cubeb/src/cubeb_audiounit.cpp

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

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

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 = 128;
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);
static int
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 input_collection_changed_callback =
      nullptr;
  void * input_collection_changed_user_ptr = nullptr;
  cubeb_device_collection_changed_callback output_collection_changed_callback =
      nullptr;
  void * output_collection_changed_user_ptr = nullptr;
  // Store list of devices to detect changes
  vector<AudioObjectID> input_device_array;
  vector<AudioObjectID> output_device_array;
  // The queue should be released when it’s no longer needed.
  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<uint32_t> total_output_latency_frames{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 =
      kAudioObjectUnknown; // the aggregate device id
  AudioObjectID plugin_id =
      kAudioObjectUnknown; // 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

#endif

uint64_t
ConvertHostTimeToNanos(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;
}

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;
  }

  if (stm->draining) {
    OSStatus r = AudioOutputUnitStop(stm->input_unit);
    assert(r == 0);
    // Only fire state callback in input-only stream. For duplex stream,
    // the state callback will be fired in output callback.
    if (stm->output_unit == NULL) {
      stm->state_callback(stm, stm->user_ptr, CUBEB_STATE_DRAINED);
    }
    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);
  stm->draining = outframes < total_input_frames;

  // 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);

  uint64_t now = ConvertHostTimeToNanos(mach_absolute_time());
  uint64_t audio_output_time = ConvertHostTimeToNanos(tstamp->mHostTime);
  uint64_t output_latency_ns = audio_output_time - now;

  const int ns2s = 1e9;
  // The total output latency is the timestamp difference + the stream latency +
  // the hardware latency.
  stm->total_output_latency_frames =
      output_latency_ns * stm->output_hw_rate / ns2s +
      stm->current_latency_frames;

  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);
    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;

  /* Post process output samples. */
  if (stm->draining) {
    /* Clear missing frames (silence) */
    size_t channels = stm->output_stream_params.channels;
    size_t missing_samples = (output_frames - outframes) * channels;
    size_t size_sample = cubeb_sample_size(stm->output_stream_params.format);
    /* number of bytes that have been filled with valid audio by the callback.
     */
    size_t audio_byte_count = outframes * channels * size_sample;
    PodZero((uint8_t *)output_buffer + audio_byte_count,
            missing_samples * size_sample);
  }

  /* 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);
  }

  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 : kAudioObjectUnknown;
    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, kAudioObjectUnknown, 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 != kAudioObjectUnknown) {
        // Attempt to re-use the same device-id failed, so attempt again with
        // default input device.
        audiounit_close_stream(stm);
        if (audiounit_set_device_info(stm, kAudioObjectUnknown,
                                      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) {
      r = audiounit_stream_start_internal(stm);
      if (r != CUBEB_OK) {
        return CUBEB_ERROR;
      }
    }
  }
  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 == kAudioDevicePropertyDataSource 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 one 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, cubeb_device_type devtype);

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->input_collection_changed_callback) {
      audiounit_remove_device_listener(ctx, CUBEB_DEVICE_TYPE_INPUT);
    }
    if (ctx->output_collection_changed_callback) {
      audiounit_remove_device_listener(ctx, CUBEB_DEVICE_TYPE_OUTPUT);
    }
  }

  dispatch_release(ctx->serial_queue);

  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("AudioObjectGetPropertyDataSize/"
        "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("AudioObjectGetPropertyData/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;
}

// The returned CFStringRef object needs to be released (via CFRelease)
// if it's not NULL, since the reference count of the returned CFStringRef
// object is increased.
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);
    CFRelease(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);
    CFRelease(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 != kAudioObjectUnknown);
  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 (master_sub_device) {
    CFRelease(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 != kAudioObjectUnknown);
  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_device_destroy(cubeb_device_info * device);

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);
    }
  }
  audiounit_device_destroy(&input_device_info);
  audiounit_device_destroy(&output_device_info);
}

/*
 * 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 = kAudioObjectUnknown;
  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 = kAudioObjectUnknown;
      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 latency 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); // Ugly 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 != kAudioObjectUnknown) {
    audiounit_destroy_aggregate_device(stm->plugin_id,
                                       &stm->aggregate_device_id);
    stm->aggregate_device_id = kAudioObjectUnknown;
  }
}

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)
{
  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);
  }

  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;
}

static int
audiounit_stream_start_internal(cubeb_stream * stm)
{
  OSStatus r;
  if (stm->input_unit != NULL) {
    r = AudioOutputUnitStart(stm->input_unit);
    if (r != noErr) {
      LOG("AudioOutputUnitStart (input) rv=%d", r);
      return CUBEB_ERROR;
    }
  }
  if (stm->output_unit != NULL) {
    r = AudioOutputUnitStart(stm->output_unit);
    if (r != noErr) {
      LOG("AudioOutputUnitStart (output) rv=%d", r);
      return CUBEB_ERROR;
    }
  }
  return CUBEB_OK;
}

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

  int r = audiounit_stream_start_internal(stm);
  if (r != CUBEB_OK) {
    return r;
  }

  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->total_output_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;
}

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(!device_changed_callback || !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 void
audiounit_device_destroy(cubeb_device_info * device)
{
  delete[] device->device_id;
  delete[] device->friendly_name;
  delete[] device->vendor_name;
}

static int
audiounit_device_collection_destroy(cubeb * /* context */,
                                    cubeb_device_collection * collection)
{
  for (size_t i = 0; i < collection->count; i++) {
    audiounit_device_destroy(&collection->device[i]);
  }
  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 (name && CFStringFind(name, CFSTR("CubebAggregateDevice"), 0).location !=
                    kCFNotFound) {
      it = devices.erase(it);
    } else {
      it++;
    }
    if (name) {
      CFRelease(name);
    }
  }

  /* 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->input_collection_changed_callback &&
        !context->output_collection_changed_callback) {
      /* Listener removed while waiting in mutex, abort. */
      return;
    }
    if (context->input_collection_changed_callback) {
      vector<AudioObjectID> devices =
          audiounit_get_devices_of_type(CUBEB_DEVICE_TYPE_INPUT);
      /* Elements in the vector expected sorted. */
      if (context->input_device_array != devices) {
        context->input_device_array = devices;
        context->input_collection_changed_callback(
            context, context->input_collection_changed_user_ptr);
      }
    }
    if (context->output_collection_changed_callback) {
      vector<AudioObjectID> devices =
          audiounit_get_devices_of_type(CUBEB_DEVICE_TYPE_OUTPUT);
      /* Elements in the vector expected sorted. */
      if (context->output_device_array != devices) {
        context->output_device_array = devices;
        context->output_collection_changed_callback(
            context, context->output_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)
{
  context->mutex.assert_current_thread_owns();
  assert(devtype & (CUBEB_DEVICE_TYPE_INPUT | CUBEB_DEVICE_TYPE_OUTPUT));
  /* Note: second register without unregister first causes 'nope' error.
   * Current implementation requires unregister before register a new cb. */
  assert((devtype & CUBEB_DEVICE_TYPE_INPUT) &&
             !context->input_collection_changed_callback ||
         (devtype & CUBEB_DEVICE_TYPE_OUTPUT) &&
             !context->output_collection_changed_callback);

  if (!context->input_collection_changed_callback &&
      !context->output_collection_changed_callback) {
    OSStatus ret = AudioObjectAddPropertyListener(
        kAudioObjectSystemObject, &DEVICES_PROPERTY_ADDRESS,
        audiounit_collection_changed_callback, context);
    if (ret != noErr) {
      return ret;
    }
  }
  if (devtype & CUBEB_DEVICE_TYPE_INPUT) {
    /* Expected empty after unregister. */
    assert(context->input_device_array.empty());
    context->input_device_array =
        audiounit_get_devices_of_type(CUBEB_DEVICE_TYPE_INPUT);
    context->input_collection_changed_callback = collection_changed_callback;
    context->input_collection_changed_user_ptr = user_ptr;
  }
  if (devtype & CUBEB_DEVICE_TYPE_OUTPUT) {
    /* Expected empty after unregister. */
    assert(context->output_device_array.empty());
    context->output_device_array =
        audiounit_get_devices_of_type(CUBEB_DEVICE_TYPE_OUTPUT);
    context->output_collection_changed_callback = collection_changed_callback;
    context->output_collection_changed_user_ptr = user_ptr;
  }
  return noErr;
}

static OSStatus
audiounit_remove_device_listener(cubeb * context, cubeb_device_type devtype)
{
  context->mutex.assert_current_thread_owns();

  if (devtype & CUBEB_DEVICE_TYPE_INPUT) {
    context->input_collection_changed_callback = nullptr;
    context->input_collection_changed_user_ptr = nullptr;
    context->input_device_array.clear();
  }
  if (devtype & CUBEB_DEVICE_TYPE_OUTPUT) {
    context->output_collection_changed_callback = nullptr;
    context->output_collection_changed_user_ptr = nullptr;
    context->output_device_array.clear();
  }

  if (context->input_collection_changed_callback ||
      context->output_collection_changed_callback) {
    return noErr;
  }
  /* Note: unregister a non registered cb is not a problem, not checking. */
  return AudioObjectRemovePropertyListener(
      kAudioObjectSystemObject, &DEVICES_PROPERTY_ADDRESS,
      audiounit_collection_changed_callback, context);
}

int
audiounit_register_device_collection_changed(
    cubeb * context, cubeb_device_type devtype,
    cubeb_device_collection_changed_callback collection_changed_callback,
    void * user_ptr)
{
  if (devtype == CUBEB_DEVICE_TYPE_UNKNOWN) {
    return CUBEB_ERROR_INVALID_PARAMETER;
  }
  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, devtype);
  }
  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_get_position =*/audiounit_stream_get_position,
    /*.stream_get_latency =*/audiounit_stream_get_latency,
    /*.stream_get_input_latency =*/NULL,
    /*.stream_set_volume =*/audiounit_stream_set_volume,
    /*.stream_set_name =*/NULL,
    /*.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};