Add Mac OS X synchronized audio I/O back-end

media/audio/mac/audio_synchronized_mac.cc

Index: media/audio/mac/audio_synchronized_mac.cc
===================================================================
--- media/audio/mac/audio_synchronized_mac.cc	(revision 0)
+++ media/audio/mac/audio_synchronized_mac.cc	(revision 0)
@@ -0,0 +1,945 @@
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "media/audio/mac/audio_synchronized_mac.h"
+
+#include <CoreServices/CoreServices.h>
+#include <algorithm>
+
+#include "base/basictypes.h"
+#include "base/debug/trace_event.h"
+#include "base/logging.h"
+#include "base/mac/mac_logging.h"
+#include "media/audio/audio_util.h"
+#include "media/audio/mac/audio_manager_mac.h"
+
+namespace media {
+
+static const int kHardwareBufferSize = 128;
+static const int kFifoSize = 16384;
+
+// TODO(crogers): handle the non-stereo case.
+static const int kChannels = 2;
+
+// This value was determined empirically for minimum latency while still
+// guarding against FIFO under-runs.
+static const int kBaseTargetFifoFrames = 256 + 64;
+
+// If the input and output sample-rate don't match, then we need to maintain
+// an additional safety margin due to the callback timing jitter and the
+// varispeed buffering.  This value was empirically tuned.
+static const int kAdditionalTargetFifoFrames = 128;
+
+static void ZeroBufferList(AudioBufferList* buffer_list) {
+  for (size_t i = 0; i < buffer_list->mNumberBuffers; ++i)
+    memset(buffer_list->mBuffers[i].mData,
+           0,
+           buffer_list->mBuffers[i].mDataByteSize);
+}
+
+static void WrapBufferList(AudioBufferList* buffer_list,
+                           AudioBus* bus,
+                           int frames) {
+  DCHECK(buffer_list);
+  DCHECK(bus);
+  int channels = bus->channels();
+  int buffer_list_channels = buffer_list->mNumberBuffers;
+
+  // Copy pointers from AudioBufferList.
+  // It's ok to pass in a |buffer_list| with fewer channels, in which

[scherkus (not reviewing), 2012/09/17 23:07:17]

update comment?

I'm not seeing us pass stuff in

[Chris Rogers, 2012/09/18 00:22:36]

I've moved part of this comment down to line 57 where it really applies.

+  // case we just duplicate the last channel.
+  int source_idx = 0;
+  for (int i = 0; i < channels; ++i) {
+    bus->SetChannelData(
+        i, static_cast<float*>(buffer_list->mBuffers[source_idx].mData));
+
+    if (source_idx < buffer_list_channels - 1)
+      ++source_idx;
+  }
+
+  // Finally set the actual length.
+  bus->set_frames(frames);
+}
+
+AudioSynchronizedStream::AudioSynchronizedStream(
+    AudioManagerMac* manager,
+    const AudioParameters& params,
+    AudioDeviceID input_id,
+    AudioDeviceID output_id)
+    : manager_(manager),
+      params_(params),
+      input_sample_rate_(0),
+      output_sample_rate_(0),
+      input_id_(input_id),
+      output_id_(output_id),
+      input_buffer_list_(NULL),
+      fifo_(kChannels, kFifoSize),
+      target_fifo_frames_(kBaseTargetFifoFrames),
+      average_delta_(0.0),
+      fifo_rate_compensation_(1.0),
+      input_unit_(0),
+      varispeed_unit_(0),
+      output_unit_(0),
+      first_input_time_(-1),
+      is_running_(false),
+      hardware_buffer_size_(kHardwareBufferSize),
+      channels_(kChannels) {
+}
+
+AudioSynchronizedStream::~AudioSynchronizedStream() {
+  DCHECK(!input_unit_);
+  DCHECK(!output_unit_);
+  DCHECK(!varispeed_unit_);
+}
+
+bool AudioSynchronizedStream::Open() {
+  if (params_.channels() != kChannels) {
+    LOG(ERROR) << "Only stereo output is currently supported.";
+    return false;
+  }
+
+  // Create the input, output, and varispeed AudioUnits.
+  OSStatus result = CreateAudioUnits();
+  if (result != noErr) {
+    LOG(ERROR) << "Cannot create AudioUnits.";
+    return false;
+  }
+
+  result = SetupInput(input_id_);
+  if (result != noErr) {
+    LOG(ERROR) << "Error configuring input AudioUnit.";
+    return false;
+  }
+
+  result = SetupOutput(output_id_);
+  if (result != noErr) {
+    LOG(ERROR) << "Error configuring output AudioUnit.";
+    return false;
+  }
+
+  result = SetupCallbacks();
+  if (result != noErr) {
+    LOG(ERROR) << "Error setting up callbacks on AudioUnits.";
+    return false;
+  }
+
+  result = SetupStreamFormats();
+  if (result != noErr) {
+    LOG(ERROR) << "Error configuring stream formats on AudioUnits.";
+    return false;
+  }
+
+  AllocateInputData();
+
+  // Final initialization of the AudioUnits.
+  result = AudioUnitInitialize(input_unit_);
+  if (result != noErr) {
+    LOG(ERROR) << "Error initializing input AudioUnit.";
+    return false;
+  }
+
+  result = AudioUnitInitialize(output_unit_);
+  if (result != noErr) {
+    LOG(ERROR) << "Error initializing output AudioUnit.";
+    return false;
+  }
+
+  result = AudioUnitInitialize(varispeed_unit_);
+  if (result != noErr) {
+    LOG(ERROR) << "Error initializing varispeed AudioUnit.";
+    return false;
+  }
+
+  if (input_sample_rate_ != output_sample_rate_) {
+    // Add extra safety margin.
+    target_fifo_frames_ += kAdditionalTargetFifoFrames;
+  }
+
+  // Buffer initial silence corresponding to target I/O buffering.
+  fifo_.Clear();
+  scoped_ptr<AudioBus> silence =
+      AudioBus::Create(channels_, target_fifo_frames_);
+  silence->Zero();
+  fifo_.Push(silence.get());
+
+  return true;
+}
+
+void AudioSynchronizedStream::Close() {
+  DCHECK(!is_running_);
+
+  if (input_buffer_list_) {
+    free(input_buffer_list_);
+    input_buffer_list_ = 0;
+    input_bus_.reset(NULL);
+    wrapper_bus_.reset(NULL);
+  }
+
+  if (input_unit_) {
+    AudioUnitUninitialize(input_unit_);
+    CloseComponent(input_unit_);
+  }
+
+  if (output_unit_) {
+    AudioUnitUninitialize(output_unit_);
+    CloseComponent(output_unit_);
+  }
+
+  if (varispeed_unit_) {
+    AudioUnitUninitialize(varispeed_unit_);
+    CloseComponent(varispeed_unit_);
+  }
+
+  input_unit_ = NULL;
+  output_unit_ = NULL;
+  varispeed_unit_ = NULL;
+
+  // Inform the audio manager that we have been closed. This can cause our
+  // destruction.
+  manager_->ReleaseOutputStream(this);
+}
+
+void AudioSynchronizedStream::Start(AudioSourceCallback* callback) {
+  DCHECK(callback);
+  DCHECK(input_unit_);
+  DCHECK(output_unit_);
+  DCHECK(varispeed_unit_);
+
+  if (is_running_ || !input_unit_ || !output_unit_ || !varispeed_unit_)
+    return;
+
+  source_ = callback;
+
+  // Reset state variables each time we Start().
+  fifo_rate_compensation_ = 1.0;
+  average_delta_ = 0.0;
+
+  OSStatus result = noErr;
+
+  if (!is_running_) {
+    first_input_time_ = -1;
+
+    result = AudioOutputUnitStart(input_unit_);
+    OSSTATUS_DCHECK(result == noErr, result);
+
+    if (result == noErr) {
+      result = AudioOutputUnitStart(output_unit_);
+      OSSTATUS_DCHECK(result == noErr, result);
+    }
+  }
+
+  is_running_ = true;
+}
+
+void AudioSynchronizedStream::Stop() {
+  OSStatus result = noErr;
+  if (is_running_) {
+    result = AudioOutputUnitStop(input_unit_);
+    OSSTATUS_DCHECK(result == noErr, result);
+
+    if (result == noErr) {
+      result = AudioOutputUnitStop(output_unit_);
+      OSSTATUS_DCHECK(result == noErr, result);
+    }
+  }
+
+  if (result == noErr)
+    is_running_ = false;
+}
+
+bool AudioSynchronizedStream::IsRunning() {
+  return is_running_;
+}
+
+// TODO(crogers): implement - or remove from AudioOutputStream.
+void AudioSynchronizedStream::SetVolume(double volume) {}
+void AudioSynchronizedStream::GetVolume(double* volume) {}
+
+OSStatus AudioSynchronizedStream::SetOutputDeviceAsCurrent(
+    AudioDeviceID output_id) {
+  OSStatus result = noErr;
+
+  // Get the default output device if device is unknown.
+  if (output_id == kAudioDeviceUnknown) {
+    AudioObjectPropertyAddress pa;
+    pa.mSelector = kAudioHardwarePropertyDefaultOutputDevice;
+    pa.mScope = kAudioObjectPropertyScopeGlobal;
+    pa.mElement = kAudioObjectPropertyElementMaster;
+    UInt32 size = sizeof(output_id);
+
+    result = AudioObjectGetPropertyData(
+        kAudioObjectSystemObject,
+        &pa,
+        0,
+        0,
+        &size,
+        &output_id);
+
+    OSSTATUS_DCHECK(result == noErr, result);
+    if (result != noErr)
+      return result;
+  }
+
+  // Set the render frame size.
+  UInt32 frame_size = hardware_buffer_size_;
+  AudioObjectPropertyAddress pa;
+  pa.mSelector = kAudioDevicePropertyBufferFrameSize;
+  pa.mScope = kAudioDevicePropertyScopeInput;
+  pa.mElement = kAudioObjectPropertyElementMaster;
+  result = AudioObjectSetPropertyData(
+      output_id,
+      &pa,
+      0,
+      0,
+      sizeof(frame_size),
+      &frame_size);
+
+  OSSTATUS_DCHECK(result == noErr, result);
+  if (result != noErr)
+    return result;
+
+  output_info_.Initialize(output_id, false);
+
+  // Set the Current Device to the Default Output Unit.
+  result = AudioUnitSetProperty(
+      output_unit_,
+      kAudioOutputUnitProperty_CurrentDevice,
+      kAudioUnitScope_Global,
+      0,
+      &output_info_.id_,
+      sizeof(output_info_.id_));
+
+  OSSTATUS_DCHECK(result == noErr, result);
+  return result;
+}
+
+OSStatus AudioSynchronizedStream::SetInputDeviceAsCurrent(
+    AudioDeviceID input_id) {
+  OSStatus result = noErr;
+
+  // Get the default input device if device is unknown.
+  if (input_id == kAudioDeviceUnknown) {
+    AudioObjectPropertyAddress pa;
+    pa.mSelector = kAudioHardwarePropertyDefaultInputDevice;
+    pa.mScope = kAudioObjectPropertyScopeGlobal;
+    pa.mElement = kAudioObjectPropertyElementMaster;
+    UInt32 size = sizeof(input_id);
+
+    result = AudioObjectGetPropertyData(
+        kAudioObjectSystemObject,
+        &pa,
+        0,
+        0,
+        &size,
+        &input_id);
+
+    OSSTATUS_DCHECK(result == noErr, result);
+    if (result != noErr)
+      return result;
+  }
+
+  // Set the render frame size.
+  UInt32 frame_size = hardware_buffer_size_;
+  AudioObjectPropertyAddress pa;
+  pa.mSelector = kAudioDevicePropertyBufferFrameSize;
+  pa.mScope = kAudioDevicePropertyScopeInput;
+  pa.mElement = kAudioObjectPropertyElementMaster;
+  result = AudioObjectSetPropertyData(
+      input_id,
+      &pa,
+      0,
+      0,
+      sizeof(frame_size),
+      &frame_size);
+
+  OSSTATUS_DCHECK(result == noErr, result);
+  if (result != noErr)
+    return result;
+
+  input_info_.Initialize(input_id, true);
+
+  // Set the Current Device to the AUHAL.
+  // This should be done only after I/O has been enabled on the AUHAL.
+  result = AudioUnitSetProperty(
+      input_unit_,
+      kAudioOutputUnitProperty_CurrentDevice,
+      kAudioUnitScope_Global,
+      0,
+      &input_info_.id_,
+      sizeof(input_info_.id_));
+
+  OSSTATUS_DCHECK(result == noErr, result);
+  return result;
+}
+
+OSStatus AudioSynchronizedStream::CreateAudioUnits() {
+  // Q: Why do we need a varispeed unit?
+  // A: If the input device and the output device are running at
+  // different sample rates and/or on different clocks, we will need
+  // to compensate to avoid a pitch change and
+  // to avoid buffer under and over runs.
+  ComponentDescription varispeed_desc;
+  varispeed_desc.componentType = kAudioUnitType_FormatConverter;
+  varispeed_desc.componentSubType = kAudioUnitSubType_Varispeed;
+  varispeed_desc.componentManufacturer = kAudioUnitManufacturer_Apple;
+  varispeed_desc.componentFlags = 0;
+  varispeed_desc.componentFlagsMask = 0;
+
+  Component varispeed_comp = FindNextComponent(NULL, &varispeed_desc);
+  if (varispeed_comp == NULL)
+    return -1;
+
+  OSStatus result = OpenAComponent(varispeed_comp, &varispeed_unit_);
+  OSSTATUS_DCHECK(result == noErr, result);
+  if (result != noErr)
+    return result;
+
+  // Open input AudioUnit.
+  ComponentDescription input_desc;
+  input_desc.componentType = kAudioUnitType_Output;
+  input_desc.componentSubType = kAudioUnitSubType_HALOutput;
+  input_desc.componentManufacturer = kAudioUnitManufacturer_Apple;
+  input_desc.componentFlags = 0;
+  input_desc.componentFlagsMask = 0;
+
+  Component input_comp = FindNextComponent(NULL, &input_desc);
+  if (input_comp == NULL)
+    return -1;
+
+  result = OpenAComponent(input_comp, &input_unit_);
+  OSSTATUS_DCHECK(result == noErr, result);
+  if (result != noErr)
+    return result;
+
+  // Open output AudioUnit.
+  ComponentDescription output_desc;
+  output_desc.componentType = kAudioUnitType_Output;
+  output_desc.componentSubType = kAudioUnitSubType_DefaultOutput;
+  output_desc.componentManufacturer = kAudioUnitManufacturer_Apple;
+  output_desc.componentFlags = 0;
+  output_desc.componentFlagsMask = 0;
+
+  Component output_comp = FindNextComponent(NULL, &output_desc);
+  if (output_comp == NULL)
+    return -1;
+
+  result = OpenAComponent(output_comp, &output_unit_);
+  OSSTATUS_DCHECK(result == noErr, result);
+  if (result != noErr)
+    return result;
+
+  return noErr;
+}
+
+OSStatus AudioSynchronizedStream::SetupInput(AudioDeviceID input_id) {
+  // The AUHAL used for input needs to be initialized
+  // before anything is done to it.
+  OSStatus result = AudioUnitInitialize(input_unit_);
+  OSSTATUS_DCHECK(result == noErr, result);
+  if (result != noErr)
+    return result;
+
+  // We must enable the Audio Unit (AUHAL) for input and disable output
+  // BEFORE setting the AUHAL's current device.
+  result = EnableIO();
+  OSSTATUS_DCHECK(result == noErr, result);
+  if (result != noErr)
+    return result;
+
+  result = SetInputDeviceAsCurrent(input_id);
+  OSSTATUS_DCHECK(result == noErr, result);
+
+  return result;
+}
+
+OSStatus AudioSynchronizedStream::EnableIO() {
+  // Enable input on the AUHAL.
+  UInt32 enable_io = 1;
+  OSStatus result = AudioUnitSetProperty(
+      input_unit_,
+      kAudioOutputUnitProperty_EnableIO,
+      kAudioUnitScope_Input,
+      1,  // input element
+      &enable_io,
+      sizeof(enable_io));
+
+  OSSTATUS_DCHECK(result == noErr, result);
+  if (result != noErr)
+    return result;
+
+  // Disable Output on the AUHAL.
+  enable_io = 0;
+  result = AudioUnitSetProperty(
+      input_unit_,
+      kAudioOutputUnitProperty_EnableIO,
+      kAudioUnitScope_Output,
+      0,  // output element
+      &enable_io,
+      sizeof(enable_io));
+
+  OSSTATUS_DCHECK(result == noErr, result);
+  return result;
+}
+
+OSStatus AudioSynchronizedStream::SetupOutput(AudioDeviceID output_id) {
+  OSStatus result = noErr;
+
+  result = SetOutputDeviceAsCurrent(output_id);
+  OSSTATUS_DCHECK(result == noErr, result);
+  if (result != noErr)
+    return result;
+
+  // Tell the output unit not to reset timestamps.
+  // Otherwise sample rate changes will cause sync loss.
+  UInt32 start_at_zero = 0;
+  result = AudioUnitSetProperty(
+      output_unit_,
+      kAudioOutputUnitProperty_StartTimestampsAtZero,
+      kAudioUnitScope_Global,
+      0,
+      &start_at_zero,
+      sizeof(start_at_zero));
+
+  OSSTATUS_DCHECK(result == noErr, result);
+
+  return result;
+}
+
+OSStatus AudioSynchronizedStream::SetupCallbacks() {
+  // Set the input callback.
+  AURenderCallbackStruct callback;
+  callback.inputProc = InputProc;
+  callback.inputProcRefCon = this;
+  OSStatus result = AudioUnitSetProperty(
+      input_unit_,
+      kAudioOutputUnitProperty_SetInputCallback,
+      kAudioUnitScope_Global,
+      0,
+      &callback,
+      sizeof(callback));
+
+  OSSTATUS_DCHECK(result == noErr, result);
+  if (result != noErr)
+    return result;
+
+  // Set the output callback.
+  callback.inputProc = OutputProc;
+  callback.inputProcRefCon = this;
+  result = AudioUnitSetProperty(
+      output_unit_,
+      kAudioUnitProperty_SetRenderCallback,
+      kAudioUnitScope_Input,
+      0,
+      &callback,
+      sizeof(callback));
+
+  OSSTATUS_DCHECK(result == noErr, result);
+  if (result != noErr)
+    return result;
+
+  // Set the varispeed callback.
+  callback.inputProc = VarispeedProc;
+  callback.inputProcRefCon = this;
+  result = AudioUnitSetProperty(
+      varispeed_unit_,
+      kAudioUnitProperty_SetRenderCallback,
+      kAudioUnitScope_Input,
+      0,
+      &callback,
+      sizeof(callback));
+
+  OSSTATUS_DCHECK(result == noErr, result);
+
+  return result;
+}
+
+OSStatus AudioSynchronizedStream::SetupStreamFormats() {
+  AudioStreamBasicDescription asbd, asbd_dev1_in, asbd_dev2_out;
+
+  // Get the Stream Format (Output client side).
+  UInt32 property_size = sizeof(asbd_dev1_in);
+  OSStatus result = AudioUnitGetProperty(
+      input_unit_,
+      kAudioUnitProperty_StreamFormat,
+      kAudioUnitScope_Input,
+      1,
+      &asbd_dev1_in,
+      &property_size);
+
+  OSSTATUS_DCHECK(result == noErr, result);
+  if (result != noErr)
+    return result;
+
+  // Get the Stream Format (client side).
+  property_size = sizeof(asbd);
+  result = AudioUnitGetProperty(
+      input_unit_,
+      kAudioUnitProperty_StreamFormat,
+      kAudioUnitScope_Output,
+      1,
+      &asbd,
+      &property_size);
+
+  OSSTATUS_DCHECK(result == noErr, result);
+  if (result != noErr)
+    return result;
+
+  // Get the Stream Format (Output client side).
+  property_size = sizeof(asbd_dev2_out);
+  result = AudioUnitGetProperty(
+      output_unit_,
+      kAudioUnitProperty_StreamFormat,
+      kAudioUnitScope_Output,
+      0,
+      &asbd_dev2_out,
+      &property_size);
+
+  OSSTATUS_DCHECK(result == noErr, result);
+  if (result != noErr)
+    return result;
+
+  // Set the format of all the AUs to the input/output devices channel count.
+  // For a simple case, you want to set this to
+  // the lower of count of the channels in the input device vs output device.
+  asbd.mChannelsPerFrame = std::min(asbd_dev1_in.mChannelsPerFrame,
+                                    asbd_dev2_out.mChannelsPerFrame);
+
+  // We must get the sample rate of the input device and set it to the
+  // stream format of AUHAL.
+  Float64 rate = 0;
+  property_size = sizeof(rate);
+
+  AudioObjectPropertyAddress pa;
+  pa.mSelector = kAudioDevicePropertyNominalSampleRate;
+  pa.mScope = kAudioObjectPropertyScopeWildcard;
+  pa.mElement = kAudioObjectPropertyElementMaster;
+  result = AudioObjectGetPropertyData(
+      input_info_.id_,
+      &pa,
+      0,
+      0,
+      &property_size,
+      &rate);
+
+  OSSTATUS_DCHECK(result == noErr, result);
+  if (result != noErr)
+    return result;
+
+  input_sample_rate_ = rate;
+
+  asbd.mSampleRate = rate;
+  property_size = sizeof(asbd);
+
+  // Set the new formats to the AUs...
+  result = AudioUnitSetProperty(
+      input_unit_,
+      kAudioUnitProperty_StreamFormat,
+      kAudioUnitScope_Output,
+      1,
+      &asbd,
+      property_size);
+
+  OSSTATUS_DCHECK(result == noErr, result);
+  if (result != noErr)
+    return result;
+
+  result = AudioUnitSetProperty(
+      varispeed_unit_,
+      kAudioUnitProperty_StreamFormat,
+      kAudioUnitScope_Input,
+      0,
+      &asbd,
+      property_size);
+
+  OSSTATUS_DCHECK(result == noErr, result);
+  if (result != noErr)
+    return result;
+
+  // Set the correct sample rate for the output device,
+  // but keep the channel count the same.
+  property_size = sizeof(rate);
+
+  pa.mSelector = kAudioDevicePropertyNominalSampleRate;
+  pa.mScope = kAudioObjectPropertyScopeWildcard;
+  pa.mElement = kAudioObjectPropertyElementMaster;
+  result = AudioObjectGetPropertyData(
+      output_info_.id_,
+      &pa,
+      0,
+      0,
+      &property_size,
+      &rate);
+
+  OSSTATUS_DCHECK(result == noErr, result);
+  if (result != noErr)
+    return result;
+
+  output_sample_rate_ = rate;
+
+  // The requested sample-rate must match the hardware sample-rate.
+  if (output_sample_rate_ != params_.sample_rate()) {
+    LOG(ERROR) << "Requested sample-rate: " << params_.sample_rate()
+        <<  " must match the hardware sample-rate: " << output_sample_rate_;
+    return kAudioDeviceUnsupportedFormatError;
+  }
+
+  asbd.mSampleRate = rate;
+  property_size = sizeof(asbd);
+
+  // Set the new audio stream formats for the rest of the AUs...
+  result = AudioUnitSetProperty(
+      varispeed_unit_,
+      kAudioUnitProperty_StreamFormat,
+      kAudioUnitScope_Output,
+      0,
+      &asbd,
+      property_size);
+
+  OSSTATUS_DCHECK(result == noErr, result);
+  if (result != noErr)
+    return result;
+
+  result = AudioUnitSetProperty(
+      output_unit_,
+      kAudioUnitProperty_StreamFormat,
+      kAudioUnitScope_Input,
+      0,
+      &asbd,
+      property_size);
+
+  OSSTATUS_DCHECK(result == noErr, result);
+  return result;
+}
+
+void AudioSynchronizedStream::AllocateInputData() {
+  // Allocate storage for the AudioBufferList used for the
+  // input data from the input AudioUnit.
+  // We allocate enough space for with one AudioBuffer per channel.
+  size_t malloc_size = offsetof(AudioBufferList, mBuffers[0]) +
+      (sizeof(AudioBuffer) * channels_);
+
+  input_buffer_list_ = static_cast<AudioBufferList*>(malloc(malloc_size));
+  input_buffer_list_->mNumberBuffers = channels_;
+
+  input_bus_ = AudioBus::Create(channels_, hardware_buffer_size_);
+  wrapper_bus_ = AudioBus::CreateWrapper(channels_);
+
+  // Allocate buffers for AudioBufferList.
+  UInt32 buffer_size_bytes = input_bus_->frames() * sizeof(Float32);
+  for (size_t i = 0; i < input_buffer_list_->mNumberBuffers; ++i) {
+    input_buffer_list_->mBuffers[i].mNumberChannels = 1;
+    input_buffer_list_->mBuffers[i].mDataByteSize = buffer_size_bytes;
+    input_buffer_list_->mBuffers[i].mData = input_bus_->channel(i);
+  }
+}
+
+OSStatus AudioSynchronizedStream::HandleInputCallback(
+    AudioUnitRenderActionFlags* io_action_flags,
+    const AudioTimeStamp* time_stamp,
+    UInt32 bus_number,
+    UInt32 number_of_frames,
+    AudioBufferList* io_data) {
+  TRACE_EVENT0("audio", "AudioSynchronizedStream::HandleInputCallback");
+
+  if (first_input_time_ < 0.0)
+    first_input_time_ = time_stamp->mSampleTime;
+
+  // Get the new audio input data.
+  OSStatus result = AudioUnitRender(
+      input_unit_,
+      io_action_flags,
+      time_stamp,
+      bus_number,
+      number_of_frames,
+      input_buffer_list_);
+
+  OSSTATUS_DCHECK(result == noErr, result);
+  if (result != noErr)
+    return result;
+
+  // Buffer input into FIFO.
+  int available_frames = fifo_.max_frames() - fifo_.frames();
+  if (input_bus_->frames() <= available_frames)
+    fifo_.Push(input_bus_.get());
+
+  return result;
+}
+
+OSStatus AudioSynchronizedStream::HandleVarispeedCallback(
+    AudioUnitRenderActionFlags* io_action_flags,
+    const AudioTimeStamp* time_stamp,
+    UInt32 bus_number,
+    UInt32 number_of_frames,
+    AudioBufferList* io_data) {
+  // Create a wrapper bus on the AudioBufferList.
+  WrapBufferList(io_data, wrapper_bus_.get(), number_of_frames);
+
+  if (fifo_.frames() < static_cast<int>(number_of_frames)) {
+    // We don't DCHECK here, since this is a possible run-time condition
+    // if the machine is bogged down.
+    wrapper_bus_->Zero();
+    return noErr;
+  }
+
+  // Read from the FIFO to feed the varispeed.
+  fifo_.Consume(wrapper_bus_.get(), 0, number_of_frames);
+
+  return noErr;
+}
+
+OSStatus AudioSynchronizedStream::HandleOutputCallback(
+    AudioUnitRenderActionFlags* io_action_flags,
+    const AudioTimeStamp* time_stamp,
+    UInt32 bus_number,
+    UInt32 number_of_frames,
+    AudioBufferList* io_data) {
+  if (first_input_time_ < 0.0) {
+    // Input callback hasn't run yet -> silence.
+    ZeroBufferList(io_data);
+    return noErr;
+  }
+
+  // Use the varispeed playback rate to offset small discrepancies
+  // in hardware clocks, and also any differences in sample-rate
+  // between input and output devices.
+
+  // Calculate a varispeed rate scalar factor to compensate for drift between
+  // input and output.  We use the actual number of frames still in the FIFO
+  // compared with the ideal value of |target_fifo_frames_|.
+  int delta = fifo_.frames() - target_fifo_frames_;
+
+  // Average |delta| because it can jitter back/forth quite frequently
+  // by +/- the hardware buffer-size *if* the input and output callbacks are
+  // happening at almost exactly the same time.  Also, if the input and output
+  // sample-rates are different then |delta| will jitter quite a bit due to
+  // the rate conversion happening in the varispeed, plus the jittering of
+  // the callbacks.  The average value is what's important here.
+  average_delta_ += (delta - average_delta_) * 0.1;
+
+  // Compute a rate compensation which always attracts us back to the
+  // |target_fifo_frames_| over a period of kCorrectionTimeSeconds.
+  const double kCorrectionTimeSeconds = 0.1;
+  double correction_time_frames = kCorrectionTimeSeconds * output_sample_rate_;
+  fifo_rate_compensation_ =
+      (correction_time_frames + average_delta_) / correction_time_frames;
+
+  // Adjust for FIFO drift.
+  OSStatus result = AudioUnitSetParameter(
+      varispeed_unit_,
+      kVarispeedParam_PlaybackRate,
+      kAudioUnitScope_Global,
+      0,
+      fifo_rate_compensation_,
+      0);
+
+  OSSTATUS_DCHECK(result == noErr, result);
+  if (result != noErr)
+    return result;
+
+  // Render to the output using the varispeed.
+  result = AudioUnitRender(
+      varispeed_unit_,
+      io_action_flags,
+      time_stamp,
+      0,
+      number_of_frames,
+      io_data);
+
+  OSSTATUS_DCHECK(result == noErr, result);
+  if (result != noErr)
+    return result;
+
+  // Create a wrapper bus on the AudioBufferList.
+  WrapBufferList(io_data, wrapper_bus_.get(), number_of_frames);
+
+  // Process in-place!
+  source_->OnMoreIOData(wrapper_bus_.get(),
+                        wrapper_bus_.get(),
+                        AudioBuffersState(0, 0));
+
+  return noErr;
+}
+
+OSStatus AudioSynchronizedStream::InputProc(
+    void* user_data,
+    AudioUnitRenderActionFlags* io_action_flags,
+    const AudioTimeStamp* time_stamp,
+    UInt32 bus_number,
+    UInt32 number_of_frames,
+    AudioBufferList* io_data) {
+  AudioSynchronizedStream* stream =
+      static_cast<AudioSynchronizedStream*>(user_data);
+  DCHECK(stream);
+
+  return stream->HandleInputCallback(
+      io_action_flags,
+      time_stamp,
+      bus_number,
+      number_of_frames,
+      io_data);
+}
+
+OSStatus AudioSynchronizedStream::VarispeedProc(
+    void* user_data,
+    AudioUnitRenderActionFlags* io_action_flags,
+    const AudioTimeStamp* time_stamp,
+    UInt32 bus_number,
+    UInt32 number_of_frames,
+    AudioBufferList* io_data) {
+  AudioSynchronizedStream* stream =
+      static_cast<AudioSynchronizedStream*>(user_data);
+  DCHECK(stream);
+
+  return stream->HandleVarispeedCallback(
+      io_action_flags,
+      time_stamp,
+      bus_number,
+      number_of_frames,
+      io_data);
+}
+
+OSStatus AudioSynchronizedStream::OutputProc(
+    void* user_data,
+    AudioUnitRenderActionFlags* io_action_flags,
+    const AudioTimeStamp* time_stamp,
+    UInt32 bus_number,
+    UInt32 number_of_frames,
+    AudioBufferList* io_data) {
+  AudioSynchronizedStream* stream =
+      static_cast<AudioSynchronizedStream*>(user_data);
+  DCHECK(stream);
+
+  return stream->HandleOutputCallback(
+      io_action_flags,
+      time_stamp,
+      bus_number,
+      number_of_frames,
+      io_data);
+}
+
+void AudioSynchronizedStream::AudioDeviceInfo::Initialize(
+    AudioDeviceID id, bool is_input) {
+  id_ = id;
+  is_input_ = is_input;
+  if (id_ == kAudioDeviceUnknown)
+    return;
+
+  UInt32 property_size = sizeof(buffer_size_frames_);
+
+  AudioObjectPropertyAddress pa;
+  pa.mSelector = kAudioDevicePropertyBufferFrameSize;
+  pa.mScope = kAudioObjectPropertyScopeWildcard;
+  pa.mElement = kAudioObjectPropertyElementMaster;
+  OSStatus result = AudioObjectGetPropertyData(
+      id_,
+      &pa,
+      0,
+      0,
+      &property_size,
+      &buffer_size_frames_);
+
+  OSSTATUS_DCHECK(result == noErr, result);
+}
+
+}  // namespace media