[Chromecast] Reduce memory allocation/free on mixer thread

Bug: internal b/137439407
Change-Id: Ia316552cfd0d884f1c55ce32603b426778f08cae
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1715765Reviewed-by: Sergey Volk <servolk@chromium.org>
Commit-Queue: Kenneth MacKay <kmackay@chromium.org>
Cr-Commit-Position: refs/heads/master@{#680584}

chromecast/media/cma/backend/BUILD.gn

@@ -121,6 +121,7 @@ cast_source_set("audio_helpers") {
 
   deps = [
     "//base",
+    "//chromecast/public/media",
     "//media",
   ]
 }
@@ -240,6 +241,8 @@ cast_source_set("for_mixer_audio") {
     "cast_media_shlib_mixer_audio.cc",
     "direct_mixer_source.cc",
     "direct_mixer_source.h",
+    "loopback_handler.cc",
+    "loopback_handler.h",
     "media_pipeline_backend_for_mixer.cc",
     "media_pipeline_backend_for_mixer.h",
     "stream_mixer.cc",

chromecast/media/cma/backend/audio_fader.h

@@ -5,9 +5,12 @@
 #ifndef CHROMECAST_MEDIA_CMA_BACKEND_AUDIO_FADER_H_
 #define CHROMECAST_MEDIA_CMA_BACKEND_AUDIO_FADER_H_
 
+#include <cstdint>
 #include <memory>
 
 #include "base/macros.h"
+#include "base/time/time.h"
+#include "chromecast/public/media/media_pipeline_backend.h"
 
 namespace media {
 class AudioBus;
@@ -24,57 +27,67 @@ namespace media {
 // constructor/destructor must be called on the same thread.
 class AudioFader {
  public:
+  using RenderingDelay = MediaPipelineBackend::AudioDecoder::RenderingDelay;
+
   // The source of real audio data for the fader.
   class Source {
    public:
-    // Fills at most |num_frames| frames of audio into |buffer|, starting at
-    // |frame_offset|. Returns the actual number of frames of audio that were
-    // filled (may be less than |num_frames| if the source does not have
-    // enough data). This method is only called synchronously from within
-    // a call to FillFrames().
-    virtual int FillFaderFrames(::media::AudioBus* buffer,
-                                int frame_offset,
-                                int num_frames) = 0;
+    // Called to get more audio data for playback. The source must fill in
+    // the |channels| with up to |num_frames| of audio. Note that only planar
+    // float format is supported. The |rendering_delay| indicates when the
+    // first frame of the filled data will be played out.
+    // Note that this method is called on a high priority audio output thread
+    // and must not block.
+    // Returns the number of frames filled.
+    virtual int FillFaderFrames(int num_frames,
+                                RenderingDelay rendering_delay,
+                                float* const* channels) = 0;
 
    protected:
     virtual ~Source() = default;
   };
 
-  // |fade_frames| is the number of frames over which a complete fade in/out
-  // will take place.
-  AudioFader(Source* source, int num_channels, int fade_frames);
+  AudioFader(Source* source,
+             base::TimeDelta fade_time,
+             int num_channels,
+             int sample_rate,
+             double playback_rate);
+  AudioFader(Source* source,
+             int fade_frames,
+             int num_channels,
+             int sample_rate,
+             double playback_rate);
   ~AudioFader();
 
   int buffered_frames() const { return buffered_frames_; }
 
-  // Fills |buffer| with up to |num_frames| frames of data, starting at
-  // |write_offset| within |buffer|, and fading as appropriate to avoid
-  // pops/clicks. This will call through to the source to get more data. Returns
-  // the number of frames filled.
-  int FillFrames(int num_frames, ::media::AudioBus* buffer, int write_offset);
+  // Fills in |channel_data| with |num_frames| frames of properly faded audio.
+  // The |rendering_delay| should reflect when the first sample of the filled
+  // audio is expected to play out.
+  int FillFrames(int num_frames,
+                 RenderingDelay rendering_delay,
+                 float* const* channel_data);
 
   // Returns the total number of frames that will be requested from the source
   // (potentially over multiple calls to source_->FillFaderFrames()) if
   // FillFrames() is called to fill |num_fill_frames| frames.
   int FramesNeededFromSource(int num_fill_frames) const;
 
-  // Helper methods to fade in/out an AudioBus. |buffer| contains the data to
-  // fade; |filled_frames| is the amount of data actually in |buffer| (if the
-  // buffer was partially filled, this will not be equal to buffer->frames()).
-  // |write_offset| is the offset within |buffer| to starting writing frames
-  // to. |fade_frames| is the number of frames over which a complete fade should
+  // Helper methods to fade in/out a buffer. |channel_data| contains the data to
+  // fade; |filled_frames| is the amount of data actually in |channel_data|.
+  // |fade_frames| is the number of frames over which a complete fade should
   // happen (ie, how many frames it takes to go from a 1.0 to 0.0 multiplier).
   // |fade_frames_remaining| is the number of frames left in the current fade
   // (which will be less than |fade_frames| if part of the fade has already
   // been completed on a previous buffer).
-  static void FadeInHelper(::media::AudioBus* buffer,
+  static void FadeInHelper(float* const* channel_data,
+                           int num_channels,
                            int filled_frames,
-                           int write_offset,
                            int fade_frames,
                            int fade_frames_remaining);
-  static void FadeOutHelper(::media::AudioBus* buffer,
+  static void FadeOutHelper(float* const* channel_data,
+                            int num_channels,
                             int filled_frames,
-                            int write_offset,
                             int fade_frames,
                             int fade_frames_remaining);
 
@@ -86,22 +99,23 @@ class AudioFader {
     kFadingOut,
   };
 
-  void CompleteFill(::media::AudioBus* buffer,
-                    int filled_frames,
-                    int write_offset);
-  void IncompleteFill(::media::AudioBus* buffer,
-                      int filled_frames,
-                      int write_offset);
-  void FadeIn(::media::AudioBus* buffer, int filled_frames, int write_offset);
-  void FadeOut(::media::AudioBus* buffer, int filled_frames, int write_offset);
+  int64_t FramesToMicroseconds(int64_t frames);
+
+  void CompleteFill(float* const* channel_data, int filled_frames);
+  void IncompleteFill(float* const* channel_data, int filled_frames);
+  void FadeIn(float* const* channel_data, int filled_frames);
+  void FadeOut(float* const* channel_data, int filled_frames);
 
   Source* const source_;
   const int fade_frames_;
+  const int num_channels_;
+  const int sample_rate_;
+  const double playback_rate_;
 
-  State state_;
+  State state_ = State::kSilent;
   std::unique_ptr<::media::AudioBus> fade_buffer_;
-  int buffered_frames_;
-  int fade_frames_remaining_;
+  int buffered_frames_ = 0;
+  int fade_frames_remaining_ = 0;
 
   DISALLOW_COPY_AND_ASSIGN(AudioFader);
 };

chromecast/media/cma/backend/audio_output_redirector.cc

@@ -22,6 +22,10 @@
 namespace chromecast {
 namespace media {
 
+namespace {
+const int kDefaultBufferSize = 2048;
+}  // namespace
+
 class AudioOutputRedirector::InputImpl : public AudioOutputRedirectorInput {
  public:
   using RenderingDelay = MediaPipelineBackend::AudioDecoder::RenderingDelay;
@@ -59,6 +63,10 @@ AudioOutputRedirector::InputImpl::InputImpl(
   DCHECK(output_redirector_);
   DCHECK(mixer_input_);
 
+  temp_buffer_ = ::media::AudioBus::Create(mixer_input_->num_channels(),
+                                           kDefaultBufferSize);
+  temp_buffer_->Zero();
+
   mixer_input_->AddAudioOutputRedirector(this);
 }
 
@@ -84,16 +92,21 @@ void AudioOutputRedirector::InputImpl::Redirect(::media::AudioBus* const buffer,
       buffer->CopyPartialFramesTo(0, num_frames, 0, temp_buffer_.get());
     }
 
+    const int num_channels = buffer->channels();
+    float* channels[num_channels];
+    for (int c = 0; c < num_channels; ++c) {
+      channels[c] = buffer->channel(c);
+    }
     if (previous_ended_in_silence_) {
       if (!redirected) {
         // Smoothly fade in from previous silence.
-        AudioFader::FadeInHelper(temp_buffer_.get(), num_frames, 0, num_frames,
+        AudioFader::FadeInHelper(channels, num_channels, num_frames, num_frames,
                                  num_frames);
       }
     } else if (redirected) {
       // Smoothly fade out to silence, since output is now being redirected by a
       // previous output splitter.
-      AudioFader::FadeOutHelper(temp_buffer_.get(), num_frames, 0, num_frames,
+      AudioFader::FadeOutHelper(channels, num_channels, num_frames, num_frames,
                                 num_frames);
     }
     previous_ended_in_silence_ = redirected;
@@ -111,6 +124,13 @@ AudioOutputRedirector::AudioOutputRedirector(
       channel_data_(config.num_output_channels) {
   DCHECK(output_);
   DCHECK_GT(config_.num_output_channels, 0);
+
+  mixed_ = ::media::AudioBus::Create(config_.num_output_channels,
+                                     kDefaultBufferSize);
+  mixed_->Zero();
+  for (int c = 0; c < config_.num_output_channels; ++c) {
+    channel_data_[c] = mixed_->channel(c);
+  }
 }
 
 AudioOutputRedirector::~AudioOutputRedirector() = default;

chromecast/media/cma/backend/buffering_mixer_source.h

@@ -7,6 +7,7 @@
 
 #include <string>
 
+#include "base/callback.h"
 #include "base/containers/circular_deque.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
@@ -147,8 +148,13 @@ class BufferingMixerSource : public MixerInput::Source,
       bool mixer_error_ = false;
       scoped_refptr<DecoderBufferBase> pending_data_;
       base::circular_deque<scoped_refptr<DecoderBufferBase>> queue_;
+      // We let the caller thread free audio buffers since freeing memory can
+      // be expensive sometimes; we want to avoid potentially long-running
+      // operations on the mixer thread.
+      std::vector<scoped_refptr<DecoderBufferBase>> buffers_to_be_freed_;
       int queued_frames_ = 0;
       RenderingDelay mixer_rendering_delay_;
+      RenderingDelay last_buffer_delay_;
       int extra_delay_frames_ = 0;
       int current_buffer_offset_ = 0;
       AudioFader fader_;
@@ -229,13 +235,13 @@ class BufferingMixerSource : public MixerInput::Source,
   void FinalizeAudioPlayback() override;
 
   // AudioFader::Source implementation:
-  int FillFaderFrames(::media::AudioBus* dest,
-                      int frame_offset,
-                      int num_frames) override;
+  int FillFaderFrames(int num_frames,
+                      RenderingDelay rendering_delay,
+                      float* const* channels) override;
 
   RenderingDelay QueueData(scoped_refptr<DecoderBufferBase> data);
 
-  void PostPcmCompletion(RenderingDelay delay);
+  void PostPcmCompletion();
   void PostEos();
   void PostError(MixerError error);
   void PostAudioReadyForPlayback();
@@ -257,10 +263,17 @@ class BufferingMixerSource : public MixerInput::Source,
   const int start_threshold_frames_;
   bool audio_ready_for_playback_fired_ = false;
 
+  // Only used on the caller thread.
+  std::vector<scoped_refptr<DecoderBufferBase>> old_buffers_to_be_freed_;
+
   LockedMembers locked_members_;
 
   int remaining_silence_frames_ = 0;
 
+  base::RepeatingClosure pcm_completion_task_;
+  base::RepeatingClosure eos_task_;
+  base::RepeatingClosure ready_for_playback_task_;
+
   base::WeakPtr<BufferingMixerSource> weak_this_;
   base::WeakPtrFactory<BufferingMixerSource> weak_factory_;
 

chromecast/media/cma/backend/filter_group.cc

@@ -62,6 +62,7 @@ void FilterGroup::Initialize(const AudioPostProcessor2::Config& output_config) {
   ResizeBuffers();
 
   // Run a buffer of 0's to initialize rendering delay.
+  std::fill_n(interleaved_.data(), interleaved_.size(), 0.0f);
   delay_seconds_ = post_processing_pipeline_->ProcessFrames(
       interleaved_.data(), input_frames_per_write_, last_volume_,
       true /* is_silence */);
@@ -203,6 +204,7 @@ int FilterGroup::GetOutputChannelCount() const {
 
 void FilterGroup::ResizeBuffers() {
   mixed_ = ::media::AudioBus::Create(num_channels_, input_frames_per_write_);
+  mixed_->Zero();
   temp_buffers_.clear();
   for (MixerInput* input : active_inputs_) {
     AddTempBuffer(input->num_channels(), input_frames_per_write_);
@@ -217,6 +219,7 @@ void FilterGroup::AddTempBuffer(int num_channels, int num_frames) {
   if (!temp_buffers_[num_channels]) {
     temp_buffers_[num_channels] =
         ::media::AudioBus::Create(num_channels, num_frames);
+    temp_buffers_[num_channels]->Zero();
   }
 }
 

chromecast/media/cma/backend/loopback_handler.cc

+// Copyright 2019 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 "chromecast/media/cma/backend/loopback_handler.h"
+
+#include <algorithm>
+#include <utility>
+#include <vector>
+
+#include "base/bind.h"
+#include "base/containers/flat_set.h"
+#include "base/location.h"
+#include "base/logging.h"
+#include "base/single_thread_task_runner.h"
+#include "base/synchronization/condition_variable.h"
+#include "base/synchronization/lock.h"
+#include "base/thread_annotations.h"
+#include "base/threading/thread.h"
+#include "chromecast/public/media/external_audio_pipeline_shlib.h"
+
+namespace chromecast {
+namespace media {
+
+namespace {
+
+const int kDefaultBufferSize = 1024 * 2 * sizeof(float);
+const int kNumBuffers = 16;
+const int kMaxTasks = kNumBuffers + 1;
+
+class LoopbackHandlerImpl : public LoopbackHandler,
+                            public CastMediaShlib::LoopbackAudioObserver {
+ public:
+  LoopbackHandlerImpl(scoped_refptr<base::SingleThreadTaskRunner> task_runner)
+      : external_audio_pipeline_supported_(
+            ExternalAudioPipelineShlib::IsSupported()),
+        task_signal_(&lock_) {
+    CreateBuffersIfNeeded(kDefaultBufferSize);
+
+    if (task_runner) {
+      task_runner_ = std::move(task_runner);
+    } else {
+      thread_ = std::make_unique<base::Thread>("CMA loopback");
+      base::Thread::Options options;
+      options.priority = base::ThreadPriority::REALTIME_AUDIO;
+      thread_->StartWithOptions(options);
+      task_runner_ = thread_->task_runner();
+
+      task_runner_->PostTask(
+          FROM_HERE, base::BindOnce(&LoopbackHandlerImpl::LoopbackTaskLoop,
+                                    base::Unretained(this)));
+    }
+
+    if (external_audio_pipeline_supported_) {
+      ExternalAudioPipelineShlib::AddExternalLoopbackAudioObserver(this);
+    }
+  }
+
+ private:
+  struct Task {
+    Task(int64_t expected_playback_time,
+         SampleFormat format,
+         int sample_rate,
+         int channels,
+         uint32_t tag,
+         std::unique_ptr<uint8_t[]> data,
+         int length)
+        : expected_playback_time(expected_playback_time),
+          format(format),
+          sample_rate(sample_rate),
+          channels(channels),
+          tag(tag),
+          data(std::move(data)),
+          length(length) {}
+
+    const int64_t expected_playback_time;
+    const SampleFormat format;
+    const int sample_rate;
+    const int channels;
+    const uint32_t tag;
+    std::unique_ptr<uint8_t[]> data;
+    const int length;
+  };
+
+  ~LoopbackHandlerImpl() override {
+    {
+      base::AutoLock lock(lock_);
+      stop_thread_ = true;
+    }
+    task_signal_.Signal();
+    if (thread_) {
+      thread_->Stop();
+    }
+  }
+
+  // LoopbackHandler implementation:
+  void Destroy() override {
+    if (external_audio_pipeline_supported_) {
+      ExternalAudioPipelineShlib::RemoveExternalLoopbackAudioObserver(this);
+    } else {
+      delete this;
+    }
+  }
+
+  void SetDataSize(int data_size_bytes) override {
+    CreateBuffersIfNeeded(data_size_bytes);
+  }
+
+  scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunner() override {
+    return task_runner_;
+  }
+
+  void AddObserver(CastMediaShlib::LoopbackAudioObserver* observer) override {
+    task_runner_->PostTask(
+        FROM_HERE, base::BindOnce(&LoopbackHandlerImpl::AddObserverOnThread,
+                                  base::Unretained(this), observer));
+    task_signal_.Signal();
+  }
+
+  void RemoveObserver(
+      CastMediaShlib::LoopbackAudioObserver* observer) override {
+    task_runner_->PostTask(
+        FROM_HERE, base::BindOnce(&LoopbackHandlerImpl::RemoveObserverOnThread,
+                                  base::Unretained(this), observer));
+    task_signal_.Signal();
+  }
+
+  void SendData(int64_t timestamp,
+                int sample_rate,
+                int num_channels,
+                float* data,
+                int frames) override {
+    if (external_audio_pipeline_supported_) {
+      return;
+    }
+
+    SendLoopbackData(timestamp, kSampleFormatF32, sample_rate, num_channels,
+                     reinterpret_cast<uint8_t*>(data),
+                     frames * num_channels * sizeof(float));
+  }
+
+  void SendInterrupt() override {
+    base::AutoLock lock(lock_);
+    SendInterruptedLocked();
+  }
+
+  // CastMediaShlib::LoopbackAudioObserver implementation:
+  void OnLoopbackAudio(int64_t timestamp,
+                       SampleFormat format,
+                       int sample_rate,
+                       int num_channels,
+                       uint8_t* data,
+                       int length) override {
+    SendLoopbackData(timestamp, format, sample_rate, num_channels, data,
+                     length);
+  }
+
+  void OnLoopbackInterrupted() override { SendInterrupt(); }
+
+  void OnRemoved() override {
+    // We expect that external pipeline will not invoke any other callbacks
+    // after this one.
+    delete this;
+    // No need to pipe this, LoopbackHandlerImpl will let the other observer
+    // know when it's being removed.
+  }
+
+  void AddObserverOnThread(CastMediaShlib::LoopbackAudioObserver* observer) {
+    DCHECK(task_runner_->BelongsToCurrentThread());
+    LOG(INFO) << __func__;
+    DCHECK(observer);
+
+    observers_.insert(observer);
+  }
+
+  void RemoveObserverOnThread(CastMediaShlib::LoopbackAudioObserver* observer) {
+    DCHECK(task_runner_->BelongsToCurrentThread());
+    LOG(INFO) << __func__;
+    DCHECK(observer);
+
+    observers_.erase(observer);
+    observer->OnRemoved();
+  }
+
+  void CreateBuffersIfNeeded(int buffer_size_bytes) {
+    if (buffer_size_bytes <= buffer_size_) {
+      return;
+    }
+    LOG(INFO) << "Create new buffers, size = " << buffer_size_bytes;
+
+    base::AutoLock lock(lock_);
+    ++buffer_tag_;
+    buffers_.clear();
+    for (int i = 0; i < kNumBuffers; ++i) {
+      auto buffer = std::make_unique<uint8_t[]>(buffer_size_bytes);
+      std::fill_n(buffer.get(), buffer_size_bytes, 0);
+      buffers_.push_back(std::move(buffer));
+    }
+    buffer_size_ = buffer_size_bytes;
+
+    tasks_.reserve(kMaxTasks);
+    new_tasks_.reserve(kMaxTasks);
+  }
+
+  void SendLoopbackData(int64_t timestamp,
+                        SampleFormat format,
+                        int sample_rate,
+                        int num_channels,
+                        uint8_t* data,
+                        int length) {
+    CreateBuffersIfNeeded(length);
+
+    {
+      base::AutoLock lock(lock_);
+
+      if (buffers_.empty() || tasks_.size() >= kNumBuffers) {
+        LOG(ERROR) << "Can't send loopback data";
+        SendInterruptedLocked();
+        return;
+      }
+
+      std::unique_ptr<uint8_t[]> buffer = std::move(buffers_.back());
+      buffers_.pop_back();
+
+      std::copy(data, data + length, buffer.get());
+      tasks_.emplace_back(timestamp, format, sample_rate, num_channels,
+                          buffer_tag_, std::move(buffer), length);
+    }
+
+    if (thread_) {
+      task_signal_.Signal();
+    } else {
+      HandleLoopbackTask(&tasks_.back());
+      tasks_.pop_back();
+    }
+  }
+
+  void SendInterruptedLocked() {
+    lock_.AssertAcquired();
+
+    if (tasks_.size() == kMaxTasks) {
+      return;
+    }
+    tasks_.emplace_back(0, kSampleFormatF32, 0, 0, 0, nullptr, 0);
+
+    if (thread_) {
+      task_signal_.Signal();
+    } else {
+      HandleLoopbackTask(&tasks_.back());
+      tasks_.pop_back();
+    }
+  }
+
+  void LoopbackTaskLoop() {
+    DCHECK(task_runner_->BelongsToCurrentThread());
+
+    {
+      base::AutoLock lock(lock_);
+      if (stop_thread_)
+        return;
+      if (tasks_.empty()) {
+        task_signal_.Wait();
+      }
+      new_tasks_.swap(tasks_);
+    }
+
+    for (auto& task : new_tasks_) {
+      HandleLoopbackTask(&task);
+    }
+    new_tasks_.clear();
+
+    task_runner_->PostTask(
+        FROM_HERE, base::BindOnce(&LoopbackHandlerImpl::LoopbackTaskLoop,
+                                  base::Unretained(this)));
+  }
+
+  void HandleLoopbackTask(Task* task) {
+    if (!task->data) {
+      for (auto* observer : observers_) {
+        observer->OnLoopbackInterrupted();
+      }
+      return;
+    }
+
+    for (auto* observer : observers_) {
+      observer->OnLoopbackAudio(task->expected_playback_time, task->format,
+                                task->sample_rate, task->channels,
+                                task->data.get(), task->length);
+    }
+
+    base::AutoLock lock(lock_);
+    if (task->tag == buffer_tag_) {
+      // Only return the buffer if the tag matches. Otherwise, the buffer size
+      // may have changed (so we should just delete the buffer).
+      buffers_.push_back(std::move(task->data));
+    }
+  }
+
+  const bool external_audio_pipeline_supported_;
+
+  std::unique_ptr<base::Thread> thread_;
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+
+  int buffer_size_ = 0;
+
+  base::Lock lock_;
+  uint32_t buffer_tag_ GUARDED_BY(lock_) = 0;
+  std::vector<std::unique_ptr<uint8_t[]>> buffers_ GUARDED_BY(lock_);
+  bool stop_thread_ GUARDED_BY(lock_);
+  base::ConditionVariable task_signal_;
+
+  std::vector<Task> tasks_;
+  std::vector<Task> new_tasks_;
+
+  base::flat_set<CastMediaShlib::LoopbackAudioObserver*> observers_;
+
+  DISALLOW_COPY_AND_ASSIGN(LoopbackHandlerImpl);
+};
+
+}  // namespace
+
+// static
+std::unique_ptr<LoopbackHandler, LoopbackHandler::Deleter>
+LoopbackHandler::Create(
+    scoped_refptr<base::SingleThreadTaskRunner> task_runner) {
+  return std::unique_ptr<LoopbackHandler, LoopbackHandler::Deleter>(
+      new LoopbackHandlerImpl(std::move(task_runner)));
+}
+
+}  // namespace media
+}  // namespace chromecast

chromecast/media/cma/backend/loopback_handler.h

+// Copyright 2019 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.
+
+#ifndef CHROMECAST_MEDIA_CMA_BACKEND_LOOPBACK_HANDLER_H_
+#define CHROMECAST_MEDIA_CMA_BACKEND_LOOPBACK_HANDLER_H_
+
+#include <cstdint>
+#include <memory>
+
+#include "base/memory/scoped_refptr.h"
+#include "chromecast/public/cast_media_shlib.h"
+
+namespace base {
+class SingleThreadTaskRunner;
+}  // namespace base
+
+namespace chromecast {
+namespace media {
+
+// Handles loopback audio from the mixer.
+class LoopbackHandler {
+ public:
+  struct Deleter {
+    void operator()(LoopbackHandler* obj) { obj->Destroy(); }
+  };
+
+  static std::unique_ptr<LoopbackHandler, Deleter> Create(
+      scoped_refptr<base::SingleThreadTaskRunner> task_runner);
+
+  virtual void Destroy() = 0;
+
+  virtual void SetDataSize(int data_size_bytes) = 0;
+
+  virtual scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunner() = 0;
+
+  virtual void AddObserver(CastMediaShlib::LoopbackAudioObserver* observer) = 0;
+  virtual void RemoveObserver(
+      CastMediaShlib::LoopbackAudioObserver* observer) = 0;
+
+  virtual void SendData(int64_t timestamp,
+                        int sample_rate,
+                        int num_channels,
+                        float* data,
+                        int frames) = 0;
+  virtual void SendInterrupt() = 0;
+
+ protected:
+  virtual ~LoopbackHandler() = default;
+};
+
+}  // namespace media
+}  // namespace chromecast
+
+#endif  // CHROMECAST_MEDIA_CMA_BACKEND_LOOPBACK_HANDLER_H_

chromecast/media/cma/backend/mixer_input.cc

@@ -161,6 +161,10 @@ int MixerInput::FillAudioData(int num_frames,
     redirected = true;
   }
 
+  float* channels[num_channels_];
+  for (int c = 0; c < num_channels_; ++c) {
+    channels[c] = dest->channel(c);
+  }
   if (first_buffer_ && redirected) {
     // If the first buffer is redirected, don't provide any data to the mixer
     // (we want to avoid a 'blip' of sound from the first buffer if it is being
@@ -173,11 +177,11 @@ int MixerInput::FillAudioData(int num_frames,
       filled = 0;
     } else {
       // Smoothly fade in from previous silence.
-      AudioFader::FadeInHelper(dest, filled, 0, filled, filled);
+      AudioFader::FadeInHelper(channels, num_channels_, filled, filled, filled);
     }
   } else if (redirected) {
     // Smoothly fade out to silence, since output is now being redirected.
-    AudioFader::FadeOutHelper(dest, filled, 0, filled, filled);
+    AudioFader::FadeOutHelper(channels, num_channels_, filled, filled, filled);
   }
   previous_ended_in_silence_ = redirected;
   first_buffer_ = false;

chromecast/media/cma/backend/stream_mixer.h

@@ -12,6 +12,7 @@
 #include <utility>
 #include <vector>
 
+#include "base/callback.h"
 #include "base/containers/flat_map.h"
 #include "base/containers/flat_set.h"
 #include "base/macros.h"
@@ -20,6 +21,7 @@
 #include "base/single_thread_task_runner.h"
 #include "base/threading/thread.h"
 #include "base/time/time.h"
+#include "chromecast/media/cma/backend/loopback_handler.h"
 #include "chromecast/media/cma/backend/mixer_input.h"
 #include "chromecast/media/cma/backend/mixer_pipeline.h"
 #include "chromecast/public/cast_media_shlib.h"
@@ -124,7 +126,6 @@ class StreamMixer {
   int num_output_channels() const { return num_output_channels_; }
 
  private:
-  class ExternalLoopbackAudioObserver;
   class BaseExternalMediaVolumeChangeRequestObserver
       : public ExternalAudioPipelineShlib::
             ExternalMediaVolumeChangeRequestObserver {
@@ -160,30 +161,15 @@ class StreamMixer {
   void RemoveInputOnThread(MixerInput::Source* input_source);
   void SetCloseTimeout();
   void UpdatePlayoutChannel();
+  void UpdateLoopbackChannelCount();
 
   void PlaybackLoop();
   void WriteOneBuffer();
   void WriteMixedPcm(int frames, int64_t expected_playback_time);
   void MixToMono(float* data, int frames, int channels);
 
-  void RemoveLoopbackAudioObserverOnThread(
-      CastMediaShlib::LoopbackAudioObserver* observer);
   void RemoveAudioOutputRedirectorOnThread(AudioOutputRedirector* redirector);
 
-  void PostLoopbackData(int64_t expected_playback_time,
-                        SampleFormat sample_format,
-                        int sample_rate,
-                        int channels,
-                        std::unique_ptr<uint8_t[]> data,
-                        int length);
-  void PostLoopbackInterrupted();
-
-  void SendLoopbackData(int64_t expected_playback_time,
-                        SampleFormat sample_format,
-                        int sample_rate,
-                        int channels,
-                        std::unique_ptr<uint8_t[]> data,
-                        int length);
   int GetSampleRateForDeviceId(const std::string& device);
 
   MediaPipelineBackend::AudioDecoder::RenderingDelay GetTotalRenderingDelay(
@@ -195,8 +181,7 @@ class StreamMixer {
   std::unique_ptr<MixerPipeline> mixer_pipeline_;
   std::unique_ptr<base::Thread> mixer_thread_;
   scoped_refptr<base::SingleThreadTaskRunner> mixer_task_runner_;
-  std::unique_ptr<base::Thread> loopback_thread_;
-  scoped_refptr<base::SingleThreadTaskRunner> loopback_task_runner_;
+  std::unique_ptr<LoopbackHandler, LoopbackHandler::Deleter> loopback_handler_;
   std::unique_ptr<ThreadHealthChecker> health_checker_;
 
   void OnHealthCheckFailed();
@@ -216,16 +201,16 @@ class StreamMixer {
   int frames_per_write_ = 0;
   int redirector_samples_per_second_ = 0;
   int redirector_frames_per_write_ = 0;
+  int loopback_channel_count_ = 0;
 
   State state_;
   base::TimeTicks close_timestamp_;
 
+  base::RepeatingClosure playback_loop_task_;
   base::flat_map<MixerInput::Source*, std::unique_ptr<MixerInput>> inputs_;
   base::flat_map<MixerInput::Source*, std::unique_ptr<MixerInput>>
       ignored_inputs_;
 
-  base::flat_set<CastMediaShlib::LoopbackAudioObserver*> loopback_observers_;
-
   base::flat_map<AudioContentType, VolumeInfo> volume_info_;
 
   base::flat_map<AudioOutputRedirector*, std::unique_ptr<AudioOutputRedirector>>
@@ -234,8 +219,6 @@ class StreamMixer {
   const bool external_audio_pipeline_supported_;
   std::unique_ptr<BaseExternalMediaVolumeChangeRequestObserver>
       external_volume_observer_;
-  std::unique_ptr<ExternalLoopbackAudioObserver>
-      external_loopback_audio_observer_;
 
   base::WeakPtrFactory<StreamMixer> weak_factory_;
 

chromecast/media/cma/backend/stream_mixer_external_audio_pipeline_unittest.cc

@@ -89,14 +89,9 @@ class ExternalAudioPipelineTest : public ::testing::Test {
   }
   // Run async operations in the stream mixer.
   void RunLoopForMixer() {
-    // SendLoopbackData.
-    base::RunLoop run_loop1;
-    message_loop_->task_runner()->PostTask(FROM_HERE, run_loop1.QuitClosure());
-    run_loop1.Run();
-    // Playbackloop.
-    base::RunLoop run_loop2;
-    message_loop_->task_runner()->PostTask(FROM_HERE, run_loop2.QuitClosure());
-    run_loop2.Run();
+    base::RunLoop run_loop;
+    message_loop_->task_runner()->PostTask(FROM_HERE, run_loop.QuitClosure());
+    run_loop.Run();
   }
 
  protected:
@@ -201,11 +196,10 @@ TEST_F(ExternalAudioPipelineTest, ExternalAudioPipelineLoopbackData) {
   mixer_->AddLoopbackAudioObserver(&mock_loopback_observer);
 
   mixer_->AddInput(&input);
-
   RunLoopForMixer();
+
   // Send data to the stream mixer.
   input.SetData(std::move(data));
-
   RunLoopForMixer();
 
   // Get actual data from our mocked loopback observer.