Merge branch 'master' into mailnews-work

1 files changed, 1937 insertions, 1053 deletions

diff --git a/media/libcubeb/src/cubeb_audiounit.cpp b/media/libcubeb/src/cubeb_audiounit.cpp
index 9483c2795..e0c8fc696 100644
--- a/media/libcubeb/src/cubeb_audiounit.cpp
+++ b/media/libcubeb/src/cubeb_audiounit.cpp
@@ -22,200 +22,243 @@
 #include <AudioToolbox/AudioToolbox.h>
 #include "cubeb/cubeb.h"
 #include "cubeb-internal.h"
-#include "cubeb_panner.h"
+#include "cubeb_mixer.h"
 #if !TARGET_OS_IPHONE
 #include "cubeb_osx_run_loop.h"
 #endif
 #include "cubeb_resampler.h"
 #include "cubeb_ring_array.h"
-#include "cubeb_utils.h"
 #include <algorithm>
 #include <atomic>
+#include <vector>
+#include <set>
+#include <sys/time.h>
+#include <string>
 
-#if !defined(kCFCoreFoundationVersionNumber10_7)
-/* From CoreFoundation CFBase.h */
-#define kCFCoreFoundationVersionNumber10_7 635.00
-#endif
-
-#if !TARGET_OS_IPHONE && MAC_OS_X_VERSION_MIN_REQUIRED < 1060
-#define AudioComponent Component
-#define AudioComponentDescription ComponentDescription
-#define AudioComponentFindNext FindNextComponent
-#define AudioComponentInstanceNew OpenAComponent
-#define AudioComponentInstanceDispose CloseComponent
-#endif
+using namespace std;
 
 #if MAC_OS_X_VERSION_MIN_REQUIRED < 101000
-typedef UInt32  AudioFormatFlags;
+typedef UInt32 AudioFormatFlags;
 #endif
 
-#define CUBEB_STREAM_MAX 8
-
 #define AU_OUT_BUS    0
 #define AU_IN_BUS     1
 
-#define PRINT_ERROR_CODE(str, r) do {                                \
-  LOG("System call failed: %s (rv: %d)", str, r);                    \
-} while(0)
-
 const char * DISPATCH_QUEUE_LABEL = "org.mozilla.cubeb";
+const char * PRIVATE_AGGREGATE_DEVICE_NAME = "CubebAggregateDevice";
+
+#ifdef ALOGV
+#undef ALOGV
+#endif
+#define ALOGV(msg, ...) dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{LOGV(msg, ##__VA_ARGS__);})
+
+#ifdef ALOG
+#undef ALOG
+#endif
+#define ALOG(msg, ...) dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{LOG(msg, ##__VA_ARGS__);})
 
 /* Testing empirically, some headsets report a minimal latency that is very
  * low, but this does not work in practice. Lie and say the minimum is 256
  * frames. */
-const uint32_t SAFE_MIN_LATENCY_FRAMES = 256;
+const uint32_t SAFE_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);
-void audiounit_stream_start_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;
+  cubeb_ops const * ops = &audiounit_ops;
   owned_critical_section mutex;
-  std::atomic<int> active_streams;
+  int active_streams = 0;
   uint32_t global_latency_frames = 0;
-  int limit_streams;
-  cubeb_device_collection_changed_callback collection_changed_callback;
-  void * collection_changed_user_ptr;
-  /* Differentiate input from output devices. */
-  cubeb_device_type collection_changed_devtype;
-  uint32_t devtype_device_count;
-  AudioObjectID * devtype_device_array;
-  // The queue is asynchronously deallocated once all references to it are released
+  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;
 };
 
-class auto_array_wrapper
+static unique_ptr<AudioChannelLayout, decltype(&free)>
+make_sized_audio_channel_layout(size_t sz)
 {
-public:
-  explicit auto_array_wrapper(auto_array<float> * ar)
-  : float_ar(ar)
-  , short_ar(nullptr)
-  {assert((float_ar && !short_ar) || (!float_ar && short_ar));}
-
-  explicit auto_array_wrapper(auto_array<short> * ar)
-  : float_ar(nullptr)
-  , short_ar(ar)
-  {assert((float_ar && !short_ar) || (!float_ar && short_ar));}
-
-  ~auto_array_wrapper() {
-    auto_lock l(lock);
-    assert((float_ar && !short_ar) || (!float_ar && short_ar));
-    delete float_ar;
-    delete short_ar;
-  }
-
-  void push(void * elements, size_t length){
-    assert((float_ar && !short_ar) || (!float_ar && short_ar));
-    auto_lock l(lock);
-    if (float_ar)
-      return float_ar->push(static_cast<float*>(elements), length);
-    return short_ar->push(static_cast<short*>(elements), length);
-  }
-
-  size_t length() {
-    assert((float_ar && !short_ar) || (!float_ar && short_ar));
-    auto_lock l(lock);
-    if (float_ar)
-      return float_ar->length();
-    return short_ar->length();
-  }
-
-  void push_silence(size_t length) {
-    assert((float_ar && !short_ar) || (!float_ar && short_ar));
-    auto_lock l(lock);
-    if (float_ar)
-      return float_ar->push_silence(length);
-    return short_ar->push_silence(length);
-  }
+    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);
+}
 
-  bool pop(void * elements, size_t length) {
-    assert((float_ar && !short_ar) || (!float_ar && short_ar));
-    auto_lock l(lock);
-    if (float_ar)
-      return float_ar->pop(static_cast<float*>(elements), length);
-    return short_ar->pop(static_cast<short*>(elements), length);
-  }
+enum class io_side {
+  INPUT,
+  OUTPUT,
+};
 
-  void * data() {
-    assert((float_ar && !short_ar) || (!float_ar && short_ar));
-    auto_lock l(lock);
-    if (float_ar)
-      return float_ar->data();
-    return short_ar->data();
+static char const *
+to_string(io_side side)
+{
+  switch (side) {
+  case io_side::INPUT:
+    return "input";
+  case io_side::OUTPUT:
+    return "output";
   }
+}
 
-  void clear() {
-    assert((float_ar && !short_ar) || (!float_ar && short_ar));
-    auto_lock l(lock);
-    if (float_ar) {
-      float_ar->clear();
-    } else {
-      short_ar->clear();
-    }
-  }
+struct device_info {
+  AudioDeviceID id = kAudioObjectUnknown;
+  device_flags_value flags = DEV_UNKNOWN;
+};
 
-private:
-  auto_array<float> * float_ar;
-  auto_array<short> * short_ar;
-  owned_critical_section lock;
+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;
-  cubeb_data_callback data_callback;
-  cubeb_state_callback state_callback;
-  cubeb_device_changed_callback device_changed_callback;
+  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_stream_params output_stream_params;
-  cubeb_devid input_device;
-  bool is_default_input;
-  cubeb_devid output_device;
-  /* User pointer of data_callback */
-  void * user_ptr;
+  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;
-  AudioUnit output_unit;
+  AudioUnit input_unit = nullptr;
+  AudioUnit output_unit = nullptr;
   /* I/O device sample rate */
-  Float64 input_hw_rate;
-  Float64 output_hw_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;
+  int expected_output_callbacks_in_a_row = 0;
   owned_critical_section mutex;
-  /* Hold the input samples in every
-   * input callback iteration */
-  auto_array_wrapper * input_linear_buffer;
-  /* Frames on input buffer */
-  std::atomic<uint32_t> input_buffer_frames;
+  // 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 */
-  uint64_t frames_played;
-  uint64_t frames_queued;
-  std::atomic<int64_t> frames_read;
-  std::atomic<bool> shutdown;
-  std::atomic<bool> draining;
+  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;
-  std::atomic<uint64_t> current_latency_frames;
-  uint64_t hw_latency_frames;
-  std::atomic<float> panning;
-  cubeb_resampler * resampler;
-  /* This is the number of output callback we got in a row. This is usually one,
-   * but can be two when the input and output rate are different, and more when
-   * a device has been plugged or unplugged, as there can be some time before
-   * the device is ready. */
-  std::atomic<int> output_callback_in_a_row;
+  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.  */
-  std::atomic<bool> switching_device;
-  std::atomic<bool> buffer_size_change_state{ false };
+  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)
@@ -228,14 +271,106 @@ bool has_output(cubeb_stream * stm)
   return stm->output_stream_params.rate != 0;
 }
 
+cubeb_channel
+channel_label_to_cubeb_channel(UInt32 label)
+{
+  switch (label) {
+    case kAudioChannelLabel_Left:
+      return CHANNEL_FRONT_LEFT;
+    case kAudioChannelLabel_Right:
+      return CHANNEL_FRONT_RIGHT;
+    case kAudioChannelLabel_Center:
+      return CHANNEL_FRONT_CENTER;
+    case kAudioChannelLabel_LFEScreen:
+      return CHANNEL_LOW_FREQUENCY;
+    case kAudioChannelLabel_LeftSurround:
+      return CHANNEL_BACK_LEFT;
+    case kAudioChannelLabel_RightSurround:
+      return CHANNEL_BACK_RIGHT;
+    case kAudioChannelLabel_LeftCenter:
+      return CHANNEL_FRONT_LEFT_OF_CENTER;
+    case kAudioChannelLabel_RightCenter:
+      return CHANNEL_FRONT_RIGHT_OF_CENTER;
+    case kAudioChannelLabel_CenterSurround:
+      return CHANNEL_BACK_CENTER;
+    case kAudioChannelLabel_LeftSurroundDirect:
+      return CHANNEL_SIDE_LEFT;
+    case kAudioChannelLabel_RightSurroundDirect:
+      return CHANNEL_SIDE_RIGHT;
+    case kAudioChannelLabel_TopCenterSurround:
+      return CHANNEL_TOP_CENTER;
+    case kAudioChannelLabel_VerticalHeightLeft:
+      return CHANNEL_TOP_FRONT_LEFT;
+    case kAudioChannelLabel_VerticalHeightCenter:
+      return CHANNEL_TOP_FRONT_CENTER;
+    case kAudioChannelLabel_VerticalHeightRight:
+      return CHANNEL_TOP_FRONT_RIGHT;
+    case kAudioChannelLabel_TopBackLeft:
+      return CHANNEL_TOP_BACK_LEFT;
+    case kAudioChannelLabel_TopBackCenter:
+      return CHANNEL_TOP_BACK_CENTER;
+    case kAudioChannelLabel_TopBackRight:
+      return CHANNEL_TOP_BACK_RIGHT;
+    default:
+      return CHANNEL_UNKNOWN;
+  }
+}
+
+AudioChannelLabel
+cubeb_channel_to_channel_label(cubeb_channel channel)
+{
+  switch (channel) {
+    case CHANNEL_FRONT_LEFT:
+      return kAudioChannelLabel_Left;
+    case CHANNEL_FRONT_RIGHT:
+      return kAudioChannelLabel_Right;
+    case CHANNEL_FRONT_CENTER:
+      return kAudioChannelLabel_Center;
+    case CHANNEL_LOW_FREQUENCY:
+      return kAudioChannelLabel_LFEScreen;
+    case CHANNEL_BACK_LEFT:
+      return kAudioChannelLabel_LeftSurround;
+    case CHANNEL_BACK_RIGHT:
+      return kAudioChannelLabel_RightSurround;
+    case CHANNEL_FRONT_LEFT_OF_CENTER:
+      return kAudioChannelLabel_LeftCenter;
+    case CHANNEL_FRONT_RIGHT_OF_CENTER:
+      return kAudioChannelLabel_RightCenter;
+    case CHANNEL_BACK_CENTER:
+      return kAudioChannelLabel_CenterSurround;
+    case CHANNEL_SIDE_LEFT:
+      return kAudioChannelLabel_LeftSurroundDirect;
+    case CHANNEL_SIDE_RIGHT:
+      return kAudioChannelLabel_RightSurroundDirect;
+    case CHANNEL_TOP_CENTER:
+      return kAudioChannelLabel_TopCenterSurround;
+    case CHANNEL_TOP_FRONT_LEFT:
+      return kAudioChannelLabel_VerticalHeightLeft;
+    case CHANNEL_TOP_FRONT_CENTER:
+      return kAudioChannelLabel_VerticalHeightCenter;
+    case CHANNEL_TOP_FRONT_RIGHT:
+      return kAudioChannelLabel_VerticalHeightRight;
+    case CHANNEL_TOP_BACK_LEFT:
+      return kAudioChannelLabel_TopBackLeft;
+    case CHANNEL_TOP_BACK_CENTER:
+      return kAudioChannelLabel_TopBackCenter;
+    case CHANNEL_TOP_BACK_RIGHT:
+      return kAudioChannelLabel_TopBackRight;
+    default:
+      return kAudioChannelLabel_Unknown;
+  }
+}
+
 #if TARGET_OS_IPHONE
 typedef UInt32 AudioDeviceID;
 typedef UInt32 AudioObjectID;
 
 #define AudioGetCurrentHostTime mach_absolute_time
 
+#endif
+
 uint64_t
-AudioConvertHostTimeToNanos(uint64_t host_time)
+ConvertHostTimeToNanos(uint64_t host_time)
 {
   static struct mach_timebase_info timebase_info;
   static bool initialized = false;
@@ -251,27 +386,34 @@ AudioConvertHostTimeToNanos(uint64_t host_time)
   }
   return (uint64_t)answer;
 }
-#endif
 
-static int64_t
-audiotimestamp_to_latency(AudioTimeStamp const * tstamp, cubeb_stream * stream)
+static void
+audiounit_increment_active_streams(cubeb * ctx)
 {
-  if (!(tstamp->mFlags & kAudioTimeStampHostTimeValid)) {
-    return 0;
-  }
+  ctx->mutex.assert_current_thread_owns();
+  ctx->active_streams += 1;
+}
 
-  uint64_t pres = AudioConvertHostTimeToNanos(tstamp->mHostTime);
-  uint64_t now = AudioConvertHostTimeToNanos(AudioGetCurrentHostTime());
+static void
+audiounit_decrement_active_streams(cubeb * ctx)
+{
+  ctx->mutex.assert_current_thread_owns();
+  ctx->active_streams -= 1;
+}
 
-  return ((pres - now) * stream->output_desc.mSampleRate) / 1000000000LL;
+static int
+audiounit_active_streams(cubeb * ctx)
+{
+  ctx->mutex.assert_current_thread_owns();
+  return ctx->active_streams;
 }
 
 static void
-audiounit_set_global_latency(cubeb_stream * stm, uint32_t latency_frames)
+audiounit_set_global_latency(cubeb * ctx, uint32_t latency_frames)
 {
-  stm->mutex.assert_current_thread_owns();
-  assert(stm->context->active_streams == 1);
-  stm->context->global_latency_frames = latency_frames;
+  ctx->mutex.assert_current_thread_owns();
+  assert(audiounit_active_streams(ctx) == 1);
+  ctx->global_latency_frames = latency_frames;
 }
 
 static void
@@ -306,24 +448,38 @@ audiounit_render_input(cubeb_stream * stm,
                                &input_buffer_list);
 
   if (r != noErr) {
-    PRINT_ERROR_CODE("AudioUnitRender", r);
-    return r;
+    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);
   }
 
-  /* Copy input data in linear buffer. */
-  stm->input_linear_buffer->push(input_buffer_list.mBuffers[0].mData,
-                                 input_frames * stm->input_desc.mChannelsPerFrame);
-
-  LOGV("(%p) input:  buffers %d, size %d, channels %d, frames %d.",
-       stm, input_buffer_list.mNumberBuffers,
-       input_buffer_list.mBuffers[0].mDataByteSize,
-       input_buffer_list.mBuffers[0].mNumberChannels,
-       input_frames);
-
   /* 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;
 }
 
@@ -336,26 +492,15 @@ audiounit_input_callback(void * user_ptr,
                          AudioBufferList * /* bufs */)
 {
   cubeb_stream * stm = static_cast<cubeb_stream *>(user_ptr);
-  long outframes;
 
   assert(stm->input_unit != NULL);
   assert(AU_IN_BUS == bus);
 
   if (stm->shutdown) {
-    LOG("(%p) input shutdown", stm);
+    ALOG("(%p) input shutdown", stm);
     return noErr;
   }
 
-  // This happens when we're finally getting a new input callback after having
-  // switched device, we can clear the input buffer now, only keeping the data
-  // we just got.
-  if (stm->output_callback_in_a_row > stm->expected_output_callbacks_in_a_row) {
-    stm->input_linear_buffer->pop(
-        nullptr,
-        stm->input_linear_buffer->length() -
-        input_frames * stm->input_stream_params.channels);
-  }
-
   OSStatus r = audiounit_render_input(stm, flags, tstamp, bus, input_frames);
   if (r != noErr) {
     return r;
@@ -363,7 +508,6 @@ audiounit_input_callback(void * user_ptr,
 
   // Full Duplex. We'll call data_callback in the AudioUnit output callback.
   if (stm->output_unit != NULL) {
-    stm->output_callback_in_a_row = 0;
     return noErr;
   }
 
@@ -371,41 +515,59 @@ audiounit_input_callback(void * user_ptr,
      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;
-  outframes = cubeb_resampler_fill(stm->resampler,
-                                   stm->input_linear_buffer->data(),
-                                   &total_input_frames,
-                                   NULL,
-                                   0);
-  // Reset input buffer
-  stm->input_linear_buffer->clear();
-
-  if (outframes < 0 || outframes != input_frames) {
-    stm->shutdown = true;
+  long outframes = cubeb_resampler_fill(stm->resampler.get(),
+                                        stm->input_linear_buffer->data(),
+                                        &total_input_frames,
+                                        NULL,
+                                        0);
+  if (outframes < total_input_frames) {
+    OSStatus r = AudioOutputUnitStop(stm->input_unit);
+    assert(r == 0);
+    stm->state_callback(stm, stm->user_ptr, CUBEB_STATE_DRAINED);
     return noErr;
   }
 
+  // Reset input buffer
+  stm->input_linear_buffer->clear();
+
   return noErr;
 }
 
-static bool
-is_extra_input_needed(cubeb_stream * stm)
+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 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. */
-
-  /* If resampling is taking place after every output callback
-   * the input buffer expected to be empty.  Any frame left over
-   * from resampling is stored inside the resampler available to
-   * be used in next iteration as needed.
-   * BUT when noop_resampler is operating we have left over
-   * frames since it does not store anything internally. */
-  return stm->frames_read == 0 ||
-         (stm->input_linear_buffer->length() == 0 &&
-         (stm->output_callback_in_a_row > stm->expected_output_callbacks_in_a_row ||
-         stm->switching_device));
+  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
@@ -421,23 +583,32 @@ audiounit_output_callback(void * user_ptr,
 
   cubeb_stream * stm = static_cast<cubeb_stream *>(user_ptr);
 
-  stm->output_callback_in_a_row++;
+  uint64_t now = ConvertHostTimeToNanos(mach_absolute_time());
+  uint64_t audio_output_time = ConvertHostTimeToNanos(tstamp->mHostTime);
+  uint64_t output_latency_ns = audio_output_time - now;
 
-  LOGV("(%p) output: buffers %d, size %d, channels %d, frames %d.",
-       stm, outBufferList->mNumberBuffers,
-       outBufferList->mBuffers[0].mDataByteSize,
-       outBufferList->mBuffers[0].mNumberChannels, output_frames);
+  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;
 
-  long outframes = 0, input_frames = 0;
+  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) {
-    LOG("(%p) output shutdown.", stm);
+    ALOG("(%p) output shutdown.", stm);
     audiounit_make_silent(&outBufferList->mBuffers[0]);
     return noErr;
   }
 
-  stm->current_latency_frames = audiotimestamp_to_latency(tstamp, stm);
   if (stm->draining) {
     OSStatus r = AudioOutputUnitStop(stm->output_unit);
     assert(r == 0);
@@ -449,61 +620,98 @@ audiounit_output_callback(void * user_ptr,
     audiounit_make_silent(&outBufferList->mBuffers[0]);
     return noErr;
   }
+
   /* Get output buffer. */
-  output_buffer = outBufferList->mBuffers[0].mData;
+  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 (is_extra_input_needed(stm)) {
-      uint32_t min_input_frames_required = ceilf(stm->input_hw_rate / stm->output_hw_rate *
-                                                                      stm->input_buffer_frames);
-      stm->input_linear_buffer->push_silence(min_input_frames_required * stm->input_desc.mChannelsPerFrame);
-      LOG("(%p) %s pushed %u frames of input silence.", stm, stm->frames_read == 0 ? "Input hasn't started," :
-          stm->switching_device ? "Device switching," : "Drop out,", min_input_frames_required);
-    }
-    // The input buffer
+    /* 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
+    // 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. */
-  outframes = cubeb_resampler_fill(stm->resampler,
-                                   input_buffer,
-                                   input_buffer ? &input_frames : NULL,
-                                   output_buffer,
-                                   output_frames);
+  long outframes = cubeb_resampler_fill(stm->resampler.get(),
+                                        input_buffer,
+                                        input_buffer ? &input_frames : NULL,
+                                        output_buffer,
+                                        output_frames);
 
   if (input_buffer) {
-    stm->input_linear_buffer->pop(nullptr, input_frames * stm->input_desc.mChannelsPerFrame);
+    // 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) {
+  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;
   }
 
-  size_t outbpf = stm->output_desc.mBytesPerFrame;
-  stm->draining = outframes < output_frames;
+  stm->draining = (UInt32) outframes < output_frames;
   stm->frames_played = stm->frames_queued;
   stm->frames_queued += outframes;
 
-  AudioFormatFlags outaff = stm->output_desc.mFormatFlags;
-  float panning = (stm->output_desc.mChannelsPerFrame == 2) ?
-      stm->panning.load(std::memory_order_relaxed) : 0.0f;
-
   /* Post process output samples. */
   if (stm->draining) {
     /* Clear missing frames (silence) */
-    memset((uint8_t*)output_buffer + outframes * outbpf, 0, (output_frames - outframes) * outbpf);
+    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);
   }
-  /* Pan stereo. */
-  if (panning != 0.0f) {
-    if (outaff & kAudioFormatFlagIsFloat) {
-      cubeb_pan_stereo_buffer_float((float*)output_buffer, outframes, panning);
-    } else if (outaff & kAudioFormatFlagIsSignedInteger) {
-      cubeb_pan_stereo_buffer_int((short*)output_buffer, outframes, panning);
-    }
+
+  /* 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;
 }
 
@@ -511,25 +719,11 @@ extern "C" {
 int
 audiounit_init(cubeb ** context, char const * /* context_name */)
 {
-  cubeb * ctx;
-
-  *context = NULL;
-
-  ctx = (cubeb *)calloc(1, sizeof(cubeb));
-  assert(ctx);
-  // Placement new to call the ctors of cubeb members.
-  new (ctx) cubeb();
-
-  ctx->ops = &audiounit_ops;
-
-  ctx->active_streams = 0;
-
-  ctx->limit_streams = kCFCoreFoundationVersionNumber < kCFCoreFoundationVersionNumber10_7;
 #if !TARGET_OS_IPHONE
   cubeb_set_coreaudio_notification_runloop();
 #endif
 
-  *context = ctx;
+  *context = new cubeb;
 
   return CUBEB_OK;
 }
@@ -542,146 +736,233 @@ audiounit_get_backend_id(cubeb * /* ctx */)
 }
 
 #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_get_output_device_id(AudioDeviceID * device_id)
+audiounit_set_device_info(cubeb_stream * stm, AudioDeviceID id, io_side side)
 {
-  UInt32 size;
-  OSStatus r;
-  AudioObjectPropertyAddress output_device_address = {
-    kAudioHardwarePropertyDefaultOutputDevice,
-    kAudioObjectPropertyScopeGlobal,
-    kAudioObjectPropertyElementMaster
-  };
+  assert(stm);
 
-  size = sizeof(*device_id);
+  device_info * info = nullptr;
+  cubeb_device_type type = CUBEB_DEVICE_TYPE_UNKNOWN;
 
-  r = AudioObjectGetPropertyData(kAudioObjectSystemObject,
-                                 &output_device_address,
-                                 0,
-                                 NULL,
-                                 &size,
-                                 device_id);
-  if (r != noErr) {
-    PRINT_ERROR_CODE("output_device_id", r);
-    return CUBEB_ERROR;
+  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;
 
-  return CUBEB_OK;
-}
-
-static int
-audiounit_get_input_device_id(AudioDeviceID * device_id)
-{
-  UInt32 size;
-  OSStatus r;
-  AudioObjectPropertyAddress input_device_address = {
-    kAudioHardwarePropertyDefaultInputDevice,
-    kAudioObjectPropertyScopeGlobal,
-    kAudioObjectPropertyElementMaster
-  };
-
-  size = sizeof(*device_id);
+  if (side == io_side::INPUT) {
+    info->flags |= DEV_INPUT;
+  } else if (side == io_side::OUTPUT) {
+    info->flags |= DEV_OUTPUT;
+  }
 
-  r = AudioObjectGetPropertyData(kAudioObjectSystemObject,
-                                 &input_device_address,
-                                 0,
-                                 NULL,
-                                 &size,
-                                 device_id);
-  if (r != noErr) {
+  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_stream_get_volume(cubeb_stream * stm, float * volume);
-static int audiounit_stream_set_volume(cubeb_stream * stm, float volume);
-static int audiounit_uninstall_device_changed_callback(cubeb_stream * stm);
 
 static int
-audiounit_reinit_stream(cubeb_stream * stm)
+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 the device changed callback", stm);
+    LOG("(%p) Could not uninstall all device change listeners.", stm);
   }
 
   {
     auto_lock lock(stm->mutex);
     float volume = 0.0;
-    int vol_rv = audiounit_stream_get_volume(stm, &volume);
+    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);
-      return CUBEB_ERROR;
+      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);
     }
 
-    // Reset input frames to force new stream pre-buffer
-    // silence if needed, check `is_extra_input_needed()`
-    stm->frames_read = 0;
-
     // If the stream was running, start it again.
     if (!stm->shutdown) {
-      audiounit_stream_start_internal(stm);
+      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,
+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, %d events.", stm, address_count);
+  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[%d] - mSelector == kAudioHardwarePropertyDefaultOutputDevice", i);
-          // Allow restart to choose the new default
-          stm->output_device = nullptr;
+          LOG("Event[%u] - mSelector == kAudioHardwarePropertyDefaultOutputDevice for id=%d", (unsigned int) i, id);
         }
         break;
       case kAudioHardwarePropertyDefaultInputDevice: {
-          LOG("Event[%d] - mSelector == kAudioHardwarePropertyDefaultInputDevice", i);
-          // Allow restart to choose the new default
-          stm->input_device = nullptr;
+          LOG("Event[%u] - mSelector == kAudioHardwarePropertyDefaultInputDevice for id=%d", (unsigned int) i, id);
         }
       break;
       case kAudioDevicePropertyDeviceIsAlive: {
-          LOG("Event[%d] - mSelector == kAudioDevicePropertyDeviceIsAlive", i);
+          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->is_default_input) {
+          if (stm->input_device.flags & DEV_SYSTEM_DEFAULT) {
             LOG("It's the default input device, ignore the event");
+            stm->switching_device = false;
             return noErr;
           }
-          // Allow restart to choose the new default. Event register only for input.
-          stm->input_device = nullptr;
         }
         break;
       case kAudioDevicePropertyDataSource: {
-          LOG("Event[%d] - mSelector == kAudioHardwarePropertyDataSource", i);
-          return noErr;
+          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:
@@ -689,7 +970,7 @@ audiounit_property_listener_callback(AudioObjectID /* id */, UInt32 address_coun
     case kAudioDevicePropertyDeviceIsAlive:
       /* fall through */
     case kAudioDevicePropertyDataSource: {
-        auto_lock lock(stm->mutex);
+        auto_lock dev_cb_lock(stm->device_changed_callback_lock);
         if (stm->device_changed_callback) {
           stm->device_changed_callback(stm->user_ptr);
         }
@@ -698,99 +979,77 @@ audiounit_property_listener_callback(AudioObjectID /* id */, UInt32 address_coun
     }
   }
 
-  // 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 (audiounit_reinit_stream(stm) != CUBEB_OK) {
-      stm->state_callback(stm, stm->user_ptr, CUBEB_STATE_STOPPED);
-      LOG("(%p) Could not reopen the stream after switching.", stm);
-    }
-    stm->switching_device = false;
-  });
+  audiounit_reinit_stream_async(stm, switch_side);
 
   return noErr;
 }
 
 OSStatus
-audiounit_add_listener(cubeb_stream * stm, AudioDeviceID id, AudioObjectPropertySelector selector,
-    AudioObjectPropertyScope scope, AudioObjectPropertyListenerProc listener)
+audiounit_add_listener(const property_listener * listener)
 {
-  AudioObjectPropertyAddress address = {
-      selector,
-      scope,
-      kAudioObjectPropertyElementMaster
-  };
-
-  return AudioObjectAddPropertyListener(id, &address, listener, stm);
+  assert(listener);
+  return AudioObjectAddPropertyListener(listener->device_id,
+                                        listener->property_address,
+                                        listener->callback,
+                                        listener->stream);
 }
 
 OSStatus
-audiounit_remove_listener(cubeb_stream * stm, AudioDeviceID id,
-                          AudioObjectPropertySelector selector,
-                          AudioObjectPropertyScope scope,
-                          AudioObjectPropertyListenerProc listener)
-{
-  AudioObjectPropertyAddress address = {
-      selector,
-      scope,
-      kAudioObjectPropertyElementMaster
-  };
-
-  return AudioObjectRemovePropertyListener(id, &address, listener, stm);
+audiounit_remove_listener(const property_listener * listener)
+{
+  assert(listener);
+  return AudioObjectRemovePropertyListener(listener->device_id,
+                                           listener->property_address,
+                                           listener->callback,
+                                           listener->stream);
 }
 
-static AudioObjectID audiounit_get_default_device_id(cubeb_device_type type);
-
 static int
 audiounit_install_device_changed_callback(cubeb_stream * stm)
 {
-  OSStatus r;
+  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. */
-    AudioDeviceID output_dev_id;
-    r = audiounit_get_output_device_id(&output_dev_id);
-    if (r != noErr) {
-      return CUBEB_ERROR;
-    }
-
-    r = audiounit_add_listener(stm, output_dev_id, kAudioDevicePropertyDataSource,
-        kAudioDevicePropertyScopeOutput, &audiounit_property_listener_callback);
-    if (r != noErr) {
-      PRINT_ERROR_CODE("AudioObjectAddPropertyListener/output/kAudioDevicePropertyDataSource", r);
-      return CUBEB_ERROR;
+    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. */
-    AudioDeviceID input_dev_id;
-    r = audiounit_get_input_device_id(&input_dev_id);
-    if (r != noErr) {
-      return CUBEB_ERROR;
-    }
-
-    r = audiounit_add_listener(stm, input_dev_id, kAudioDevicePropertyDataSource,
-        kAudioDevicePropertyScopeInput, &audiounit_property_listener_callback);
-    if (r != noErr) {
-      PRINT_ERROR_CODE("AudioObjectAddPropertyListener/input/kAudioDevicePropertyDataSource", r);
-      return CUBEB_ERROR;
+    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. */
-    AudioDeviceID dev = stm->input_device ? reinterpret_cast<intptr_t>(stm->input_device) :
-                                            audiounit_get_default_device_id(CUBEB_DEVICE_TYPE_INPUT);
-    r = audiounit_add_listener(stm, dev, kAudioDevicePropertyDeviceIsAlive,
-        kAudioObjectPropertyScopeGlobal, &audiounit_property_listener_callback);
-    if (r != noErr) {
-      PRINT_ERROR_CODE("AudioObjectAddPropertyListener/input/kAudioDevicePropertyDeviceIsAlive", r);
-      return CUBEB_ERROR;
+    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 CUBEB_OK;
+  return r;
 }
 
 static int
@@ -803,9 +1062,12 @@ audiounit_install_system_changed_callback(cubeb_stream * stm)
      * 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. */
-    r = audiounit_add_listener(stm, kAudioObjectSystemObject, kAudioHardwarePropertyDefaultOutputDevice,
-                               kAudioObjectPropertyScopeGlobal, &audiounit_property_listener_callback);
+    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;
     }
@@ -813,9 +1075,12 @@ audiounit_install_system_changed_callback(cubeb_stream * stm)
 
   if (stm->input_unit) {
     /* This event will notify us when the default input device changes. */
-    r = audiounit_add_listener(stm, kAudioObjectSystemObject, kAudioHardwarePropertyDefaultInputDevice,
-                               kAudioObjectPropertyScopeGlobal, &audiounit_property_listener_callback);
+    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;
     }
@@ -827,36 +1092,38 @@ audiounit_install_system_changed_callback(cubeb_stream * stm)
 static int
 audiounit_uninstall_device_changed_callback(cubeb_stream * stm)
 {
-  OSStatus r;
-
-  if (stm->output_unit) {
-    AudioDeviceID output_dev_id;
-    r = audiounit_get_output_device_id(&output_dev_id);
-    if (r != noErr) {
-      return CUBEB_ERROR;
-    }
+  OSStatus rv;
+  // Failing to uninstall listeners is not a fatal error.
+  int r = CUBEB_OK;
 
-    r = audiounit_remove_listener(stm, output_dev_id, kAudioDevicePropertyDataSource,
-        kAudioDevicePropertyScopeOutput, &audiounit_property_listener_callback);
-    if (r != noErr) {
-      return CUBEB_ERROR;
+  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_unit) {
-    AudioDeviceID input_dev_id;
-    r = audiounit_get_input_device_id(&input_dev_id);
-    if (r != noErr) {
-      return CUBEB_ERROR;
+  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();
+  }
 
-    r = audiounit_remove_listener(stm, input_dev_id, kAudioDevicePropertyDataSource,
-        kAudioDevicePropertyScopeInput, &audiounit_property_listener_callback);
-    if (r != noErr) {
-      return CUBEB_ERROR;
+  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 CUBEB_OK;
+
+  return r;
 }
 
 static int
@@ -864,20 +1131,20 @@ audiounit_uninstall_system_changed_callback(cubeb_stream * stm)
 {
   OSStatus r;
 
-  if (stm->output_unit) {
-    r = audiounit_remove_listener(stm, kAudioObjectSystemObject, kAudioHardwarePropertyDefaultOutputDevice,
-                                  kAudioObjectPropertyScopeGlobal, &audiounit_property_listener_callback);
+  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->input_unit) {
-    r = audiounit_remove_listener(stm, kAudioObjectSystemObject, kAudioHardwarePropertyDefaultInputDevice,
-                                  kAudioObjectPropertyScopeGlobal, &audiounit_property_listener_callback);
+  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;
 }
@@ -895,7 +1162,8 @@ audiounit_get_acceptable_latency_range(AudioValueRange * latency_range)
     kAudioObjectPropertyElementMaster
   };
 
-  if (audiounit_get_output_device_id(&output_device_id) != CUBEB_OK) {
+  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;
   }
@@ -910,7 +1178,7 @@ audiounit_get_acceptable_latency_range(AudioValueRange * latency_range)
                                  &size,
                                  latency_range);
   if (r != noErr) {
-    PRINT_ERROR_CODE("AudioObjectGetPropertyData/buffer size range", r);
+    LOG("AudioObjectGetPropertyData/buffer size range rv=%d", r);
     return CUBEB_ERROR;
   }
 
@@ -921,20 +1189,19 @@ audiounit_get_acceptable_latency_range(AudioValueRange * latency_range)
 static AudioObjectID
 audiounit_get_default_device_id(cubeb_device_type type)
 {
-  AudioObjectPropertyAddress adr = { 0, kAudioObjectPropertyScopeGlobal, kAudioObjectPropertyElementMaster };
-  AudioDeviceID devid;
-  UInt32 size;
-
+  const AudioObjectPropertyAddress * adr;
   if (type == CUBEB_DEVICE_TYPE_OUTPUT) {
-    adr.mSelector = kAudioHardwarePropertyDefaultOutputDevice;
+    adr = &DEFAULT_OUTPUT_DEVICE_PROPERTY_ADDRESS;
   } else if (type == CUBEB_DEVICE_TYPE_INPUT) {
-    adr.mSelector = kAudioHardwarePropertyDefaultInputDevice;
+    adr = &DEFAULT_INPUT_DEVICE_PROPERTY_ADDRESS;
   } else {
     return kAudioObjectUnknown;
   }
 
-  size = sizeof(AudioDeviceID);
-  if (AudioObjectGetPropertyData(kAudioObjectSystemObject, &adr, 0, NULL, &size, &devid) != noErr) {
+  AudioDeviceID devid;
+  UInt32 size = sizeof(AudioDeviceID);
+  if (AudioObjectGetPropertyData(kAudioObjectSystemObject,
+                                 adr, 0, NULL, &size, &devid) != noErr) {
     return kAudioObjectUnknown;
   }
 
@@ -960,7 +1227,8 @@ audiounit_get_max_channel_count(cubeb * ctx, uint32_t * max_channels)
 
   assert(ctx && max_channels);
 
-  if (audiounit_get_output_device_id(&output_device_id) != CUBEB_OK) {
+  output_device_id = audiounit_get_default_device_id(CUBEB_DEVICE_TYPE_OUTPUT);
+  if (output_device_id == kAudioObjectUnknown) {
     return CUBEB_ERROR;
   }
 
@@ -973,7 +1241,7 @@ audiounit_get_max_channel_count(cubeb * ctx, uint32_t * max_channels)
                                  &size,
                                  &stream_format);
   if (r != noErr) {
-    PRINT_ERROR_CODE("AudioObjectPropertyAddress/StreamFormat", r);
+    LOG("AudioObjectPropertyAddress/StreamFormat rv=%d", r);
     return CUBEB_ERROR;
   }
 
@@ -997,7 +1265,7 @@ audiounit_get_min_latency(cubeb * /* ctx */,
     return CUBEB_ERROR;
   }
 
-  *latency_frames = std::max<uint32_t>(latency_range.mMinimum,
+  *latency_frames = max<uint32_t>(latency_range.mMinimum,
                                        SAFE_MIN_LATENCY_FRAMES);
 #endif
 
@@ -1021,7 +1289,8 @@ audiounit_get_preferred_sample_rate(cubeb * /* ctx */, uint32_t * rate)
     kAudioObjectPropertyElementMaster
   };
 
-  if (audiounit_get_output_device_id(&output_device_id) != CUBEB_OK) {
+  output_device_id = audiounit_get_default_device_id(CUBEB_DEVICE_TYPE_OUTPUT);
+  if (output_device_id == kAudioObjectUnknown) {
     return CUBEB_ERROR;
   }
 
@@ -1042,24 +1311,133 @@ audiounit_get_preferred_sample_rate(cubeb * /* ctx */, uint32_t * rate)
   return CUBEB_OK;
 }
 
-static OSStatus audiounit_remove_device_listener(cubeb * context);
+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)
 {
-  // Disabling this assert for bug 1083664 -- we seem to leak a stream
-  // assert(ctx->active_streams == 0);
-
   {
     auto_lock lock(ctx->mutex);
+
+    // Disabling this assert for bug 1083664 -- we seem to leak a stream
+    // assert(ctx->active_streams == 0);
+    if (audiounit_active_streams(ctx) > 0) {
+      LOG("(%p) API misuse, %d streams active when context destroyed!", ctx, audiounit_active_streams(ctx));
+    }
+
     /* Unregister the callback if necessary. */
-    if(ctx->collection_changed_callback) {
-      audiounit_remove_device_listener(ctx);
+    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);
     }
   }
 
-  ctx->~cubeb();
-  free(ctx);
+  dispatch_release(ctx->serial_queue);
+
+  delete ctx;
 }
 
 static void audiounit_stream_destroy(cubeb_stream * stm);
@@ -1105,29 +1483,527 @@ audio_stream_desc_init(AudioStreamBasicDescription * ss,
   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_create_unit(AudioUnit * unit,
-                      bool is_input,
-                      const cubeb_stream_params * /* stream_params */,
-                      cubeb_devid device)
+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;
-  UInt32 enable;
-  AudioDeviceID devid;
   OSStatus rv;
 
   desc.componentType = kAudioUnitType_Output;
 #if TARGET_OS_IPHONE
-  bool use_default_output = false;
   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.
-  bool use_default_output = device == NULL && !is_input;
-  if (use_default_output) {
+  if ((device->flags & DEV_SYSTEM_DEFAULT) &&
+      (device->flags & DEV_OUTPUT)) {
     desc.componentSubType = kAudioUnitSubType_DefaultOutput;
   } else {
     desc.componentSubType = kAudioUnitSubType_HALOutput;
@@ -1144,96 +2020,118 @@ audiounit_create_unit(AudioUnit * unit,
 
   rv = AudioComponentInstanceNew(comp, unit);
   if (rv != noErr) {
-    PRINT_ERROR_CODE("AudioComponentInstanceNew", rv);
+    LOG("AudioComponentInstanceNew rv=%d", rv);
     return CUBEB_ERROR;
   }
+  return CUBEB_OK;
+}
 
-  if (!use_default_output) {
-    enable = 1;
-    rv = AudioUnitSetProperty(*unit, kAudioOutputUnitProperty_EnableIO,
-                              is_input ? kAudioUnitScope_Input : kAudioUnitScope_Output,
-                              is_input ? AU_IN_BUS : AU_OUT_BUS, &enable, sizeof(UInt32));
-    if (rv != noErr) {
-      PRINT_ERROR_CODE("AudioUnitSetProperty/kAudioOutputUnitProperty_EnableIO", rv);
-      return CUBEB_ERROR;
-    }
-
-    enable = 0;
-    rv = AudioUnitSetProperty(*unit, kAudioOutputUnitProperty_EnableIO,
-                              is_input ? kAudioUnitScope_Output : kAudioUnitScope_Input,
-                              is_input ? AU_OUT_BUS : AU_IN_BUS, &enable, sizeof(UInt32));
-    if (rv != noErr) {
-      PRINT_ERROR_CODE("AudioUnitSetProperty/kAudioOutputUnitProperty_EnableIO", rv);
-      return CUBEB_ERROR;
-    }
+enum enable_state {
+  DISABLE,
+  ENABLE,
+};
 
-    if (device == NULL) {
-      assert(is_input);
-      devid = audiounit_get_default_device_id(CUBEB_DEVICE_TYPE_INPUT);
-    } else {
-      devid = reinterpret_cast<intptr_t>(device);
-    }
-    rv = AudioUnitSetProperty(*unit, kAudioOutputUnitProperty_CurrentDevice,
-                              kAudioUnitScope_Global,
-                              is_input ? AU_IN_BUS : AU_OUT_BUS,
-                              &devid, sizeof(AudioDeviceID));
-    if (rv != noErr) {
-      PRINT_ERROR_CODE("AudioUnitSetProperty/kAudioOutputUnitProperty_CurrentDevice", rv);
-      return CUBEB_ERROR;
-    }
+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_init_input_linear_buffer(cubeb_stream * stream, uint32_t capacity)
+audiounit_create_unit(AudioUnit * unit, device_info * device)
 {
-  if (stream->input_desc.mFormatFlags & kAudioFormatFlagIsSignedInteger) {
-    stream->input_linear_buffer = new auto_array_wrapper(
-        new auto_array<short>(capacity *
-                              stream->input_buffer_frames *
-                              stream->input_desc.mChannelsPerFrame) );
-  } else {
-    stream->input_linear_buffer = new auto_array_wrapper(
-        new auto_array<float>(capacity *
-                              stream->input_buffer_frames *
-                              stream->input_desc.mChannelsPerFrame) );
+  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 (!stream->input_linear_buffer) {
-    return CUBEB_ERROR;
+  if ((device->flags & DEV_SYSTEM_DEFAULT) &&
+      (device->flags & DEV_OUTPUT)) {
+    return CUBEB_OK;
   }
 
-  assert(stream->input_linear_buffer->length() == 0);
 
-  // Pre-buffer silence if needed
-  if (capacity != 1) {
-    size_t silence_size = stream->input_buffer_frames *
-                          stream->input_desc.mChannelsPerFrame;
-    stream->input_linear_buffer->push_silence(silence_size);
+  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);
+  }
 
-    assert(stream->input_linear_buffer->length() == silence_size);
+  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 void
-audiounit_destroy_input_linear_buffer(cubeb_stream * stream)
+static int
+audiounit_init_input_linear_buffer(cubeb_stream * stream, uint32_t capacity)
 {
-  delete stream->input_linear_buffer;
+  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(stm->context->active_streams > 0);
-  if (stm->context->active_streams == 1) {
-    return std::max(std::min<uint32_t>(latency_frames, SAFE_MAX_LATENCY_FRAMES),
+  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
@@ -1248,11 +2146,11 @@ audiounit_clamp_latency(cubeb_stream * stm, uint32_t latency_frames)
                             &output_buffer_size,
                             &size);
     if (r != noErr) {
-      PRINT_ERROR_CODE("AudioUnitGetProperty/output/kAudioDevicePropertyBufferFrameSize", r);
+      LOG("AudioUnitGetProperty/output/kAudioDevicePropertyBufferFrameSize rv=%d", r);
       return 0;
     }
 
-    output_buffer_size = std::max(std::min<uint32_t>(output_buffer_size, SAFE_MAX_LATENCY_FRAMES),
+    output_buffer_size = max(min<uint32_t>(output_buffer_size, SAFE_MAX_LATENCY_FRAMES),
                                   SAFE_MIN_LATENCY_FRAMES);
   }
 
@@ -1265,18 +2163,18 @@ audiounit_clamp_latency(cubeb_stream * stm, uint32_t latency_frames)
                             &input_buffer_size,
                             &size);
     if (r != noErr) {
-      PRINT_ERROR_CODE("AudioUnitGetProperty/input/kAudioDevicePropertyBufferFrameSize", r);
+      LOG("AudioUnitGetProperty/input/kAudioDevicePropertyBufferFrameSize rv=%d", r);
       return 0;
     }
 
-    input_buffer_size = std::max(std::min<uint32_t>(input_buffer_size, SAFE_MAX_LATENCY_FRAMES),
+    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 = std::min<uint32_t>(input_buffer_size, output_buffer_size);
+    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) {
@@ -1285,7 +2183,7 @@ audiounit_clamp_latency(cubeb_stream * stm, uint32_t latency_frames)
     upper_latency_limit = SAFE_MAX_LATENCY_FRAMES;
   }
 
-  return std::max(std::min<uint32_t>(latency_frames, upper_latency_limit),
+  return max(min<uint32_t>(latency_frames, upper_latency_limit),
                   SAFE_MIN_LATENCY_FRAMES);
 }
 
@@ -1300,18 +2198,18 @@ audiounit_clamp_latency(cubeb_stream * stm, uint32_t latency_frames)
 static void
 buffer_size_changed_callback(void * inClientData,
                              AudioUnit inUnit,
-                             AudioUnitPropertyID	inPropertyID,
-                             AudioUnitScope		inScope,
-                             AudioUnitElement	inElement)
+                             AudioUnitPropertyID inPropertyID,
+                             AudioUnitScope inScope,
+                             AudioUnitElement inElement)
 {
   cubeb_stream * stm = (cubeb_stream *)inClientData;
 
   AudioUnit au = inUnit;
   AudioUnitScope au_scope = kAudioUnitScope_Input;
   AudioUnitElement au_element = inElement;
-  const char * au_type = "output";
+  char const * au_type = "output";
 
-  if (au == stm->input_unit) {
+  if (AU_IN_BUS == inElement) {
     au_scope = kAudioUnitScope_Output;
     au_type = "input";
   }
@@ -1342,24 +2240,17 @@ buffer_size_changed_callback(void * inClientData,
   }
 }
 
-enum set_buffer_size_side {
-  INPUT,
-  OUTPUT,
-};
-
 static int
-audiounit_set_buffer_size(cubeb_stream * stm, uint32_t new_size_frames, set_buffer_size_side set_side)
+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;
-  const char * au_type = "output";
 
-  if (set_side == INPUT) {
+  if (side == io_side::INPUT) {
     au = stm->input_unit;
     au_scope = kAudioUnitScope_Output;
     au_element = AU_IN_BUS;
-    au_type = "input";
   }
 
   uint32_t buffer_frames = 0;
@@ -1371,16 +2262,12 @@ audiounit_set_buffer_size(cubeb_stream * stm, uint32_t new_size_frames, set_buff
                                &buffer_frames,
                                &size);
   if (r != noErr) {
-    if (set_side == INPUT) {
-      PRINT_ERROR_CODE("AudioUnitGetProperty/input/kAudioDevicePropertyBufferFrameSize", r);
-    } else {
-      PRINT_ERROR_CODE("AudioUnitGetProperty/output/kAudioDevicePropertyBufferFrameSize", r);
-    }
+    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, au_type, buffer_frames);
+    LOG("(%p) No need to update %s buffer size already %u frames", stm, to_string(side), buffer_frames);
     return CUBEB_OK;
   }
 
@@ -1389,11 +2276,7 @@ audiounit_set_buffer_size(cubeb_stream * stm, uint32_t new_size_frames, set_buff
                                    buffer_size_changed_callback,
                                    stm);
   if (r != noErr) {
-    if (set_side == INPUT) {
-      PRINT_ERROR_CODE("AudioUnitAddPropertyListener/input/kAudioDevicePropertyBufferFrameSize", r);
-    } else {
-      PRINT_ERROR_CODE("AudioUnitAddPropertyListener/output/kAudioDevicePropertyBufferFrameSize", r);
-    }
+    LOG("AudioUnitAddPropertyListener/%s/kAudioDevicePropertyBufferFrameSize rv=%d", to_string(side), r);
     return CUBEB_ERROR;
   }
 
@@ -1406,22 +2289,14 @@ audiounit_set_buffer_size(cubeb_stream * stm, uint32_t new_size_frames, set_buff
                            &new_size_frames,
                            sizeof(new_size_frames));
   if (r != noErr) {
-    if (set_side == INPUT) {
-      PRINT_ERROR_CODE("AudioUnitSetProperty/input/kAudioDevicePropertyBufferFrameSize", r);
-    } else {
-      PRINT_ERROR_CODE("AudioUnitSetProperty/output/kAudioDevicePropertyBufferFrameSize", r);
-    }
+    LOG("AudioUnitSetProperty/%s/kAudioDevicePropertyBufferFrameSize rv=%d", to_string(side), r);
 
     r = AudioUnitRemovePropertyListenerWithUserData(au,
                                                     kAudioDevicePropertyBufferFrameSize,
                                                     buffer_size_changed_callback,
                                                     stm);
     if (r != noErr) {
-      if (set_side == INPUT) {
-        PRINT_ERROR_CODE("AudioUnitAddPropertyListener/input/kAudioDevicePropertyBufferFrameSize", r);
-      } else {
-        PRINT_ERROR_CODE("AudioUnitAddPropertyListener/output/kAudioDevicePropertyBufferFrameSize", r);
-      }
+      LOG("AudioUnitAddPropertyListener/%s/kAudioDevicePropertyBufferFrameSize rv=%d", to_string(side), r);
     }
 
     return CUBEB_ERROR;
@@ -1443,11 +2318,7 @@ audiounit_set_buffer_size(cubeb_stream * stm, uint32_t new_size_frames, set_buff
                                                   buffer_size_changed_callback,
                                                   stm);
   if (r != noErr) {
-    if (set_side == INPUT) {
-      PRINT_ERROR_CODE("AudioUnitAddPropertyListener/input/kAudioDevicePropertyBufferFrameSize", r);
-    } else {
-      PRINT_ERROR_CODE("AudioUnitAddPropertyListener/output/kAudioDevicePropertyBufferFrameSize", r);
-    }
+    LOG("AudioUnitAddPropertyListener/%s/kAudioDevicePropertyBufferFrameSize rv=%d", to_string(side), r);
     return CUBEB_ERROR;
   }
 
@@ -1456,13 +2327,15 @@ audiounit_set_buffer_size(cubeb_stream * stm, uint32_t new_size_frames, set_buff
     return CUBEB_ERROR;
   }
 
-  LOG("(%p) %s buffer size changed to %u frames.", stm, au_type, new_size_frames);
+  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;
@@ -1481,7 +2354,7 @@ audiounit_configure_input(cubeb_stream * stm)
                            &input_hw_desc,
                            &size);
   if (r != noErr) {
-    PRINT_ERROR_CODE("AudioUnitGetProperty/input/kAudioUnitProperty_StreamFormat", r);
+    LOG("AudioUnitGetProperty/input/kAudioUnitProperty_StreamFormat rv=%d", r);
     return CUBEB_ERROR;
   }
   stm->input_hw_rate = input_hw_desc.mSampleRate;
@@ -1495,8 +2368,7 @@ audiounit_configure_input(cubeb_stream * stm)
   }
 
   // Use latency to set buffer size
-  stm->input_buffer_frames = stm->latency_frames;
-  r = audiounit_set_buffer_size(stm, stm->input_buffer_frames, INPUT);
+  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;
@@ -1514,7 +2386,7 @@ audiounit_configure_input(cubeb_stream * stm)
                            &src_desc,
                            sizeof(AudioStreamBasicDescription));
   if (r != noErr) {
-    PRINT_ERROR_CODE("AudioUnitSetProperty/input/kAudioUnitProperty_StreamFormat", r);
+    LOG("AudioUnitSetProperty/input/kAudioUnitProperty_StreamFormat rv=%d", r);
     return CUBEB_ERROR;
   }
 
@@ -1523,10 +2395,10 @@ audiounit_configure_input(cubeb_stream * stm)
                            kAudioUnitProperty_MaximumFramesPerSlice,
                            kAudioUnitScope_Global,
                            AU_IN_BUS,
-                           &stm->input_buffer_frames,
+                           &stm->latency_frames,
                            sizeof(UInt32));
   if (r != noErr) {
-    PRINT_ERROR_CODE("AudioUnitSetProperty/input/kAudioUnitProperty_MaximumFramesPerSlice", r);
+    LOG("AudioUnitSetProperty/input/kAudioUnitProperty_MaximumFramesPerSlice rv=%d", r);
     return CUBEB_ERROR;
   }
 
@@ -1540,7 +2412,6 @@ audiounit_configure_input(cubeb_stream * stm)
     return CUBEB_ERROR;
   }
 
-  assert(stm->input_unit != NULL);
   aurcbs_in.inputProc = audiounit_input_callback;
   aurcbs_in.inputProcRefCon = stm;
 
@@ -1551,9 +2422,12 @@ audiounit_configure_input(cubeb_stream * stm)
                            &aurcbs_in,
                            sizeof(aurcbs_in));
   if (r != noErr) {
-    PRINT_ERROR_CODE("AudioUnitSetProperty/input/kAudioOutputUnitProperty_SetInputCallback", r);
+    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;
@@ -1562,6 +2436,8 @@ audiounit_configure_input(cubeb_stream * stm)
 static int
 audiounit_configure_output(cubeb_stream * stm)
 {
+  assert(stm && stm->output_unit);
+
   int r;
   AURenderCallbackStruct aurcbs_out;
   UInt32 size;
@@ -1588,11 +2464,30 @@ audiounit_configure_output(cubeb_stream * stm)
                            &output_hw_desc,
                            &size);
   if (r != noErr) {
-    PRINT_ERROR_CODE("AudioUnitGetProperty/output/tkAudioUnitProperty_StreamFormat", r);
+    LOG("AudioUnitGetProperty/output/kAudioUnitProperty_StreamFormat rv=%d", r);
     return CUBEB_ERROR;
   }
   stm->output_hw_rate = output_hw_desc.mSampleRate;
   LOG("(%p) Output device sampling rate: %.2f", stm, output_hw_desc.mSampleRate);
+  stm->context->channels = output_hw_desc.mChannelsPerFrame;
+
+  // Set the input layout to match the output device layout.
+  audiounit_layout_init(stm, io_side::OUTPUT);
+  if (stm->context->channels != stm->output_stream_params.channels ||
+      stm->context->layout != stm->output_stream_params.layout) {
+    LOG("Incompatible channel layouts detected, setting up remixer");
+    audiounit_init_mixer(stm);
+    // We will be remixing the data before it reaches the output device.
+    // We need to adjust the number of channels and other
+    // AudioStreamDescription details.
+    stm->output_desc.mChannelsPerFrame = stm->context->channels;
+    stm->output_desc.mBytesPerFrame = (stm->output_desc.mBitsPerChannel / 8) *
+                                      stm->output_desc.mChannelsPerFrame;
+    stm->output_desc.mBytesPerPacket =
+      stm->output_desc.mBytesPerFrame * stm->output_desc.mFramesPerPacket;
+  } else {
+    stm->mixer = nullptr;
+  }
 
   r = AudioUnitSetProperty(stm->output_unit,
                            kAudioUnitProperty_StreamFormat,
@@ -1601,11 +2496,11 @@ audiounit_configure_output(cubeb_stream * stm)
                            &stm->output_desc,
                            sizeof(AudioStreamBasicDescription));
   if (r != noErr) {
-    PRINT_ERROR_CODE("AudioUnitSetProperty/output/kAudioUnitProperty_StreamFormat", r);
+    LOG("AudioUnitSetProperty/output/kAudioUnitProperty_StreamFormat rv=%d", r);
     return CUBEB_ERROR;
   }
 
-  r = audiounit_set_buffer_size(stm, stm->latency_frames, OUTPUT);
+  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;
@@ -1619,11 +2514,10 @@ audiounit_configure_output(cubeb_stream * stm)
                            &stm->latency_frames,
                            sizeof(UInt32));
   if (r != noErr) {
-    PRINT_ERROR_CODE("AudioUnitSetProperty/output/kAudioUnitProperty_MaximumFramesPerSlice", r);
+    LOG("AudioUnitSetProperty/output/kAudioUnitProperty_MaximumFramesPerSlice rv=%d", r);
     return CUBEB_ERROR;
   }
 
-  assert(stm->output_unit != NULL);
   aurcbs_out.inputProc = audiounit_output_callback;
   aurcbs_out.inputProcRefCon = stm;
   r = AudioUnitSetProperty(stm->output_unit,
@@ -1633,10 +2527,12 @@ audiounit_configure_output(cubeb_stream * stm)
                            &aurcbs_out,
                            sizeof(aurcbs_out));
   if (r != noErr) {
-    PRINT_ERROR_CODE("AudioUnitSetProperty/output/kAudioUnitProperty_SetRenderCallback", r);
+    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;
 }
@@ -1646,11 +2542,37 @@ 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, true,
-                              &stm->input_stream_params,
-                              stm->input_device);
+    r = audiounit_create_unit(&stm->input_unit, &in_dev_info);
     if (r != CUBEB_OK) {
       LOG("(%p) AudioUnit creation for input failed.", stm);
       return r;
@@ -1658,9 +2580,7 @@ audiounit_setup_stream(cubeb_stream * stm)
   }
 
   if (has_output(stm)) {
-    r = audiounit_create_unit(&stm->output_unit, false,
-                              &stm->output_stream_params,
-                              stm->output_device);
+    r = audiounit_create_unit(&stm->output_unit, &out_dev_info);
     if (r != CUBEB_OK) {
       LOG("(%p) AudioUnit creation for output failed.", stm);
       return r;
@@ -1668,20 +2588,20 @@ audiounit_setup_stream(cubeb_stream * stm)
   }
 
   /* Latency cannot change if another stream is operating in parallel. In this case
-  * latecy is set to the other stream value. */
-  if (stm->context->active_streams > 1) {
+   * 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. */
+     * synthetize the clock from the callbacks, and we want the clock to update
+     * often. */
     stm->latency_frames = audiounit_clamp_latency(stm, stm->latency_frames);
-    assert(stm->latency_frames); // Ungly error check
-    audiounit_set_global_latency(stm, stm->latency_frames);
+    assert(stm->latency_frames); // Ugly error check
+    audiounit_set_global_latency(stm->context, stm->latency_frames);
   }
 
-  /* Setup Input Stream! */
+  /* Configure I/O stream */
   if (has_input(stm)) {
     r = audiounit_configure_input(stm);
     if (r != CUBEB_OK) {
@@ -1690,7 +2610,6 @@ audiounit_setup_stream(cubeb_stream * stm)
     }
   }
 
-  /* Setup Output Stream! */
   if (has_output(stm)) {
     r = audiounit_configure_output(stm);
     if (r != CUBEB_OK) {
@@ -1762,13 +2681,13 @@ audiounit_setup_stream(cubeb_stream * stm)
 
   /* Create resampler. Output params are unchanged
    * because we do not need conversion on the output. */
-  stm->resampler = cubeb_resampler_create(stm,
-                                          has_input(stm) ? &input_unconverted_params : NULL,
-                                          has_output(stm) ? &stm->output_stream_params : NULL,
-                                          target_sample_rate,
-                                          stm->data_callback,
-                                          stm->user_ptr,
-                                          CUBEB_RESAMPLER_QUALITY_DESKTOP);
+  stm->resampler.reset(cubeb_resampler_create(stm,
+                                              has_input(stm) ? &input_unconverted_params : NULL,
+                                              has_output(stm) ? &stm->output_stream_params : NULL,
+                                              target_sample_rate,
+                                              stm->data_callback,
+                                              stm->user_ptr,
+                                              CUBEB_RESAMPLER_QUALITY_DESKTOP));
   if (!stm->resampler) {
     LOG("(%p) Could not create resampler.", stm);
     return CUBEB_ERROR;
@@ -1777,7 +2696,7 @@ audiounit_setup_stream(cubeb_stream * stm)
   if (stm->input_unit != NULL) {
     r = AudioUnitInitialize(stm->input_unit);
     if (r != noErr) {
-      PRINT_ERROR_CODE("AudioUnitInitialize/input", r);
+      LOG("AudioUnitInitialize/input rv=%d", r);
       return CUBEB_ERROR;
     }
   }
@@ -1785,9 +2704,17 @@ audiounit_setup_stream(cubeb_stream * stm)
   if (stm->output_unit != NULL) {
     r = AudioUnitInitialize(stm->output_unit);
     if (r != noErr) {
-      PRINT_ERROR_CODE("AudioUnitInitialize/output", r);
+      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) {
@@ -1799,13 +2726,24 @@ audiounit_setup_stream(cubeb_stream * stm)
 
   r = audiounit_install_device_changed_callback(stm);
   if (r != CUBEB_OK) {
-    LOG("(%p) Could not install the device change callback.", stm);
-    return r;
+    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,
@@ -1819,72 +2757,64 @@ audiounit_stream_init(cubeb * context,
                       cubeb_state_callback state_callback,
                       void * user_ptr)
 {
-  cubeb_stream * stm;
-  int r;
-
   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);
-  if (context->limit_streams && context->active_streams >= CUBEB_STREAM_MAX) {
-    LOG("Reached the stream limit of %d", CUBEB_STREAM_MAX);
-    return CUBEB_ERROR;
-  }
-
-  stm = (cubeb_stream *) calloc(1, sizeof(cubeb_stream));
-  assert(stm);
-  // Placement new to call the ctors of cubeb_stream members.
-  new (stm) cubeb_stream();
 
   /* These could be different in the future if we have both
    * full-duplex stream and different devices for input vs output. */
-  stm->context = context;
   stm->data_callback = data_callback;
   stm->state_callback = state_callback;
   stm->user_ptr = user_ptr;
   stm->latency_frames = latency_frames;
-  stm->device_changed_callback = NULL;
+
+  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;
-    stm->input_device = input_device;
-    stm->is_default_input = input_device == nullptr ||
-                            (audiounit_get_default_device_id(CUBEB_DEVICE_TYPE_INPUT) ==
-                                                  reinterpret_cast<intptr_t>(input_device));
+    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;
-    stm->output_device = output_device;
+    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;
+    }
   }
 
-  /* Init data members where necessary */
-  stm->hw_latency_frames = UINT64_MAX;
-
-  stm->switching_device = false;
-
-  auto_lock context_lock(context->mutex);
   {
     // 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`.
-    context->active_streams += 1;
     auto_lock lock(stm->mutex);
-    r = audiounit_setup_stream(stm);
+    r = audiounit_setup_stream(stm.get());
   }
 
   if (r != CUBEB_OK) {
-    LOG("(%p) Could not setup the audiounit stream.", stm);
-    audiounit_stream_destroy(stm);
+    LOG("(%p) Could not setup the audiounit stream.", stm.get());
     return r;
   }
 
-  r = audiounit_install_system_changed_callback(stm);
+  r = audiounit_install_system_changed_callback(stm.get());
   if (r != CUBEB_OK) {
-    LOG("(%p) Could not install the device change callback.", stm);
+    LOG("(%p) Could not install the device change callback.", stm.get());
     return r;
   }
 
-  *stream = stm;
-  LOG("Cubeb stream (%p) init successful.", stm);
+  *stream = stm.release();
+  LOG("(%p) Cubeb stream init successful.", *stream);
   return CUBEB_OK;
 }
 
@@ -1896,64 +2826,86 @@ audiounit_close_stream(cubeb_stream *stm)
   if (stm->input_unit) {
     AudioUnitUninitialize(stm->input_unit);
     AudioComponentInstanceDispose(stm->input_unit);
+    stm->input_unit = nullptr;
   }
 
-  audiounit_destroy_input_linear_buffer(stm);
+  stm->input_linear_buffer.reset();
 
   if (stm->output_unit) {
     AudioUnitUninitialize(stm->output_unit);
     AudioComponentInstanceDispose(stm->output_unit);
+    stm->output_unit = nullptr;
   }
 
-  cubeb_resampler_destroy(stm->resampler);
+  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(cubeb_stream * stm)
+audiounit_stream_destroy_internal(cubeb_stream *stm)
 {
-  stm->shutdown = true;
+  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 the device changed callback", stm);
+    LOG("(%p) Could not uninstall all device change listeners", stm);
   }
 
-  auto_lock context_lock(stm->context->mutex);
-  audiounit_stream_stop_internal(stm);
+  auto_lock lock(stm->mutex);
+  audiounit_close_stream(stm);
+  assert(audiounit_active_streams(stm->context) >= 1);
+  audiounit_decrement_active_streams(stm->context);
+}
 
+static void
+audiounit_stream_destroy(cubeb_stream * stm)
+{
+  if (!stm->shutdown.load()){
+    auto_lock context_lock(stm->context->mutex);
+    audiounit_stream_stop_internal(stm);
+    stm->shutdown = true;
+  }
+
+  stm->destroy_pending = true;
   // Execute close in serial queue to avoid collision
   // with reinit when un/plug devices
   dispatch_sync(stm->context->serial_queue, ^() {
-    auto_lock lock(stm->mutex);
-    audiounit_close_stream(stm);
+    auto_lock context_lock(stm->context->mutex);
+    audiounit_stream_destroy_internal(stm);
   });
 
-  assert(stm->context->active_streams >= 1);
-  stm->context->active_streams -= 1;
-
   LOG("Cubeb stream (%p) destroyed successful.", stm);
-
-  stm->~cubeb_stream();
-  free(stm);
+  delete stm;
 }
 
-void
+static int
 audiounit_stream_start_internal(cubeb_stream * stm)
 {
   OSStatus r;
   if (stm->input_unit != NULL) {
     r = AudioOutputUnitStart(stm->input_unit);
-    assert(r == 0);
+    if (r != noErr) {
+      LOG("AudioOutputUnitStart (input) rv=%d", r);
+      return CUBEB_ERROR;
+    }
   }
   if (stm->output_unit != NULL) {
     r = AudioOutputUnitStart(stm->output_unit);
-    assert(r == 0);
+    if (r != noErr) {
+      LOG("AudioOutputUnitStart (output) rv=%d", r);
+      return CUBEB_ERROR;
+    }
   }
+  return CUBEB_OK;
 }
 
 static int
@@ -1963,7 +2915,10 @@ audiounit_stream_start(cubeb_stream * stm)
   stm->shutdown = false;
   stm->draining = false;
 
-  audiounit_stream_start_internal(stm);
+  int r = audiounit_stream_start_internal(stm);
+  if (r != CUBEB_OK) {
+    return r;
+  }
 
   stm->state_callback(stm, stm->user_ptr, CUBEB_STATE_STARTED);
 
@@ -2002,9 +2957,12 @@ audiounit_stream_stop(cubeb_stream * stm)
 static int
 audiounit_stream_get_position(cubeb_stream * stm, uint64_t * position)
 {
-  auto_lock lock(stm->mutex);
-
-  *position = stm->frames_played;
+  assert(stm);
+  if (stm->current_latency_frames > stm->frames_played) {
+    *position = 0;
+  } else {
+    *position = stm->frames_played - stm->current_latency_frames;
+  }
   return CUBEB_OK;
 }
 
@@ -2015,74 +2973,7 @@ audiounit_stream_get_latency(cubeb_stream * stm, uint32_t * latency)
   //TODO
   return CUBEB_ERROR_NOT_SUPPORTED;
 #else
-  auto_lock lock(stm->mutex);
-  if (stm->hw_latency_frames == UINT64_MAX) {
-    UInt32 size;
-    uint32_t device_latency_frames, device_safety_offset;
-    double unit_latency_sec;
-    AudioDeviceID output_device_id;
-    OSStatus r;
-    AudioObjectPropertyAddress latency_address = {
-      kAudioDevicePropertyLatency,
-      kAudioDevicePropertyScopeOutput,
-      kAudioObjectPropertyElementMaster
-    };
-    AudioObjectPropertyAddress safety_offset_address = {
-      kAudioDevicePropertySafetyOffset,
-      kAudioDevicePropertyScopeOutput,
-      kAudioObjectPropertyElementMaster
-    };
-
-    r = audiounit_get_output_device_id(&output_device_id);
-    if (r != noErr) {
-      return CUBEB_ERROR;
-    }
-
-    size = sizeof(unit_latency_sec);
-    r = AudioUnitGetProperty(stm->output_unit,
-                             kAudioUnitProperty_Latency,
-                             kAudioUnitScope_Global,
-                             0,
-                             &unit_latency_sec,
-                             &size);
-    if (r != noErr) {
-      PRINT_ERROR_CODE("AudioUnitGetProperty/kAudioUnitProperty_Latency", r);
-      return CUBEB_ERROR;
-    }
-
-    size = sizeof(device_latency_frames);
-    r = AudioObjectGetPropertyData(output_device_id,
-                                   &latency_address,
-                                   0,
-                                   NULL,
-                                   &size,
-                                   &device_latency_frames);
-    if (r != noErr) {
-      PRINT_ERROR_CODE("AudioUnitGetPropertyData/latency_frames", r);
-      return CUBEB_ERROR;
-    }
-
-    size = sizeof(device_safety_offset);
-    r = AudioObjectGetPropertyData(output_device_id,
-                                   &safety_offset_address,
-                                   0,
-                                   NULL,
-                                   &size,
-                                   &device_safety_offset);
-    if (r != noErr) {
-      PRINT_ERROR_CODE("AudioUnitGetPropertyData/safety_offset", r);
-      return CUBEB_ERROR;
-    }
-
-    /* This part is fixed and depend on the stream parameter and the hardware. */
-    stm->hw_latency_frames =
-      static_cast<uint32_t>(unit_latency_sec * stm->output_desc.mSampleRate)
-      + device_latency_frames
-      + device_safety_offset;
-  }
-
-  *latency = stm->hw_latency_frames + stm->current_latency_frames;
-
+  *latency = stm->total_output_latency_frames;
   return CUBEB_OK;
 #endif
 }
@@ -2102,119 +2993,110 @@ audiounit_stream_get_volume(cubeb_stream * stm, float * volume)
   return CUBEB_OK;
 }
 
-int audiounit_stream_set_volume(cubeb_stream * stm, float volume)
+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) {
-    PRINT_ERROR_CODE("AudioUnitSetParameter/kHALOutputParam_Volume", r);
+    LOG("AudioUnitSetParameter/kHALOutputParam_Volume rv=%d", r);
     return CUBEB_ERROR;
   }
   return CUBEB_OK;
 }
 
-int audiounit_stream_set_panning(cubeb_stream * stm, float panning)
+unique_ptr<char[]> convert_uint32_into_string(UInt32 data)
 {
-  if (stm->output_desc.mChannelsPerFrame > 2) {
-    return CUBEB_ERROR_INVALID_PARAMETER;
+  // 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;
   }
 
-  stm->panning.store(panning, std::memory_order_relaxed);
-  return CUBEB_OK;
+  // 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_stream_get_current_device(cubeb_stream * stm,
-                                        cubeb_device ** const  device)
+int audiounit_get_default_device_datasource(cubeb_device_type type,
+                                            UInt32 * data)
 {
-#if TARGET_OS_IPHONE
-  //TODO
-  return CUBEB_ERROR_NOT_SUPPORTED;
-#else
-  OSStatus r;
-  UInt32 size;
-  UInt32 data;
-  char strdata[4];
-  AudioDeviceID output_device_id;
-  AudioDeviceID input_device_id;
-
-  AudioObjectPropertyAddress datasource_address = {
-    kAudioDevicePropertyDataSource,
-    kAudioDevicePropertyScopeOutput,
-    kAudioObjectPropertyElementMaster
-  };
-
-  AudioObjectPropertyAddress datasource_address_input = {
-    kAudioDevicePropertyDataSource,
-    kAudioDevicePropertyScopeInput,
-    kAudioObjectPropertyElementMaster
-  };
-
-  *device = NULL;
-
-  if (audiounit_get_output_device_id(&output_device_id) != CUBEB_OK) {
+  AudioDeviceID id = audiounit_get_default_device_id(type);
+  if (id == kAudioObjectUnknown) {
     return CUBEB_ERROR;
   }
 
-  *device = new cubeb_device;
-  if (!*device) {
-    return CUBEB_ERROR;
-  }
-  PodZero(*device, 1);
-
-  size = sizeof(UInt32);
-  /* This fails with some USB headset, so simply return an empty string. */
-  r = AudioObjectGetPropertyData(output_device_id,
-                                 &datasource_address,
-                                 0, NULL, &size, &data);
+  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) {
-    size = 0;
-    data = 0;
-  }
-
-  (*device)->output_name = new char[size + 1];
-  if (!(*device)->output_name) {
-    return CUBEB_ERROR;
+    *data = 0;
   }
 
-  // Turn the four chars packed into a uint32 into a string
-  strdata[0] = (char)(data >> 24);
-  strdata[1] = (char)(data >> 16);
-  strdata[2] = (char)(data >> 8);
-  strdata[3] = (char)(data);
+  return CUBEB_OK;
+}
 
-  memcpy((*device)->output_name, strdata, size);
-  (*device)->output_name[size] = '\0';
+int audiounit_get_default_device_name(cubeb_stream * stm,
+                                      cubeb_device * const device,
+                                      cubeb_device_type type)
+{
+  assert(stm);
+  assert(device);
 
-  if (audiounit_get_input_device_id(&input_device_id) != CUBEB_OK) {
-    return CUBEB_ERROR;
+  UInt32 data;
+  int r = audiounit_get_default_device_datasource(type, &data);
+  if (r != CUBEB_OK) {
+    return r;
   }
-
-  size = sizeof(UInt32);
-  r = AudioObjectGetPropertyData(input_device_id, &datasource_address_input, 0, NULL, &size, &data);
-  if (r != noErr) {
-    LOG("(%p) Error when getting device !", stm);
-    size = 0;
-    data = 0;
+  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;
+}
 
-  (*device)->input_name = new char[size + 1];
-  if (!(*device)->input_name) {
+
+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);
 
-  // Turn the four chars packed into a uint32 into a string
-  strdata[0] = (char)(data >> 24);
-  strdata[1] = (char)(data >> 16);
-  strdata[2] = (char)(data >> 8);
-  strdata[3] = (char)(data);
+  int r = audiounit_get_default_device_name(stm, *device,
+                                            CUBEB_DEVICE_TYPE_OUTPUT);
+  if (r != CUBEB_OK) {
+    return r;
+  }
 
-  memcpy((*device)->input_name, strdata, size);
-  (*device)->input_name[size] = '\0';
+  r = audiounit_get_default_device_name(stm, *device,
+                                        CUBEB_DEVICE_TYPE_INPUT);
+  if (r != CUBEB_OK) {
+    return r;
+  }
 
   return CUBEB_OK;
 #endif
@@ -2232,52 +3114,14 @@ int audiounit_stream_device_destroy(cubeb_stream * /* stream */,
 int audiounit_stream_register_device_changed_callback(cubeb_stream * stream,
                                                       cubeb_device_changed_callback device_changed_callback)
 {
+  auto_lock dev_cb_lock(stream->device_changed_callback_lock);
   /* Note: second register without unregister first causes 'nope' error.
    * Current implementation requires unregister before register a new cb. */
-  assert(!stream->device_changed_callback);
-
-  auto_lock lock(stream->mutex);
-
+  assert(!device_changed_callback || !stream->device_changed_callback);
   stream->device_changed_callback = device_changed_callback;
-
   return CUBEB_OK;
 }
 
-static OSStatus
-audiounit_get_devices(AudioObjectID ** devices, uint32_t * count)
-{
-  OSStatus ret;
-  UInt32 size = 0;
-  AudioObjectPropertyAddress adr = { kAudioHardwarePropertyDevices,
-                                     kAudioObjectPropertyScopeGlobal,
-                                     kAudioObjectPropertyElementMaster };
-
-  ret = AudioObjectGetPropertyDataSize(kAudioObjectSystemObject, &adr, 0, NULL, &size);
-  if (ret != noErr) {
-    return ret;
-  }
-
-  *count = static_cast<uint32_t>(size / sizeof(AudioObjectID));
-  if (size >= sizeof(AudioObjectID)) {
-    if (*devices != NULL) {
-      delete [] (*devices);
-    }
-    *devices = new AudioObjectID[*count];
-    PodZero(*devices, *count);
-
-    ret = AudioObjectGetPropertyData(kAudioObjectSystemObject, &adr, 0, NULL, &size, (void *)*devices);
-    if (ret != noErr) {
-      delete [] (*devices);
-      *devices = NULL;
-    }
-  } else {
-    *devices = NULL;
-    ret = -1;
-  }
-
-  return ret;
-}
-
 static char *
 audiounit_strref_to_cstr_utf8(CFStringRef strref)
 {
@@ -2288,11 +3132,12 @@ audiounit_strref_to_cstr_utf8(CFStringRef strref)
   }
 
   len = CFStringGetLength(strref);
-  size = CFStringGetMaximumSizeForEncoding(len, kCFStringEncodingUTF8);
-  ret = static_cast<char *>(malloc(size));
+  // 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)) {
-    free(ret);
+    delete [] ret;
     ret = NULL;
   }
 
@@ -2339,19 +3184,18 @@ audiounit_get_available_samplerate(AudioObjectID devid, AudioObjectPropertyScope
   AudioValueRange range;
   if (AudioObjectHasProperty(devid, &adr) &&
       AudioObjectGetPropertyDataSize(devid, &adr, 0, NULL, &size) == noErr) {
-    uint32_t i, count = size / sizeof(AudioValueRange);
-    AudioValueRange * ranges = new AudioValueRange[count];
+    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) == noErr) {
-      for (i = 0; i < count; i++) {
+    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;
       }
     }
-    delete [] ranges;
     *max = static_cast<uint32_t>(range.mMaximum);
     *min = static_cast<uint32_t>(range.mMinimum);
   } else {
@@ -2364,7 +3208,7 @@ static UInt32
 audiounit_get_device_presentation_latency(AudioObjectID devid, AudioObjectPropertyScope scope)
 {
   AudioObjectPropertyAddress adr = { 0, scope, kAudioObjectPropertyElementMaster };
-  UInt32 size, dev, stream = 0, offset;
+  UInt32 size, dev, stream = 0;
   AudioStreamID sid[1];
 
   adr.mSelector = kAudioDevicePropertyLatency;
@@ -2381,216 +3225,249 @@ audiounit_get_device_presentation_latency(AudioObjectID devid, AudioObjectProper
     AudioObjectGetPropertyData(sid[0], &adr, 0, NULL, &size, &stream);
   }
 
-  adr.mSelector = kAudioDevicePropertySafetyOffset;
-  size = sizeof(UInt32);
-  if (AudioObjectGetPropertyData(devid, &adr, 0, NULL, &size, &offset) != noErr) {
-    offset = 0;
-  }
-
-  return dev + stream + offset;
+  return dev + stream;
 }
 
-static cubeb_device_info *
-audiounit_create_device_from_hwdev(AudioObjectID devid, cubeb_device_type type)
+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, ch, latency;
-  cubeb_device_info * ret;
-  CFStringRef str = NULL;
-  AudioValueRange range;
+  UInt32 size;
 
   if (type == CUBEB_DEVICE_TYPE_OUTPUT) {
     adr.mScope = kAudioDevicePropertyScopeOutput;
   } else if (type == CUBEB_DEVICE_TYPE_INPUT) {
     adr.mScope = kAudioDevicePropertyScopeInput;
   } else {
-    return NULL;
+    return CUBEB_ERROR;
   }
 
-  ch = audiounit_get_channel_count(devid, adr.mScope);
+  UInt32 ch = audiounit_get_channel_count(devid, adr.mScope);
   if (ch == 0) {
-    return NULL;
+    return CUBEB_ERROR;
   }
 
-  ret = new cubeb_device_info;
-  PodZero(ret, 1);
+  PodZero(dev_info, 1);
 
+  CFStringRef device_id_str = nullptr;
   size = sizeof(CFStringRef);
   adr.mSelector = kAudioDevicePropertyDeviceUID;
-  if (AudioObjectGetPropertyData(devid, &adr, 0, NULL, &size, &str) == noErr && str != NULL) {
-    ret->device_id = audiounit_strref_to_cstr_utf8(str);
-    ret->devid = (cubeb_devid)(size_t)devid;
-    ret->group_id = strdup(ret->device_id);
-    CFRelease(str);
+  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);
   }
 
-  size = sizeof(CFStringRef);
-  adr.mSelector = kAudioObjectPropertyName;
-  if (AudioObjectGetPropertyData(devid, &adr, 0, NULL, &size, &str) == noErr && str != NULL) {
-    UInt32 ds;
-    size = sizeof(UInt32);
-    adr.mSelector = kAudioDevicePropertyDataSource;
-    if (AudioObjectGetPropertyData(devid, &adr, 0, NULL, &size, &ds) == noErr) {
-      CFStringRef dsname;
-      AudioValueTranslation trl = { &ds, sizeof(ds), &dsname, sizeof(dsname) };
-      adr.mSelector = kAudioDevicePropertyDataSourceNameForIDCFString;
-      size = sizeof(AudioValueTranslation);
-      // If there is a datasource for this device, use it instead of the device
-      // name.
-      if (AudioObjectGetPropertyData(devid, &adr, 0, NULL, &size, &trl) == noErr) {
-        CFRelease(str);
-        str = dsname;
-      }
-    }
+  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);
+  }
 
-    ret->friendly_name = audiounit_strref_to_cstr_utf8(str);
-    CFRelease(str);
+  // 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;
-  if (AudioObjectGetPropertyData(devid, &adr, 0, NULL, &size, &str) == noErr && str != NULL) {
-    ret->vendor_name = audiounit_strref_to_cstr_utf8(str);
-    CFRelease(str);
+  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);
   }
 
-  ret->type = type;
-  ret->state = CUBEB_DEVICE_STATE_ENABLED;
-  ret->preferred = (devid == audiounit_get_default_device_id(type)) ?
+  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;
 
-  ret->max_channels = ch;
-  ret->format = (cubeb_device_fmt)CUBEB_DEVICE_FMT_ALL; /* CoreAudio supports All! */
+  dev_info->max_channels = ch;
+  dev_info->format = (cubeb_device_fmt)CUBEB_DEVICE_FMT_ALL; /* CoreAudio supports All! */
   /* kAudioFormatFlagsAudioUnitCanonical is deprecated, prefer floating point */
-  ret->default_format = CUBEB_DEVICE_FMT_F32NE;
+  dev_info->default_format = CUBEB_DEVICE_FMT_F32NE;
   audiounit_get_available_samplerate(devid, adr.mScope,
-      &ret->min_rate, &ret->max_rate, &ret->default_rate);
+                                     &dev_info->min_rate, &dev_info->max_rate, &dev_info->default_rate);
 
-  latency = audiounit_get_device_presentation_latency(devid, adr.mScope);
+  UInt32 latency = audiounit_get_device_presentation_latency(devid, adr.mScope);
 
+  AudioValueRange range;
   adr.mSelector = kAudioDevicePropertyBufferFrameSizeRange;
   size = sizeof(AudioValueRange);
-  if (AudioObjectGetPropertyData(devid, &adr, 0, NULL, &size, &range) == noErr) {
-    ret->latency_lo = latency + range.mMinimum;
-    ret->latency_hi = latency + range.mMaximum;
+  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 {
-    ret->latency_lo = 10 * ret->default_rate / 1000;  /* Default to  10ms */
-    ret->latency_hi = 100 * ret->default_rate / 1000; /* Default to 100ms */
+    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 ret;
+  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)
+                            cubeb_device_collection * collection)
 {
-  AudioObjectID * hwdevs = NULL;
-  uint32_t i, hwdevcount = 0;
-  OSStatus err;
+  vector<AudioObjectID> input_devs;
+  vector<AudioObjectID> output_devs;
 
-  if ((err = audiounit_get_devices(&hwdevs, &hwdevcount)) != noErr) {
-    return CUBEB_ERROR;
+  // 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);
   }
 
-  *collection = static_cast<cubeb_device_collection *>(malloc(sizeof(cubeb_device_collection) +
-      sizeof(cubeb_device_info*) * (hwdevcount > 0 ? hwdevcount - 1 : 0)));
-  (*collection)->count = 0;
+  if (type & CUBEB_DEVICE_TYPE_INPUT) {
+    input_devs = audiounit_get_devices_of_type(CUBEB_DEVICE_TYPE_INPUT);
+  }
 
-  if (hwdevcount > 0) {
-    cubeb_device_info * cur;
+  auto devices = new cubeb_device_info[output_devs.size() + input_devs.size()];
+  collection->count = 0;
 
-    if (type & CUBEB_DEVICE_TYPE_OUTPUT) {
-      for (i = 0; i < hwdevcount; i++) {
-        if ((cur = audiounit_create_device_from_hwdev(hwdevs[i], CUBEB_DEVICE_TYPE_OUTPUT)) != NULL)
-          (*collection)->device[(*collection)->count++] = cur;
+  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 (i = 0; i < hwdevcount; i++) {
-        if ((cur = audiounit_create_device_from_hwdev(hwdevs[i], CUBEB_DEVICE_TYPE_INPUT)) != NULL)
-          (*collection)->device[(*collection)->count++] = cur;
+  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;
     }
   }
 
-  delete [] hwdevs;
+  if (collection->count > 0) {
+    collection->device = devices;
+  } else {
+    delete [] devices;
+    collection->device = NULL;
+  }
 
   return CUBEB_OK;
 }
 
-/* qsort compare method. */
-int compare_devid(const void * a, const void * b)
+static void
+audiounit_device_destroy(cubeb_device_info * device)
 {
-  return (*(AudioObjectID*)a - *(AudioObjectID*)b);
+  delete [] device->device_id;
+  delete [] device->friendly_name;
+  delete [] device->vendor_name;
 }
 
-static uint32_t
-audiounit_get_devices_of_type(cubeb_device_type devtype, AudioObjectID ** devid_array)
+static int
+audiounit_device_collection_destroy(cubeb * /* context */,
+                                    cubeb_device_collection * collection)
 {
-  assert(devid_array == NULL || *devid_array == NULL);
+  for (size_t i = 0; i < collection->count; i++) {
+    audiounit_device_destroy(&collection->device[i]);
+  }
+  delete [] collection->device;
 
-  AudioObjectPropertyAddress adr = { kAudioHardwarePropertyDevices,
-                                     kAudioObjectPropertyScopeGlobal,
-                                     kAudioObjectPropertyElementMaster };
+  return CUBEB_OK;
+}
+
+static vector<AudioObjectID>
+audiounit_get_devices_of_type(cubeb_device_type devtype)
+{
   UInt32 size = 0;
-  OSStatus ret = AudioObjectGetPropertyDataSize(kAudioObjectSystemObject, &adr, 0, NULL, &size);
+  OSStatus ret = AudioObjectGetPropertyDataSize(kAudioObjectSystemObject,
+                                                &DEVICES_PROPERTY_ADDRESS, 0,
+                                                NULL, &size);
   if (ret != noErr) {
-    return 0;
+    return vector<AudioObjectID>();
   }
-  /* Total number of input and output devices. */
-  uint32_t count = (uint32_t)(size / sizeof(AudioObjectID));
-
-  AudioObjectID devices[count];
-  ret = AudioObjectGetPropertyData(kAudioObjectSystemObject, &adr, 0, NULL, &size, &devices);
+  vector<AudioObjectID> devices(size / sizeof(AudioObjectID));
+  ret = AudioObjectGetPropertyData(kAudioObjectSystemObject,
+                                   &DEVICES_PROPERTY_ADDRESS, 0, NULL, &size,
+                                   devices.data());
   if (ret != noErr) {
-    return 0;
+    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. */
-  qsort(devices, count, sizeof(AudioObjectID), compare_devid);
+  sort(devices.begin(), devices.end(), [](AudioObjectID a, AudioObjectID b) {
+      return a < b;
+    });
 
   if (devtype == (CUBEB_DEVICE_TYPE_INPUT | CUBEB_DEVICE_TYPE_OUTPUT)) {
-    if (devid_array) {
-      *devid_array = new AudioObjectID[count];
-      assert(*devid_array);
-      memcpy(*devid_array, &devices, count * sizeof(AudioObjectID));
-    }
-    return count;
+    return devices;
   }
 
   AudioObjectPropertyScope scope = (devtype == CUBEB_DEVICE_TYPE_INPUT) ?
                                          kAudioDevicePropertyScopeInput :
                                          kAudioDevicePropertyScopeOutput;
 
-  uint32_t dev_count = 0;
-  AudioObjectID devices_in_scope[count];
-  for(uint32_t i = 0; i < count; ++i) {
+  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[dev_count] = devices[i];
-      ++dev_count;
+      devices_in_scope.push_back(devices[i]);
     }
   }
 
-  if (devid_array && dev_count > 0) {
-    *devid_array = new AudioObjectID[dev_count];
-    assert(*devid_array);
-    memcpy(*devid_array, &devices_in_scope, dev_count * sizeof(AudioObjectID));
-  }
-  return dev_count;
-}
-
-static uint32_t
-audiounit_equal_arrays(AudioObjectID * left, AudioObjectID * right, uint32_t size)
-{
-  /* Expected sorted arrays. */
-  for (uint32_t i = 0; i < size; ++i) {
-    if (left[i] != right[i]) {
-      return 0;
-    }
-  }
-  return 1;
+  return devices_in_scope;
 }
 
 static OSStatus
@@ -2600,33 +3477,32 @@ audiounit_collection_changed_callback(AudioObjectID /* inObjectID */,
                                       void * inClientData)
 {
   cubeb * context = static_cast<cubeb *>(inClientData);
-  auto_lock lock(context->mutex);
-
-  if (context->collection_changed_callback == NULL) {
-    /* Listener removed while waiting in mutex, abort. */
-    return noErr;
-  }
 
-  /* Differentiate input from output changes. */
-  if (context->collection_changed_devtype == CUBEB_DEVICE_TYPE_INPUT ||
-      context->collection_changed_devtype == CUBEB_DEVICE_TYPE_OUTPUT) {
-    AudioObjectID * devices = NULL;
-    uint32_t new_number_of_devices = audiounit_get_devices_of_type(context->collection_changed_devtype, &devices);
-    /* When count is the same examine the devid for the case of coalescing. */
-    if (context->devtype_device_count == new_number_of_devices &&
-        audiounit_equal_arrays(devices, context->devtype_device_array, new_number_of_devices)) {
-      /* Device changed for the other scope, ignore. */
-      delete [] devices;
-      return noErr;
+  // 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;
     }
-    /* Device on desired scope changed, reset counter and array. */
-    context->devtype_device_count = new_number_of_devices;
-    /* Free the old array before replace. */
-    delete [] context->devtype_device_array;
-    context->devtype_device_array = devices;
-  }
-
-  context->collection_changed_callback(context, context->collection_changed_user_ptr);
+    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;
 }
 
@@ -2636,62 +3512,65 @@ audiounit_add_device_listener(cubeb * context,
                               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(context->collection_changed_callback == NULL);
-
-  AudioObjectPropertyAddress devAddr;
-  devAddr.mSelector = kAudioHardwarePropertyDevices;
-  devAddr.mScope = kAudioObjectPropertyScopeGlobal;
-  devAddr.mElement = kAudioObjectPropertyElementMaster;
-
-  OSStatus ret = AudioObjectAddPropertyListener(kAudioObjectSystemObject,
-                                                &devAddr,
-                                                audiounit_collection_changed_callback,
-                                                context);
-  if (ret == noErr) {
-    /* Expected zero after unregister. */
-    assert(context->devtype_device_count == 0);
-    assert(context->devtype_device_array == NULL);
-    /* Listener works for input and output.
-     * When requested one of them we need to differentiate. */
-    if (devtype == CUBEB_DEVICE_TYPE_INPUT ||
-        devtype == CUBEB_DEVICE_TYPE_OUTPUT) {
-      /* Used to differentiate input from output device changes. */
-      context->devtype_device_count = audiounit_get_devices_of_type(devtype, &context->devtype_device_array);
-    }
-    context->collection_changed_devtype = devtype;
-    context->collection_changed_callback = collection_changed_callback;
-    context->collection_changed_user_ptr = user_ptr;
+  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;
+    }
   }
-  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)
+audiounit_remove_device_listener(cubeb * context, cubeb_device_type devtype)
 {
-  AudioObjectPropertyAddress devAddr;
-  devAddr.mSelector = kAudioHardwarePropertyDevices;
-  devAddr.mScope = kAudioObjectPropertyScopeGlobal;
-  devAddr.mElement = kAudioObjectPropertyElementMaster;
+  context->mutex.assert_current_thread_owns();
 
-  /* Note: unregister a non registered cb is not a problem, not checking. */
-  OSStatus ret = AudioObjectRemovePropertyListener(kAudioObjectSystemObject,
-                                                   &devAddr,
-                                                   audiounit_collection_changed_callback,
-                                                   context);
-  if (ret == noErr) {
-    /* Reset all values. */
-    context->collection_changed_devtype = CUBEB_DEVICE_TYPE_UNKNOWN;
-    context->collection_changed_callback = NULL;
-    context->collection_changed_user_ptr = NULL;
-    context->devtype_device_count = 0;
-    if (context->devtype_device_array) {
-      delete [] context->devtype_device_array;
-      context->devtype_device_array = NULL;
-    }
+  if (devtype & CUBEB_DEVICE_TYPE_INPUT) {
+    context->input_collection_changed_callback = nullptr;
+    context->input_collection_changed_user_ptr = nullptr;
+    context->input_device_array.clear();
   }
-  return ret;
+  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,
@@ -2699,14 +3578,18 @@ int audiounit_register_device_collection_changed(cubeb * context,
                                                  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,
+    ret = audiounit_add_device_listener(context,
+                                        devtype,
                                         collection_changed_callback,
                                         user_ptr);
   } else {
-    ret = audiounit_remove_device_listener(context);
+    ret = audiounit_remove_device_listener(context, devtype);
   }
   return (ret == noErr) ? CUBEB_OK : CUBEB_ERROR;
 }
@@ -2718,15 +3601,16 @@ cubeb_ops const audiounit_ops = {
   /*.get_min_latency =*/ audiounit_get_min_latency,
   /*.get_preferred_sample_rate =*/ audiounit_get_preferred_sample_rate,
   /*.enumerate_devices =*/ audiounit_enumerate_devices,
+  /*.device_collection_destroy =*/ audiounit_device_collection_destroy,
   /*.destroy =*/ audiounit_destroy,
   /*.stream_init =*/ audiounit_stream_init,
   /*.stream_destroy =*/ audiounit_stream_destroy,
   /*.stream_start =*/ audiounit_stream_start,
   /*.stream_stop =*/ audiounit_stream_stop,
+  /*.stream_reset_default_device =*/ nullptr,
   /*.stream_get_position =*/ audiounit_stream_get_position,
   /*.stream_get_latency =*/ audiounit_stream_get_latency,
   /*.stream_set_volume =*/ audiounit_stream_set_volume,
-  /*.stream_set_panning =*/ audiounit_stream_set_panning,
   /*.stream_get_current_device =*/ audiounit_stream_get_current_device,
   /*.stream_device_destroy =*/ audiounit_stream_device_destroy,
   /*.stream_register_device_changed_callback =*/ audiounit_stream_register_device_changed_callback,