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;
  }
}

bool
is_common_sample_rate(Float64 sample_rate)
{
  /* Some commonly used sample rates and their multiples and divisors. */
  return sample_rate == 8000 || sample_rate == 16000 || sample_rate == 22050 ||
         sample_rate == 32000 || sample_rate == 44100 || sample_rate == 48000 ||
         sample_rate == 88200 || sample_rate == 96000;
}

#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);
  if (outframes < 0) {
    stm->shutdown = true;
    OSStatus r = AudioOutputUnitStop(stm->input_unit);
    assert(r == 0);
    stm->state_callback(stm, stm->user_ptr, CUBEB_STATE_ERROR);
    return noErr;
  }
  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));
    }

    // Destroying a cubeb context with device collection callbacks registered
    // is misuse of the API, assert then attempt to clean up.
    assert(!ctx->input_collection_changed_callback &&
           !ctx->input_collection_changed_user_ptr &&
           !ctx->output_collection_changed_callback &&
           !ctx->output_collection_changed_user_ptr);

    /* 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;
  if (!is_common_sample_rate(stm->output_desc.mSampleRate)) {
    /* For uncommon sample rates, we may run into issues with the OS
       resampler if we don't do the resampling ourselves, so set the
       AudioUnit sample rate to the hardware rate and resample. */
    stm->output_desc.mSampleRate = stm->output_hw_rate;
  }
  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;
  }

  cubeb_stream_params output_unconverted_params;
  if (has_output(stm)) {
    output_unconverted_params = stm->output_stream_params;
    output_unconverted_params.rate = stm->output_desc.mSampleRate;
  }

  /* Create resampler. */
  stm->resampler.reset(cubeb_resampler_create(
      stm, has_input(stm) ? &input_unconverted_params : NULL,
      has_output(stm) ? &output_unconverted_params : NULL, target_sample_rate,
      stm->data_callback, stm->user_ptr, CUBEB_RESAMPLER_QUALITY_DESKTOP,
      CUBEB_RESAMPLER_RECLOCK_NONE));
  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,
    /*.get_supported_input_processing_params =*/NULL,
    /*.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_set_input_mute =*/NULL,
    /*.stream_set_input_processing_params =*/NULL,
    /*.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};