope_Input,
                           AU_OUT_BUS,
                           &stm->output_desc,
                           sizeof(AudioStreamBasicDescription));
  if (r != noErr) {
    LOG("AudioUnitSetProperty/output/kAudioUnitProperty_StreamFormat rv=%d", r);
    return CUBEB_ERROR;
  }

  r = audiounit_set_buffer_size(stm, stm->latency_frames, io_side::OUTPUT);
  if (r != CUBEB_OK) {
    LOG("(%p) Error in change output buffer size.", stm);
    return CUBEB_ERROR;
  }

  /* Frames per buffer in the input callback. */
  r = AudioUnitSetProperty(stm->output_unit,
                           kAudioUnitProperty_MaximumFramesPerSlice,
                           kAudioUnitScope_Global,
                           AU_OUT_BUS,
                           &stm->latency_frames,
                           sizeof(UInt32));
  if (r != noErr) {
    LOG("AudioUnitSetProperty/output/kAudioUnitProperty_MaximumFramesPerSlice rv=%d", r);
    return CUBEB_ERROR;
  }

  aurcbs_out.inputProc = audiounit_output_callback;
  aurcbs_out.inputProcRefCon = stm;
  r = AudioUnitSetProperty(stm->output_unit,
                           kAudioUnitProperty_SetRenderCallback,
                           kAudioUnitScope_Global,
                           AU_OUT_BUS,
                           &aurcbs_out,
                           sizeof(aurcbs_out));
  if (r != noErr) {
    LOG("AudioUnitSetProperty/output/kAudioUnitProperty_SetRenderCallback rv=%d", r);
    return CUBEB_ERROR;
  }

  stm->frames_written = 0;

  LOG("(%p) Output audiounit init successfully.", stm);
  return CUBEB_OK;
}

static int
audiounit_setup_stream(cubeb_stream * stm)
{
  stm->mutex.assert_current_thread_owns();

  if ((stm->input_stream_params.prefs & CUBEB_STREAM_PREF_LOOPBACK) ||
      (stm->output_stream_params.prefs & CUBEB_STREAM_PREF_LOOPBACK)) {
    LOG("(%p) Loopback not supported for audiounit.", stm);
    return CUBEB_ERROR_NOT_SUPPORTED;
  }

  int r = 0;

  device_info in_dev_info = stm->input_device;
  device_info out_dev_info = stm->output_device;

  if (has_input(stm) && has_output(stm) &&
      stm->input_device.id != stm->output_device.id) {
    r = audiounit_create_aggregate_device(stm);
    if (r != CUBEB_OK) {
      stm->aggregate_device_id = 0;
      LOG("(%p) Create aggregate devices failed.", stm);
      // !!!NOTE: It is not necessary to return here. If it does not
      // return it will fallback to the old implementation. The intention
      // is to investigate how often it fails. I plan to remove
      // it after a couple of weeks.
      return r;
    } else {
      in_dev_info.id = out_dev_info.id = stm->aggregate_device_id;
      in_dev_info.flags = DEV_INPUT;
      out_dev_info.flags = DEV_OUTPUT;
    }
  }

  if (has_input(stm)) {
    r = audiounit_create_unit(&stm->input_unit, &in_dev_info);
    if (r != CUBEB_OK) {
      LOG("(%p) AudioUnit creation for input failed.", stm);
      return r;
    }
  }

  if (has_output(stm)) {
    r = audiounit_create_unit(&stm->output_unit, &out_dev_info);
    if (r != CUBEB_OK) {
      LOG("(%p) AudioUnit creation for output failed.", stm);
      return r;
    }
  }

  /* Latency cannot change if another stream is operating in parallel. In this case
  * latecy is set to the other stream value. */
  if (audiounit_active_streams(stm->context) > 1) {
    LOG("(%p) More than one active stream, use global latency.", stm);
    stm->latency_frames = stm->context->global_latency_frames;
  } else {
    /* Silently clamp the latency down to the platform default, because we
    * synthetize the clock from the callbacks, and we want the clock to update
    * often. */
    stm->latency_frames = audiounit_clamp_latency(stm, stm->latency_frames);
    assert(stm->latency_frames); // Ungly error check
    audiounit_set_global_latency(stm->context, stm->latency_frames);
  }

  /* Configure I/O stream */
  if (has_input(stm)) {
    r = audiounit_configure_input(stm);
    if (r != CUBEB_OK) {
      LOG("(%p) Configure audiounit input failed.", stm);
      return r;
    }
  }

  if (has_output(stm)) {
    r = audiounit_configure_output(stm);
    if (r != CUBEB_OK) {
      LOG("(%p) Configure audiounit output failed.", stm);
      return r;
    }
  }

  // Setting the latency doesn't work well for USB headsets (eg. plantronics).
  // Keep the default latency for now.
#if 0
  buffer_size = latency;

  /* Get the range of latency this particular device can work with, and clamp
   * the requested latency to this acceptable range. */
#if !TARGET_OS_IPHONE
  if (audiounit_get_acceptable_latency_range(&latency_range) != CUBEB_OK) {
    return CUBEB_ERROR;
  }

  if (buffer_size < (unsigned int) latency_range.mMinimum) {
    buffer_size = (unsigned int) latency_range.mMinimum;
  } else if (buffer_size > (unsigned int) latency_range.mMaximum) {
    buffer_size = (unsigned int) latency_range.mMaximum;
  }

  /**
   * Get the default buffer size. If our latency request is below the default,
   * set it. Otherwise, use the default latency.
   **/
  size = sizeof(default_buffer_size);
  if (AudioUnitGetProperty(stm->output_unit, kAudioDevicePropertyBufferFrameSize,
        kAudioUnitScope_Output, 0, &default_buffer_size, &size) != 0) {
    return CUBEB_ERROR;
  }

  if (buffer_size < default_buffer_size) {
    /* Set the maximum number of frame that the render callback will ask for,
     * effectively setting the latency of the stream. This is process-wide. */
    if (AudioUnitSetProperty(stm->output_unit, kAudioDevicePropertyBufferFrameSize,
          kAudioUnitScope_Output, 0, &buffer_size, sizeof(buffer_size)) != 0) {
      return CUBEB_ERROR;
    }
  }
#else  // TARGET_OS_IPHONE
  //TODO: [[AVAudioSession sharedInstance] inputLatency]
  // http://stackoverflow.com/questions/13157523/kaudiodevicepropertybufferframesize-replacement-for-ios
#endif
#endif

  /* We use a resampler because input AudioUnit operates
   * reliable only in the capture device sample rate.
   * Resampler will convert it to the user sample rate
   * and deliver it to the callback. */
  uint32_t target_sample_rate;
  if (has_input(stm)) {
    target_sample_rate = stm->input_stream_params.rate;
  } else {
    assert(has_output(stm));
    target_sample_rate = stm->output_stream_params.rate;
  }

  cubeb_stream_params input_unconverted_params;
  if (has_input(stm)) {
    input_unconverted_params = stm->input_stream_params;
    /* Use the rate of the input device. */
    input_unconverted_params.rate = stm->input_hw_rate;
  }

  /* Create resampler. Output params are unchanged
   * because we do not need conversion on the output. */
  stm->resampler.reset(cubeb_resampler_create(stm,
                                              has_input(stm) ? &input_unconverted_params : NULL,
                                              has_output(stm) ? &stm->output_stream_params : NULL,
                                              target_sample_rate,
                                              stm->data_callback,
                                              stm->user_ptr,
                                              CUBEB_RESAMPLER_QUALITY_DESKTOP));
  if (!stm->resampler) {
    LOG("(%p) Could not create resampler.", stm);
    return CUBEB_ERROR;
  }

  if (stm->input_unit != NULL) {
    r = AudioUnitInitialize(stm->input_unit);
    if (r != noErr) {
      LOG("AudioUnitInitialize/input rv=%d", r);
      return CUBEB_ERROR;
    }
  }

  if (stm->output_unit != NULL) {
    r = AudioUnitInitialize(stm->output_unit);
    if (r != noErr) {
      LOG("AudioUnitInitialize/output rv=%d", r);
      return CUBEB_ERROR;
    }

    stm->current_latency_frames = audiounit_get_device_presentation_latency(stm->output_device.id, kAudioDevicePropertyScopeOutput);

    Float64 unit_s;
    UInt32 size = sizeof(unit_s);
    if (AudioUnitGetProperty(stm->output_unit, kAudioUnitProperty_Latency, kAudioUnitScope_Global, 0, &unit_s, &size) == noErr) {
      stm->current_latency_frames += static_cast<uint32_t>(unit_s * stm->output_desc.mSampleRate);
    }
  }

  if (stm->input_unit && stm->output_unit) {
    // According to the I/O hardware rate it is expected a specific pattern of callbacks
    // for example is input is 44100 and output is 48000 we expected no more than 2
    // out callback in a row.
    stm->expected_output_callbacks_in_a_row = ceilf(stm->output_hw_rate / stm->input_hw_rate);
  }

  r = audiounit_install_device_changed_callback(stm);
  if (r != CUBEB_OK) {
    LOG("(%p) Could not install all device change callback.", stm);
  }


  return CUBEB_OK;
}

cubeb_stream::cubeb_stream(cubeb * context)
  : context(context)
  , resampler(nullptr, cubeb_resampler_destroy)
  , mixer(nullptr, cubeb_mixer_destroy)
{
  PodZero(&input_desc, 1);
  PodZero(&output_desc, 1);
}

static void audiounit_stream_destroy_internal(cubeb_stream * stm);

static int
audiounit_stream_init(cubeb * context,
                      cubeb_stream ** stream,
                      char const * /* stream_name */,
                      cubeb_devid input_device,
                      cubeb_stream_params * input_stream_params,
                      cubeb_devid output_device,
                      cubeb_stream_params * output_stream_params,
                      unsigned int latency_frames,
                      cubeb_data_callback data_callback,
                      cubeb_state_callback state_callback,
                      void * user_ptr)
{
  assert(context);
  auto_lock context_lock(context->mutex);
  audiounit_increment_active_streams(context);
  unique_ptr<cubeb_stream, decltype(&audiounit_stream_destroy)> stm(new cubeb_stream(context),
                                                                    audiounit_stream_destroy_internal);
  int r;
  *stream = NULL;
  assert(latency_frames > 0);

  /* These could be different in the future if we have both
   * full-duplex stream and different devices for input vs output. */
  stm->data_callback = data_callback;
  stm->state_callback = state_callback;
  stm->user_ptr = user_ptr;
  stm->latency_frames = latency_frames;

  if ((input_device && !input_stream_params) ||
      (output_device && !output_stream_params)) {
    return CUBEB_ERROR_INVALID_PARAMETER;
  }
  if (input_stream_params) {
    stm->input_stream_params = *input_stream_params;
    r = audiounit_set_device_info(stm.get(), reinterpret_cast<uintptr_t>(input_device), io_side::INPUT);
    if (r != CUBEB_OK) {
      LOG("(%p) Fail to set device info for input.", stm.get());
      return r;
    }
  }
  if (output_stream_params) {
    stm->output_stream_params = *output_stream_params;
    r = audiounit_set_device_info(stm.get(), reinterpret_cast<uintptr_t>(output_device), io_side::OUTPUT);
    if (r != CUBEB_OK) {
      LOG("(%p) Fail to set device info for output.", stm.get());
      return r;
    }
  }

  {
    // It's not critical to lock here, because no other thread has been started
    // yet, but it allows to assert that the lock has been taken in
    // `audiounit_setup_stream`.
    auto_lock lock(stm->mutex);
    r = audiounit_setup_stream(stm.get());
  }

  if (r != CUBEB_OK) {
    LOG("(%p) Could not setup the audiounit stream.", stm.get());
    return r;
  }

  r = audiounit_install_system_changed_callback(stm.get());
  if (r != CUBEB_OK) {
    LOG("(%p) Could not install the device change callback.", stm.get());
    return r;
  }

  *stream = stm.release();
  LOG("(%p) Cubeb stream init successful.", *stream);
  return CUBEB_OK;
}

static void
audiounit_close_stream(cubeb_stream *stm)
{
  stm->mutex.assert_current_thread_owns();

  if (stm->input_unit) {
    AudioUnitUninitialize(stm->input_unit);
    AudioComponentInstanceDispose(stm->input_unit);
    stm->input_unit = nullptr;
  }

  stm->input_linear_buffer.reset();

  if (stm->output_unit) {
    AudioUnitUninitialize(stm->output_unit);
    AudioComponentInstanceDispose(stm->output_unit);
    stm->output_unit = nullptr;
  }

  stm->resampler.reset();
  stm->mixer.reset();

  if (stm->aggregate_device_id) {
    audiounit_destroy_aggregate_device(stm->plugin_id, &stm->aggregate_device_id);
    stm->aggregate_device_id = 0;
  }
}

static void
audiounit_stream_destroy_internal(cubeb_stream *stm)
{
  stm->context->mutex.assert_current_thread_owns();

  int r = audiounit_uninstall_system_changed_callback(stm);
  if (r != CUBEB_OK) {
    LOG("(%p) Could not uninstall the device changed callback", stm);
  }
  r = audiounit_uninstall_device_changed_callback(stm);
  if (r != CUBEB_OK) {
    LOG("(%p) Could not uninstall all device change listeners", stm);
  }

  auto_lock lock(stm->mutex);
  audiounit_close_stream(stm);
  assert(audiounit_active_streams(stm->context) >= 1);
  audiounit_decrement_active_streams(stm->context);
}

static void
audiounit_stream_destroy(cubeb_stream * stm)
{
  if (!stm->shutdown.load()){
    auto_lock context_lock(stm->context->mutex);
    audiounit_stream_stop_internal(stm);
    stm->shutdown = true;
  }

  stm->destroy_pending = true;
  // Execute close in serial queue to avoid collision
  // with reinit when un/plug devices
  dispatch_sync(stm->context->serial_queue, ^() {
    auto_lock context_lock(stm->context->mutex);
    audiounit_stream_destroy_internal(stm);
  });

  LOG("Cubeb stream (%p) destroyed successful.", stm);
  delete stm;
}

void
audiounit_stream_start_internal(cubeb_stream * stm)
{
  OSStatus r;
  if (stm->input_unit != NULL) {
    r = AudioOutputUnitStart(stm->input_unit);
    assert(r == 0);
  }
  if (stm->output_unit != NULL) {
    r = AudioOutputUnitStart(stm->output_unit);
    assert(r == 0);
  }
}

static int
audiounit_stream_start(cubeb_stream * stm)
{
  auto_lock context_lock(stm->context->mutex);
  stm->shutdown = false;
  stm->draining = false;

  audiounit_stream_start_internal(stm);

  stm->state_callback(stm, stm->user_ptr, CUBEB_STATE_STARTED);

  LOG("Cubeb stream (%p) started successfully.", stm);
  return CUBEB_OK;
}

void
audiounit_stream_stop_internal(cubeb_stream * stm)
{
  OSStatus r;
  if (stm->input_unit != NULL) {
    r = AudioOutputUnitStop(stm->input_unit);
    assert(r == 0);
  }
  if (stm->output_unit != NULL) {
    r = AudioOutputUnitStop(stm->output_unit);
    assert(r == 0);
  }
}

static int
audiounit_stream_stop(cubeb_stream * stm)
{
  auto_lock context_lock(stm->context->mutex);
  stm->shutdown = true;

  audiounit_stream_stop_internal(stm);

  stm->state_callback(stm, stm->user_ptr, CUBEB_STATE_STOPPED);

  LOG("Cubeb stream (%p) stopped successfully.", stm);
  return CUBEB_OK;
}

static int
audiounit_stream_get_position(cubeb_stream * stm, uint64_t * position)
{
  assert(stm);
  if (stm->current_latency_frames > stm->frames_played) {
    *position = 0;
  } else {
    *position = stm->frames_played - stm->current_latency_frames;
  }
  return CUBEB_OK;
}

int
audiounit_stream_get_latency(cubeb_stream * stm, uint32_t * latency)
{
#if TARGET_OS_IPHONE
  //TODO
  return CUBEB_ERROR_NOT_SUPPORTED;
#else
  *latency = stm->current_latency_frames;
  return CUBEB_OK;
#endif
}

static int
audiounit_stream_get_volume(cubeb_stream * stm, float * volume)
{
  assert(stm->output_unit);
  OSStatus r = AudioUnitGetParameter(stm->output_unit,
                                     kHALOutputParam_Volume,
                                     kAudioUnitScope_Global,
                                     0, volume);
  if (r != noErr) {
    LOG("AudioUnitGetParameter/kHALOutputParam_Volume rv=%d", r);
    return CUBEB_ERROR;
  }
  return CUBEB_OK;
}

static int
audiounit_stream_set_volume(cubeb_stream * stm, float volume)
{
  assert(stm->output_unit);
  OSStatus r;
  r = AudioUnitSetParameter(stm->output_unit,
                            kHALOutputParam_Volume,
                            kAudioUnitScope_Global,
                            0, volume, 0);

  if (r != noErr) {
    LOG("AudioUnitSetParameter/kHALOutputParam_Volume rv=%d", r);
    return CUBEB_ERROR;
  }
  return CUBEB_OK;
}

int audiounit_stream_set_panning(cubeb_stream * stm, float panning)
{
  if (stm->output_desc.mChannelsPerFrame > 2) {
    return CUBEB_ERROR_INVALID_PARAMETER;
  }

  stm->panning.store(panning, memory_order_relaxed);
  return CUBEB_OK;
}

unique_ptr<char[]> convert_uint32_into_string(UInt32 data)
{
  // Simply create an empty string if no data.
  size_t size = data == 0 ? 0 : 4; // 4 bytes for uint32.
  auto str = unique_ptr<char[]> { new char[size + 1] }; // + 1 for '\0'.
  str[size] = '\0';
  if (size < 4) {
    return str;
  }

  // Reverse 0xWXYZ into 0xZYXW.
  str[0] = (char)(data >> 24);
  str[1] = (char)(data >> 16);
  str[2] = (char)(data >> 8);
  str[3] = (char)(data);
  return str;
}

int audiounit_get_default_device_datasource(cubeb_device_type type,
                                            UInt32 * data)
{
  AudioDeviceID id = audiounit_get_default_device_id(type);
  if (id == kAudioObjectUnknown) {
    return CUBEB_ERROR;
  }

  UInt32 size = sizeof(*data);
  /* This fails with some USB headsets (e.g., Plantronic .Audio 628). */
  OSStatus r = AudioObjectGetPropertyData(id,
                                          type == CUBEB_DEVICE_TYPE_INPUT ?
                                            &INPUT_DATA_SOURCE_PROPERTY_ADDRESS :
                                            &OUTPUT_DATA_SOURCE_PROPERTY_ADDRESS,
                                          0, NULL, &size, data);
  if (r != noErr) {
    *data = 0;
  }

  return CUBEB_OK;
}

int audiounit_get_default_device_name(cubeb_stream * stm,
                                      cubeb_device * const device,
                                      cubeb_device_type type)
{
  assert(stm);
  assert(device);

  UInt32 data;
  int r = audiounit_get_default_device_datasource(type, &data);
  if (r != CUBEB_OK) {
    return r;
  }
  char ** name = type == CUBEB_DEVICE_TYPE_INPUT ?
    &device->input_name : &device->output_name;
  *name = convert_uint32_into_string(data).release();
  if (!strlen(*name)) { // empty string.
    LOG("(%p) name of %s device is empty!", stm,
        type == CUBEB_DEVICE_TYPE_INPUT ? "input" : "output");
  }
  return CUBEB_OK;
}


int audiounit_stream_get_current_device(cubeb_stream * stm,
                                        cubeb_device ** const device)
{
#if TARGET_OS_IPHONE
  //TODO
  return CUBEB_ERROR_NOT_SUPPORTED;
#else
  *device = new cubeb_device;
  if (!*device) {
    return CUBEB_ERROR;
  }
  PodZero(*device, 1);

  int r = audiounit_get_default_device_name(stm, *device,
                                            CUBEB_DEVICE_TYPE_OUTPUT);
  if (r != CUBEB_OK) {
    return r;
  }

  r = audiounit_get_default_device_name(stm, *device,
                                        CUBEB_DEVICE_TYPE_INPUT);
  if (r != CUBEB_OK) {
    return r;
  }

  return CUBEB_OK;
#endif
}

int audiounit_stream_device_destroy(cubeb_stream * /* stream */,
                                    cubeb_device * device)
{
  delete [] device->output_name;
  delete [] device->input_name;
  delete device;
  return CUBEB_OK;
}

int audiounit_stream_register_device_changed_callback(cubeb_stream * stream,
                                                      cubeb_device_changed_callback device_changed_callback)
{
  auto_lock dev_cb_lock(stream->device_changed_callback_lock);
  /* Note: second register without unregister first causes 'nope' error.
   * Current implementation requires unregister before register a new cb. */
  assert(!stream->device_changed_callback);
  stream->device_changed_callback = device_changed_callback;
  return CUBEB_OK;
}

static char *
audiounit_strref_to_cstr_utf8(CFStringRef strref)
{
  CFIndex len, size;
  char * ret;
  if (strref == NULL) {
    return NULL;
  }

  len = CFStringGetLength(strref);
  // Add 1 to size to allow for '\0' termination character.
  size = CFStringGetMaximumSizeForEncoding(len, kCFStringEncodingUTF8) + 1;
  ret = new char[size];

  if (!CFStringGetCString(strref, ret, size, kCFStringEncodingUTF8)) {
    delete [] ret;
    ret = NULL;
  }

  return ret;
}

static uint32_t
audiounit_get_channel_count(AudioObjectID devid, AudioObjectPropertyScope scope)
{
  AudioObjectPropertyAddress adr = { 0, scope, kAudioObjectPropertyElementMaster };
  UInt32 size = 0;
  uint32_t i, ret = 0;

  adr.mSelector = kAudioDevicePropertyStreamConfiguration;

  if (AudioObjectGetPropertyDataSize(devid, &adr, 0, NULL, &size) == noErr && size > 0) {
    AudioBufferList * list = static_cast<AudioBufferList *>(alloca(size));
    if (AudioObjectGetPropertyData(devid, &adr, 0, NULL, &size, list) == noErr) {
      for (i = 0; i < list->mNumberBuffers; i++)
        ret += list->mBuffers[i].mNumberChannels;
    }
  }

  return ret;
}

static void
audiounit_get_available_samplerate(AudioObjectID devid, AudioObjectPropertyScope scope,
                                   uint32_t * min, uint32_t * max, uint32_t * def)
{
  AudioObjectPropertyAddress adr = { 0, scope, kAudioObjectPropertyElementMaster };

  adr.mSelector = kAudioDevicePropertyNominalSampleRate;
  if (AudioObjectHasProperty(devid, &adr)) {
    UInt32 size = sizeof(Float64);
    Float64 fvalue = 0.0;
    if (AudioObjectGetPropertyData(devid, &adr, 0, NULL, &size, &fvalue) == noErr) {
      *def = fvalue;
    }
  }

  adr.mSelector = kAudioDevicePropertyAvailableNominalSampleRates;
  UInt32 size = 0;
  AudioValueRange range;
  if (AudioObjectHasProperty(devid, &adr) &&
      AudioObjectGetPropertyDataSize(devid, &adr, 0, NULL, &size) == noErr) {
    uint32_t count = size / sizeof(AudioValueRange);
    vector<AudioValueRange> ranges(count);
    range.mMinimum = 9999999999.0;
    range.mMaximum = 0.0;
    if (AudioObjectGetPropertyData(devid, &adr, 0, NULL, &size, ranges.data()) == noErr) {
      for (uint32_t i = 0; i < count; i++) {
        if (ranges[i].mMaximum > range.mMaximum)
          range.mMaximum = ranges[i].mMaximum;
        if (ranges[i].mMinimum < range.mMinimum)
          range.mMinimum = ranges[i].mMinimum;
      }
    }
    *max = static_cast<uint32_t>(range.mMaximum);
    *min = static_cast<uint32_t>(range.mMinimum);
  } else {
    *min = *max = 0;
  }

}

static UInt32
audiounit_get_device_presentation_latency(AudioObjectID devid, AudioObjectPropertyScope scope)
{
  AudioObjectPropertyAddress adr = { 0, scope, kAudioObjectPropertyElementMaster };
  UInt32 size, dev, stream = 0;
  AudioStreamID sid[1];

  adr.mSelector = kAudioDevicePropertyLatency;
  size = sizeof(UInt32);
  if (AudioObjectGetPropertyData(devid, &adr, 0, NULL, &size, &dev) != noErr) {
    dev = 0;
  }

  adr.mSelector = kAudioDevicePropertyStreams;
  size = sizeof(sid);
  if (AudioObjectGetPropertyData(devid, &adr, 0, NULL, &size, sid) == noErr) {
    adr.mSelector = kAudioStreamPropertyLatency;
    size = sizeof(UInt32);
    AudioObjectGetPropertyData(sid[0], &adr, 0, NULL, &size, &stream);
  }

  return dev + stream;
}

static int
audiounit_create_device_from_hwdev(cubeb_device_info * dev_info, AudioObjectID devid, cubeb_device_type type)
{
  AudioObjectPropertyAddress adr = { 0, 0, kAudioObjectPropertyElementMaster };
  UInt32 size;

  if (type == CUBEB_DEVICE_TYPE_OUTPUT) {
    adr.mScope = kAudioDevicePropertyScopeOutput;
  } else if (type == CUBEB_DEVICE_TYPE_INPUT) {
    adr.mScope = kAudioDevicePropertyScopeInput;
  } else {
    return CUBEB_ERROR;
  }

  UInt32 ch = audiounit_get_channel_count(devid, adr.mScope);
  if (ch == 0) {
    return CUBEB_ERROR;
  }

  PodZero(dev_info, 1);

  CFStringRef device_id_str = nullptr;
  size = sizeof(CFStringRef);
  adr.mSelector = kAudioDevicePropertyDeviceUID;
  OSStatus ret = AudioObjectGetPropertyData(devid, &adr, 0, NULL, &size, &device_id_str);
  if ( ret == noErr && device_id_str != NULL) {
    dev_info->device_id = audiounit_strref_to_cstr_utf8(device_id_str);
    static_assert(sizeof(cubeb_devid) >= sizeof(decltype(devid)), "cubeb_devid can't represent devid");
    dev_info->devid = reinterpret_cast<cubeb_devid>(devid);
    dev_info->group_id = dev_info->device_id;
    CFRelease(device_id_str);
  }

  CFStringRef friendly_name_str = nullptr;
  UInt32 ds;
  size = sizeof(UInt32);
  adr.mSelector = kAudioDevicePropertyDataSource;
  ret = AudioObjectGetPropertyData(devid, &adr, 0, NULL, &size, &ds);
  if (ret == noErr) {
    AudioValueTranslation trl = { &ds, sizeof(ds), &friendly_name_str, sizeof(CFStringRef) };
    adr.mSelector = kAudioDevicePropertyDataSourceNameForIDCFString;
    size = sizeof(AudioValueTranslation);
    AudioObjectGetPropertyData(devid, &adr, 0, NULL, &size, &trl);
  }

  // If there is no datasource for this device, fall back to the
  // device name.
  if (!friendly_name_str) {
    size = sizeof(CFStringRef);
    adr.mSelector = kAudioObjectPropertyName;
    AudioObjectGetPropertyData(devid, &adr, 0, NULL, &size, &friendly_name_str);
  }

  if (friendly_name_str) {
    dev_info->friendly_name = audiounit_strref_to_cstr_utf8(friendly_name_str);
    CFRelease(friendly_name_str);
  } else {
    // Couldn't get a datasource name nor a device name, return a
    // valid string of length 0.
    char * fallback_name = new char[1];
    fallback_name[0] = '\0';
    dev_info->friendly_name = fallback_name;
  }

  CFStringRef vendor_name_str = nullptr;
  size = sizeof(CFStringRef);
  adr.mSelector = kAudioObjectPropertyManufacturer;
  ret = AudioObjectGetPropertyData(devid, &adr, 0, NULL, &size, &vendor_name_str);
  if (ret == noErr && vendor_name_str != NULL) {
    dev_info->vendor_name = audiounit_strref_to_cstr_utf8(vendor_name_str);
    CFRelease(vendor_name_str);
  }

  dev_info->type = type;
  dev_info->state = CUBEB_DEVICE_STATE_ENABLED;
  dev_info->preferred = (devid == audiounit_get_default_device_id(type)) ?
    CUBEB_DEVICE_PREF_ALL : CUBEB_DEVICE_PREF_NONE;

  dev_info->max_channels = ch;
  dev_info->format = (cubeb_device_fmt)CUBEB_DEVICE_FMT_ALL; /* CoreAudio supports All! */
  /* kAudioFormatFlagsAudioUnitCanonical is deprecated, prefer floating point */
  dev_info->default_format = CUBEB_DEVICE_FMT_F32NE;
  audiounit_get_available_samplerate(devid, adr.mScope,
                                     &dev_info->min_rate, &dev_info->max_rate, &dev_info->default_rate);

  UInt32 latency = audiounit_get_device_presentation_latency(devid, adr.mScope);

  AudioValueRange range;
  adr.mSelector = kAudioDevicePropertyBufferFrameSizeRange;
  size = sizeof(AudioValueRange);
  ret = AudioObjectGetPropertyData(devid, &adr, 0, NULL, &size, &range);
  if (ret == noErr) {
    dev_info->latency_lo = latency + range.mMinimum;
    dev_info->latency_hi = latency + range.mMaximum;
  } else {
    dev_info->latency_lo = 10 * dev_info->default_rate / 1000;  /* Default to 10ms */
    dev_info->latency_hi = 100 * dev_info->default_rate / 1000; /* Default to 100ms */
  }

  return CUBEB_OK;
}

bool
is_aggregate_device(cubeb_device_info * device_info)
{
  assert(device_info->friendly_name);
  return !strncmp(device_info->friendly_name, PRIVATE_AGGREGATE_DEVICE_NAME,
                  strlen(PRIVATE_AGGREGATE_DEVICE_NAME));
}

static int
audiounit_enumerate_devices(cubeb * /* context */, cubeb_device_type type,
                            cubeb_device_collection * collection)
{
  vector<AudioObjectID> input_devs;
  vector<AudioObjectID> output_devs;

  // Count number of input and output devices.  This is not
  // necessarily the same as the count of raw devices supported by the
  // system since, for example, with Soundflower installed, some
  // devices may report as being both input *and* output and cubeb
  // separates those into two different devices.

  if (type & CUBEB_DEVICE_TYPE_OUTPUT) {
    output_devs = audiounit_get_devices_of_type(CUBEB_DEVICE_TYPE_OUTPUT);
  }

  if (type & CUBEB_DEVICE_TYPE_INPUT) {
    input_devs = audiounit_get_devices_of_type(CUBEB_DEVICE_TYPE_INPUT);
  }

  auto devices = new cubeb_device_info[output_devs.size() + input_devs.size()];
  collection->count = 0;

  if (type & CUBEB_DEVICE_TYPE_OUTPUT) {
    for (auto dev: output_devs) {
      auto device = &devices[collection->count];
      auto err = audiounit_create_device_from_hwdev(device, dev, CUBEB_DEVICE_TYPE_OUTPUT);
      if (err != CUBEB_OK || is_aggregate_device(device)) {
        continue;
      }
      collection->count += 1;
    }
  }

  if (type & CUBEB_DEVICE_TYPE_INPUT) {
    for (auto dev: input_devs) {
      auto device = &devices[collection->count];
      auto err = audiounit_create_device_from_hwdev(device, dev, CUBEB_DEVICE_TYPE_INPUT);
      if (err != CUBEB_OK || is_aggregate_device(device)) {
        continue;
      }
      collection->count += 1;
    }
  }

  if (collection->count > 0) {
    collection->device = devices;
  } else {
    delete [] devices;
    collection->device = NULL;
  }

  return CUBEB_OK;
}

static int
audiounit_device_collection_destroy(cubeb * /* context */,
                                    cubeb_device_collection * collection)
{
  for (size_t i = 0; i < collection->count; i++) {
    delete [] collection->device[i].device_id;
    delete [] collection->device[i].friendly_name;
    delete [] collection->device[i].vendor_name;
  }
  delete [] collection->device;

  return CUBEB_OK;
}

static vector<AudioObjectID>
audiounit_get_devices_of_type(cubeb_device_type devtype)
{
  UInt32 size = 0;
  OSStatus ret = AudioObjectGetPropertyDataSize(kAudioObjectSystemObject,
                                                &DEVICES_PROPERTY_ADDRESS, 0,
                                                NULL, &size);
  if (ret != noErr) {
    return vector<AudioObjectID>();
  }
  vector<AudioObjectID> devices(size / sizeof(AudioObjectID));
  ret = AudioObjectGetPropertyData(kAudioObjectSystemObject,
                                   &DEVICES_PROPERTY_ADDRESS, 0, NULL, &size,
                                   devices.data());
  if (ret != noErr) {
    return vector<AudioObjectID>();
  }

  // Remove the aggregate device from the list of devices (if any).
  for (auto it = devices.begin(); it != devices.end();) {
    CFStringRef name = get_device_name(*it);
    if (CFStringFind(name, CFSTR("CubebAggregateDevice"), 0).location !=
        kCFNotFound) {
      it = devices.erase(it);
    } else {
      it++;
    }
  }

  /* Expected sorted but did not find anything in the docs. */
  sort(devices.begin(), devices.end(), [](AudioObjectID a, AudioObjectID b) {
      return a < b;
    });

  if (devtype == (CUBEB_DEVICE_TYPE_INPUT | CUBEB_DEVICE_TYPE_OUTPUT)) {
    return devices;
  }

  AudioObjectPropertyScope scope = (devtype == CUBEB_DEVICE_TYPE_INPUT) ?
                                         kAudioDevicePropertyScopeInput :
                                         kAudioDevicePropertyScopeOutput;

  vector<AudioObjectID> devices_in_scope;
  for (uint32_t i = 0; i < devices.size(); ++i) {
    /* For device in the given scope channel must be > 0. */
    if (audiounit_get_channel_count(devices[i], scope) > 0) {
      devices_in_scope.push_back(devices[i]);
    }
  }

  return devices_in_scope;
}

static OSStatus
audiounit_collection_changed_callback(AudioObjectID /* inObjectID */,
                                      UInt32 /* inNumberAddresses */,
                                      const AudioObjectPropertyAddress * /* inAddresses */,
                                      void * inClientData)
{
  cubeb * context = static_cast<cubeb *>(inClientData);

  // This can be called from inside an AudioUnit function, dispatch to another queue.
  dispatch_async(context->serial_queue, ^() {
    auto_lock lock(context->mutex);
    if (context->collection_changed_callback == NULL) {
      /* Listener removed while waiting in mutex, abort. */
      return;
    }

    assert(context->collection_changed_devtype &
           (CUBEB_DEVICE_TYPE_INPUT | CUBEB_DEVICE_TYPE_OUTPUT));

    vector<AudioObjectID> devices = audiounit_get_devices_of_type(context->collection_changed_devtype);
    /* The elements in the vector are sorted. */
    if (context->devtype_device_array == devices) {
      /* Device changed for the other scope, ignore. */
      return;
    }
    /* Device on desired scope has changed. */
    context->devtype_device_array = devices;
    context->collection_changed_callback(context, context->collection_changed_user_ptr);
  });
  return noErr;
}

static OSStatus
audiounit_add_device_listener(cubeb * context,
                              cubeb_device_type devtype,
                              cubeb_device_collection_changed_callback collection_changed_callback,
                              void * user_ptr)
{
  /* Note: second register without unregister first causes 'nope' error.
   * Current implementation requires unregister before register a new cb. */
  assert(context->collection_changed_callback == NULL);

  OSStatus ret = AudioObjectAddPropertyListener(kAudioObjectSystemObject,
                                                &DEVICES_PROPERTY_ADDRESS,
                                                audiounit_collection_changed_callback,
                                                context);
  if (ret == noErr) {
    /* Expected empty after unregister. */
    assert(context->devtype_device_array.empty());
    /* Listener works for input and output.
     * When requested one of them we need to differentiate. */
    assert(devtype &
           (CUBEB_DEVICE_TYPE_INPUT | CUBEB_DEVICE_TYPE_OUTPUT));
    context->devtype_device_array = audiounit_get_devices_of_type(devtype);
    context->collection_changed_devtype = devtype;
    context->collection_changed_callback = collection_changed_callback;
    context->collection_changed_user_ptr = user_ptr;
  }
  return ret;
}

static OSStatus
audiounit_remove_device_listener(cubeb * context)
{
  /* Note: unregister a non registered cb is not a problem, not checking. */
  OSStatus ret = AudioObjectRemovePropertyListener(kAudioObjectSystemObject,
                                                   &DEVICES_PROPERTY_ADDRESS,
                                                   audiounit_collection_changed_callback,
                                                   context);
  if (ret == noErr) {
    /* Reset all values. */
    context->collection_changed_devtype = CUBEB_DEVICE_TYPE_UNKNOWN;
    context->collection_changed_callback = NULL;
    context->collection_changed_user_ptr = NULL;
    context->devtype_device_array.clear();
  }
  return ret;
}

int audiounit_register_device_collection_changed(cubeb * context,
                                                 cubeb_device_type devtype,
                                                 cubeb_device_collection_changed_callback collection_changed_callback,
                                                 void * user_ptr)
{
  OSStatus ret;
  auto_lock lock(context->mutex);
  if (collection_changed_callback) {
    ret = audiounit_add_device_listener(context, devtype,
                                        collection_changed_callback,
                                        user_ptr);
  } else {
    ret = audiounit_remove_device_listener(context);
  }
  return (ret == noErr) ? CUBEB_OK : CUBEB_ERROR;
}

cubeb_ops const audiounit_ops = {
  /*.init =*/ audiounit_init,
  /*.get_backend_id =*/ audiounit_get_backend_id,
  /*.get_max_channel_count =*/ audiounit_get_max_channel_count,
  /*.get_min_latency =*/ audiounit_get_min_latency,
  /*.get_preferred_sample_rate =*/ audiounit_get_preferred_sample_rate,
  /*.enumerate_devices =*/ audiounit_enumerate_devices,
  /*.device_collection_destroy =*/ audiounit_device_collection_destroy,
  /*.destroy =*/ audiounit_destroy,
  /*.stream_init =*/ audiounit_stream_init,
  /*.stream_destroy =*/ audiounit_stream_destroy,
  /*.stream_start =*/ audiounit_stream_start,
  /*.stream_stop =*/ audiounit_stream_stop,
  /*.stream_reset_default_device =*/ nullptr,
  /*.stream_get_position =*/ audiounit_stream_get_position,
  /*.stream_get_latency =*/ audiounit_stream_get_latency,
  /*.stream_set_volume =*/ audiounit_stream_set_volume,
  /*.stream_set_panning =*/ audiounit_stream_set_panning,
  /*.stream_get_current_device =*/ audiounit_stream_get_current_device,
  /*.stream_device_destroy =*/ audiounit_stream_device_destroy,
  /*.stream_register_device_changed_callback =*/ audiounit_stream_register_device_changed_callback,
  /*.register_device_collection_changed =*/ audiounit_register_device_collection_changed
};