Revert 189095 "Silence detection for audio output UI favicon ind..."

kareng@ noticed crashes.  Must revert before dev channel build.  :(


> Silence detection for audio output UI favicon indicator.
> 
> Added a ProbablyContainsSilence() utility method to media::AudioBus, and then added silence detection logic to media::AudioOutputController.  While the detection logic will run on the "native audio thread," it should use an inconsequential amount of CPU time.  AudioOutputController will invoke a new EventHandler::OnAudible() callback no more often than every 50 ms, and only when transitioning to/from periods of silence.
> 
> Also, to avoid O(N) look-ups in AudioRendererHost for each call to any AudioOutputController::EventHandler method, the interface was simplified such that each stream/controller gets its own EventHandler instance.  Changed AudioRendererHost::AudioEntry to become the class that implements the EventHandler interface.  Lots of related clean-ups throughout audio_renderer_host.cc to deflate the code.
> 
> BUG=178343
> TEST=media_unittests, content_unittests, and confirmation by running chrome manually
> TBR=avi
> 
> 
> Review URL: https://chromiumcodereview.appspot.com/12426002

TBR=miu@chromium.org
Review URL: https://codereview.chromium.org/12927004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@189479 0039d316-1c4b-4281-b951-d872f2087c98

6 files changed, 29 insertions, 542 deletions

diff --git a/media/audio/audio_output_controller.cc b/media/audio/audio_output_controller.cc
index d162cc2..9120706 100644
--- a/media/audio/audio_output_controller.cc
+++ b/media/audio/audio_output_controller.cc
@@ -10,7 +10,6 @@
 #include "base/threading/platform_thread.h"
 #include "base/time.h"
 #include "build/build_config.h"
-#include "media/audio/audio_silence_detector.h"
 #include "media/audio/audio_util.h"
 #include "media/audio/shared_memory_util.h"
 
@@ -19,17 +18,6 @@ using base::TimeDelta;
 
 namespace media {
 
-// Amount of contiguous time where all audio is silent before considering the
-// stream to have transitioned and EventHandler::OnAudible() should be called.
-static const int kQuestionableSilencePeriodMillis = 50;
-
-// Sample value range below which audio is considered indistinguishably silent.
-//
-// TODO(miu): This value should be specified in dbFS units rather than full
-// scale.  See TODO in audio_silence_detector.h.
-static const float kIndistinguishableSilenceThreshold =
-    1.0f / 4096.0f;  // Note: This is approximately -72 dbFS.
-
 // Polling-related constants.
 const int AudioOutputController::kPollNumAttempts = 3;
 const int AudioOutputController::kPollPauseInMilliseconds = 3;
@@ -121,7 +109,7 @@ void AudioOutputController::DoCreate(bool is_for_device_change) {
     state_ = kError;
 
     // TODO(hclam): Define error types.
-    handler_->OnError(0);
+    handler_->OnError(this, 0);
     return;
   }
 
@@ -130,7 +118,7 @@ void AudioOutputController::DoCreate(bool is_for_device_change) {
     state_ = kError;
 
     // TODO(hclam): Define error types.
-    handler_->OnError(0);
+    handler_->OnError(this, 0);
     return;
   }
 
@@ -147,7 +135,7 @@ void AudioOutputController::DoCreate(bool is_for_device_change) {
 
   // And then report we have been created if we haven't done so already.
   if (!is_for_device_change)
-    handler_->OnCreated();
+    handler_->OnCreated(this);
 }
 
 void AudioOutputController::DoPlay() {
@@ -197,20 +185,12 @@ void AudioOutputController::StartStream() {
   DCHECK(message_loop_->BelongsToCurrentThread());
   state_ = kPlaying;
 
-  silence_detector_.reset(new AudioSilenceDetector(
-      params_.sample_rate(),
-      TimeDelta::FromMilliseconds(kQuestionableSilencePeriodMillis),
-      kIndistinguishableSilenceThreshold));
-
   // We start the AudioOutputStream lazily.
   AllowEntryToOnMoreIOData();
   stream_->Start(this);
 
-  // Tell the event handler that we are now playing, and also start the silence
-  // detection notifications.
-  handler_->OnPlaying();
-  silence_detector_->Start(
-      base::Bind(&EventHandler::OnAudible, base::Unretained(handler_)));
+  // Tell the event handler that we are now playing.
+  handler_->OnPlaying(this);
 }
 
 void AudioOutputController::StopStream() {
@@ -223,8 +203,6 @@ void AudioOutputController::StopStream() {
   } else if (state_ == kPlaying) {
     stream_->Stop();
     DisallowEntryToOnMoreIOData();
-    silence_detector_->Stop(true);
-    silence_detector_.reset();
     state_ = kPaused;
   }
 }
@@ -240,7 +218,7 @@ void AudioOutputController::DoPause() {
   // Send a special pause mark to the low-latency audio thread.
   sync_reader_->UpdatePendingBytes(kPauseMark);
 
-  handler_->OnPaused();
+  handler_->OnPaused(this);
 }
 
 void AudioOutputController::DoFlush() {
@@ -281,7 +259,7 @@ void AudioOutputController::DoSetVolume(double volume) {
 void AudioOutputController::DoReportError(int code) {
   DCHECK(message_loop_->BelongsToCurrentThread());
   if (state_ != kClosed)
-    handler_->OnError(code);
+    handler_->OnError(this, code);
 }
 
 int AudioOutputController::OnMoreData(AudioBus* dest,
@@ -310,8 +288,6 @@ int AudioOutputController::OnMoreIOData(AudioBus* source,
   sync_reader_->UpdatePendingBytes(
       buffers_state.total_bytes() + frames * params_.GetBytesPerFrame());
 
-  silence_detector_->Scan(dest, frames);
-
   AllowEntryToOnMoreIOData();
   return frames;
 }
diff --git a/media/audio/audio_output_controller.h b/media/audio/audio_output_controller.h
index cfb685f..e8fae22 100644
--- a/media/audio/audio_output_controller.h
+++ b/media/audio/audio_output_controller.h
@@ -8,9 +8,7 @@
 #include "base/atomic_ref_count.h"
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
-#include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
-#include "base/timer.h"
 #include "media/audio/audio_buffers_state.h"
 #include "media/audio/audio_io.h"
 #include "media/audio/audio_manager.h"
@@ -59,8 +57,6 @@ class MessageLoop;
 
 namespace media {
 
-class AudioSilenceDetector;
-
 class MEDIA_EXPORT AudioOutputController
     : public base::RefCountedThreadSafe<AudioOutputController>,
       public AudioOutputStream::AudioSourceCallback,
@@ -71,12 +67,12 @@ class MEDIA_EXPORT AudioOutputController
   // following methods are called on the audio manager thread.
   class MEDIA_EXPORT EventHandler {
    public:
-    virtual void OnCreated() = 0;
-    virtual void OnPlaying() = 0;
-    virtual void OnAudible(bool is_audible) = 0;
-    virtual void OnPaused() = 0;
-    virtual void OnError(int error_code) = 0;
-    virtual void OnDeviceChange(int new_buffer_size, int new_sample_rate) = 0;
+    virtual void OnCreated(AudioOutputController* controller) = 0;
+    virtual void OnPlaying(AudioOutputController* controller) = 0;
+    virtual void OnPaused(AudioOutputController* controller) = 0;
+    virtual void OnError(AudioOutputController* controller, int error_code) = 0;
+    virtual void OnDeviceChange(AudioOutputController* controller,
+                                int new_buffer_size, int new_sample_rate) = 0;
 
    protected:
     virtual ~EventHandler() {}
@@ -197,10 +193,6 @@ class MEDIA_EXPORT AudioOutputController
   void DoStartDiverting(AudioOutputStream* to_stream);
   void DoStopDiverting();
 
-  // Called at regular intervals during playback to check for a change in
-  // silence and call EventHandler::OnAudible() when state changes occur.
-  void MaybeInvokeAudibleCallback();
-
   // Helper methods that start/stop physical stream.
   void StartStream();
   void StopStream();
@@ -253,11 +245,6 @@ class MEDIA_EXPORT AudioOutputController
   // (when starting-up a stream).
   base::WeakPtrFactory<AudioOutputController> weak_this_;
 
-  // Scans audio samples from OnMoreIOData() as input and causes
-  // EventHandler::OnAudbile() to be called whenever a transition to a period of
-  // silence or non-silence is detected.
-  scoped_ptr<AudioSilenceDetector> silence_detector_;
-
   DISALLOW_COPY_AND_ASSIGN(AudioOutputController);
 };
 
diff --git a/media/audio/audio_output_controller_unittest.cc b/media/audio/audio_output_controller_unittest.cc
index 699810f..944d661 100644
--- a/media/audio/audio_output_controller_unittest.cc
+++ b/media/audio/audio_output_controller_unittest.cc
@@ -38,13 +38,13 @@ class MockAudioOutputControllerEventHandler
  public:
   MockAudioOutputControllerEventHandler() {}
 
-  MOCK_METHOD0(OnCreated, void());
-  MOCK_METHOD0(OnPlaying, void());
-  MOCK_METHOD1(OnAudible, void(bool is_audible));
-  MOCK_METHOD0(OnPaused, void());
-  MOCK_METHOD1(OnError, void(int error_code));
-  MOCK_METHOD2(OnDeviceChange, void(int new_buffer_size, int new_sample_rate));
-
+  MOCK_METHOD1(OnCreated, void(AudioOutputController* controller));
+  MOCK_METHOD1(OnPlaying, void(AudioOutputController* controller));
+  MOCK_METHOD1(OnPaused, void(AudioOutputController* controller));
+  MOCK_METHOD2(OnError, void(AudioOutputController* controller,
+                             int error_code));
+  MOCK_METHOD3(OnDeviceChange, void(AudioOutputController* controller,
+                                    int new_buffer_size, int new_sample_rate));
  private:
   DISALLOW_COPY_AND_ASSIGN(MockAudioOutputControllerEventHandler);
 };
@@ -117,7 +117,7 @@ class AudioOutputControllerTest : public testing::Test {
         kSampleRate, kBitsPerSample, samples_per_packet);
 
     if (params_.IsValid()) {
-      EXPECT_CALL(mock_event_handler_, OnCreated())
+      EXPECT_CALL(mock_event_handler_, OnCreated(NotNull()))
           .WillOnce(SignalEvent(&create_event_));
     }
 
@@ -131,17 +131,14 @@ class AudioOutputControllerTest : public testing::Test {
   }
 
   void Play() {
-    // Expect the event handler to receive one OnPlaying() call and one or more
-    // OnAudible() calls.
-    EXPECT_CALL(mock_event_handler_, OnPlaying())
+    // Expect the event handler to receive one OnPlaying() call.
+    EXPECT_CALL(mock_event_handler_, OnPlaying(NotNull()))
         .WillOnce(SignalEvent(&play_event_));
-    EXPECT_CALL(mock_event_handler_, OnAudible(_))
-        .Times(AtLeast(1));
 
     // During playback, the mock pretends to provide audio data rendered and
     // sent from the render process.
     EXPECT_CALL(mock_sync_reader_, UpdatePendingBytes(_))
-        .Times(AtLeast(1));
+        .Times(AtLeast(2));
     EXPECT_CALL(mock_sync_reader_, Read(_, _))
         .WillRepeatedly(DoAll(PopulateBuffer(),
                               SignalEvent(&read_event_),
@@ -154,7 +151,7 @@ class AudioOutputControllerTest : public testing::Test {
 
   void Pause() {
     // Expect the event handler to receive one OnPaused() call.
-    EXPECT_CALL(mock_event_handler_, OnPaused())
+    EXPECT_CALL(mock_event_handler_, OnPaused(NotNull()))
         .WillOnce(SignalEvent(&pause_event_));
 
     controller_->Pause();
@@ -163,9 +160,9 @@ class AudioOutputControllerTest : public testing::Test {
   void ChangeDevice() {
     // Expect the event handler to receive one OnPaying() call and no OnPaused()
     // call.
-    EXPECT_CALL(mock_event_handler_, OnPlaying())
+    EXPECT_CALL(mock_event_handler_, OnPlaying(NotNull()))
         .WillOnce(SignalEvent(&play_event_));
-    EXPECT_CALL(mock_event_handler_, OnPaused())
+    EXPECT_CALL(mock_event_handler_, OnPaused(NotNull()))
         .Times(0);
 
     // Simulate a device change event to AudioOutputController from the
@@ -179,7 +176,7 @@ class AudioOutputControllerTest : public testing::Test {
     if (was_playing) {
       // Expect the handler to receive one OnPlaying() call as a result of the
       // stream switching.
-      EXPECT_CALL(mock_event_handler_, OnPlaying())
+      EXPECT_CALL(mock_event_handler_, OnPlaying(NotNull()))
           .WillOnce(SignalEvent(&play_event_));
     }
 
@@ -211,7 +208,7 @@ class AudioOutputControllerTest : public testing::Test {
     if (was_playing) {
       // Expect the handler to receive one OnPlaying() call as a result of the
       // stream switching back.
-      EXPECT_CALL(mock_event_handler_, OnPlaying())
+      EXPECT_CALL(mock_event_handler_, OnPlaying(NotNull()))
           .WillOnce(SignalEvent(&play_event_));
     }
 
diff --git a/media/audio/audio_silence_detector.cc b/media/audio/audio_silence_detector.cc
deleted file mode 100644
index 4f4bc06..0000000
--- a/media/audio/audio_silence_detector.cc
+++ /dev/null
@@ -1,134 +0,0 @@
-// Copyright (c) 2013 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/audio_silence_detector.h"
-
-#include "base/float_util.h"
-#include "base/time.h"
-#include "media/base/audio_bus.h"
-
-using base::AtomicRefCountDec;
-using base::AtomicRefCountInc;
-using base::AtomicRefCountIsOne;
-using base::AtomicRefCountIsZero;
-
-namespace media {
-
-AudioSilenceDetector::AudioSilenceDetector(
-    int sample_rate,
-    const base::TimeDelta& questionable_silence_period,
-    float indistinguishable_silence_threshold)
-    : polling_period_(questionable_silence_period),
-      frames_before_observing_silence_(
-          sample_rate * questionable_silence_period.InSecondsF()),
-      silence_threshold_(indistinguishable_silence_threshold),
-      frames_silent_so_far_(frames_before_observing_silence_),
-      observing_silence_(1),
-      was_audible_(false) {
-}
-
-AudioSilenceDetector::~AudioSilenceDetector() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  // Note: If active, ~RepeatingTimer() will StopAndAbandon().
-}
-
-void AudioSilenceDetector::Start(const AudibleCallback& callback) {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  DCHECK(notify_is_audible_.is_null());
-  DCHECK(!callback.is_null());
-
-  notify_is_audible_ = callback;
-  was_audible_ = AtomicRefCountIsZero(&observing_silence_);
-  notify_is_audible_.Run(was_audible_);
-  poll_timer_.Start(
-      FROM_HERE, polling_period_,
-      this, &AudioSilenceDetector::MaybeInvokeAudibleCallback);
-}
-
-void AudioSilenceDetector::Stop(bool notify_ending_in_silence) {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  DCHECK(!notify_is_audible_.is_null());
-
-  poll_timer_.Stop();
-  if (notify_ending_in_silence)
-    notify_is_audible_.Run(false);
-  notify_is_audible_.Reset();
-}
-
-void AudioSilenceDetector::Scan(const AudioBus* buffer, int frames) {
-  // Determine whether the frames just read are probably silence.  If enough
-  // frames of silence have been observed, flip the |observing_silence_|
-  // boolean, which will be read by another thread.
-  if (ProbablyContainsSilence(buffer, frames)) {
-    // Note: Prevent indefinite incrementing of |frames_silent_so_far_|, to
-    // avoid eventual integer overflow.
-    if (frames_silent_so_far_ < frames_before_observing_silence_) {
-      frames_silent_so_far_ += frames;
-      if (frames_silent_so_far_ >= frames_before_observing_silence_) {
-        DCHECK(AtomicRefCountIsZero(&observing_silence_));
-        AtomicRefCountInc(&observing_silence_);
-      }
-    }
-  } else {
-    if (frames_silent_so_far_ >= frames_before_observing_silence_) {
-      DCHECK(AtomicRefCountIsOne(&observing_silence_));
-      AtomicRefCountDec(&observing_silence_);
-    }
-    frames_silent_so_far_ = 0;
-  }
-}
-
-void AudioSilenceDetector::MaybeInvokeAudibleCallback() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-
-  const bool is_now_audible = AtomicRefCountIsZero(&observing_silence_);
-  if (was_audible_ && !is_now_audible)
-    notify_is_audible_.Run(was_audible_ = false);
-  else if (!was_audible_ && is_now_audible)
-    notify_is_audible_.Run(was_audible_ = true);
-}
-
-bool AudioSilenceDetector::ProbablyContainsSilence(const AudioBus* buffer,
-                                                   int num_frames) {
-  if (!buffer)
-    return true;
-  DCHECK_LE(num_frames, buffer->frames());
-  if (buffer->frames() <= 0)
-    return true;
-
-  // Scan the data in each channel.  If any one channel contains sound whose
-  // range of values exceeds |silence_threshold_|, return false immediately.
-  for (int i = 0; i < buffer->channels(); ++i) {
-    // Examine the 1st, 2nd (+1), 4th (+2), 7th (+3), 11th (+4), etc. samples,
-    // checking whether |silence_threshold_| has been breached each time.  For
-    // typical AudioBus sizes, this algorithm will in the worst case examine
-    // fewer than 10% of the samples.
-    //
-    // Note that there *is* a heavy bias in sampling at the beginning of the
-    // channels, but that doesn't matter.  The buffer sizes are simply too
-    // small.  For example, it is commonplace to use 128-sample buffers, which
-    // represents ~3 ms of audio at 44.1 kHz; and this means that frequencies
-    // below ~350 Hz will span more than one buffer to make a full cycle.  In
-    // all, the algorithm here is meant to be dirt-simple math that isn't
-    // susceptible to periodic bias within a single buffer.
-    const float* p = buffer->channel(i);
-    const float* const end_of_samples = p + num_frames;
-    int skip = 1;
-    float min_value = *p;
-    float max_value = *p;
-    for (p += skip; p < end_of_samples; ++skip, p += skip) {
-      DCHECK(base::IsFinite(*p));
-      if (*p < min_value)
-        min_value = *p;
-      else if (max_value < *p)
-        max_value = *p;
-      if ((max_value - min_value) > silence_threshold_)
-        return false;
-    }
-  }
-
-  return true;
-}
-
-}  // namespace media
diff --git a/media/audio/audio_silence_detector.h b/media/audio/audio_silence_detector.h
deleted file mode 100644
index b6c52a7..0000000
--- a/media/audio/audio_silence_detector.h
+++ /dev/null
@@ -1,112 +0,0 @@
-// Copyright (c) 2013 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 MEDIA_AUDIO_AUDIO_SILENCE_DETECTOR_H_
-#define MEDIA_AUDIO_AUDIO_SILENCE_DETECTOR_H_
-
-#include "base/atomic_ref_count.h"
-#include "base/callback.h"
-#include "base/memory/scoped_ptr.h"
-#include "base/threading/thread_checker.h"
-#include "base/timer.h"
-#include "media/base/media_export.h"
-
-// An audio silence detector.  It is periodically provided an AudioBus by the
-// native audio thread, where simple logic determines whether the audio samples
-// in each channel in the buffer represent silence.  If a long-enough period of
-// contiguous silence is observed in all channels, a notification callback is
-// run on the thread that constructed AudioSilenceDetector.
-//
-// Note that extreme care has been taken to make the
-// AudioSilenceDetector::Scan() method safe to be called on the native audio
-// thread.  The code acquires no locks, nor engages in any operation that could
-// result in an undetermined/unbounded amount of run-time.  Comments in
-// audio_silence_detector.cc elaborate further on the silence detection
-// algorithm.
-
-namespace base {
-class TimeDelta;
-}
-
-namespace media {
-
-class AudioBus;
-
-class MEDIA_EXPORT AudioSilenceDetector {
- public:
-  typedef base::Callback<void(bool)> AudibleCallback;
-
-  // Tunable parameters: |questionable_silence_period| is the amount of time
-  // where audio must remain silent before triggerring a callback.
-  // |indistinguishable_silence_threshold| is the value range below which audio
-  // is considered silent, in full-scale units.
-  //
-  // TODO(miu): |indistinguishable_silence_threshold| should be specified in
-  // dbFS units rather than full-scale.  We need a dbFS data type for
-  // media/audio first.
-  AudioSilenceDetector(int sample_rate,
-                       const base::TimeDelta& questionable_silence_period,
-                       float indistinguishable_silence_threshold);
-
-  ~AudioSilenceDetector();
-
-  // Start detecting silence, notifying via the given callback.
-  void Start(const AudibleCallback& notify_is_audible);
-
-  // Stop detecting silence.  If |notify_ending_in_silence| is true, a final
-  // notify_is_audible(false) call will be made here.
-  void Stop(bool notify_ending_in_silence);
-
-  // Scan more |frames| of audio data from |buffer|.  This is usually called
-  // within the native audio thread's "more data" callback.
-  void Scan(const AudioBus* buffer, int frames);
-
- private:
-  // Called by |poll_timer_| at regular intervals to determine whether to invoke
-  // the callback due to a silence state change.
-  void MaybeInvokeAudibleCallback();
-
-  // Returns true if the first |num_frames| frames in all channels in |buffer|
-  // probably contain silence.  A simple heuristic is used to quickly examine a
-  // subset of the samples in each channel, hence the name of this method.
-  // "Silence" means that the range of the sample values examined does not
-  // exceed |silence_threshold_|.
-  bool ProbablyContainsSilence(const AudioBus* buffer, int num_frames);
-
-  // Time between polls for changes in state.
-  const base::TimeDelta polling_period_;
-
-  // Number of frames of contiguous silence to be observed before setting
-  // |observing_silence_| to false.
-  const int frames_before_observing_silence_;
-
-  // Threshold below which audio should be considered indistinguishably silent.
-  const float silence_threshold_;
-
-  // Number of frames of contiguous silence observed thus far on the native
-  // audio thread.
-  int frames_silent_so_far_;
-
-  // Boolean state (0 or 1) set by the native audio thread.  This is polled
-  // regularly by the thread that invokes the callback.
-  base::AtomicRefCount observing_silence_;
-
-  // Callback for notifying of a detected transition to silence or non-silence.
-  AudibleCallback notify_is_audible_;
-
-  // Last reported audible state, used for de-duping callback invocations.
-  bool was_audible_;
-
-  // Fires regularly, calling MaybeInvokeAudibleCallback().
-  base::RepeatingTimer<AudioSilenceDetector> poll_timer_;
-
-  // Constructor, destructor and most methods must be called on the same thread.
-  base::ThreadChecker thread_checker_;
-
-  DISALLOW_COPY_AND_ASSIGN(AudioSilenceDetector);
-};
-
-}  // namespace media
-
-#endif  // MEDIA_AUDIO_AUDIO_SILENCE_DETECTOR_H_
diff --git a/media/audio/audio_silence_detector_unittest.cc b/media/audio/audio_silence_detector_unittest.cc
deleted file mode 100644
index 52e6958..0000000
--- a/media/audio/audio_silence_detector_unittest.cc
+++ /dev/null
@@ -1,227 +0,0 @@
-// Copyright (c) 2013 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/audio_silence_detector.h"
-
-#include "base/bind.h"
-#include "base/bind_helpers.h"
-#include "base/message_loop.h"
-#include "base/synchronization/waitable_event.h"
-#include "base/threading/thread.h"
-#include "base/time.h"
-#include "media/base/audio_bus.h"
-#include "testing/gmock/include/gmock/gmock.h"
-#include "testing/gtest/include/gtest/gtest.h"
-
-using ::testing::_;
-using ::testing::InvokeWithoutArgs;
-using ::testing::TestWithParam;
-using ::testing::Values;
-
-namespace media {
-
-static const int kSampleRate = 48000;
-static const int kFramesPerBuffer = 128;
-
-namespace {
-
-class MockObserver {
- public:
-  MOCK_METHOD1(OnAudible, void(bool));
-};
-
-struct TestScenario {
-  const float* data;
-  int num_channels;
-  int num_frames;
-  float value_range;
-
-  TestScenario(const float* d, int c, int f, float v)
-      : data(d), num_channels(c), num_frames(f), value_range(v) {}
-};
-
-}  // namespace
-
-class AudioSilenceDetectorTest : public TestWithParam<TestScenario> {
- public:
-  AudioSilenceDetectorTest()
-      : audio_manager_thread_(new base::Thread("AudioThread")),
-        notification_received_(false, false) {
-    audio_manager_thread_->Start();
-    audio_message_loop_ = audio_manager_thread_->message_loop_proxy();
-  }
-
-  virtual ~AudioSilenceDetectorTest() {
-    SyncWithAudioThread();
-  }
-
-  AudioSilenceDetector* silence_detector() const {
-    return silence_detector_.get();
-  }
-
-  void StartSilenceDetector(float threshold, MockObserver* observer) {
-    audio_message_loop_->PostTask(
-        FROM_HERE,
-        base::Bind(&AudioSilenceDetectorTest::StartDetectorOnAudioThread,
-                   base::Unretained(this), threshold, observer));
-    SyncWithAudioThread();
-  }
-
-  void StopSilenceDetector() {
-    audio_message_loop_->PostTask(
-        FROM_HERE,
-        base::Bind(&AudioSilenceDetectorTest::StopDetectorOnAudioThread,
-                   base::Unretained(this)));
-    SyncWithAudioThread();
-  }
-
-  // Creates an AudioBus, sized and populated with kFramesPerBuffer frames of
-  // data.  The given test |data| is repeated to fill the buffer.
-  scoped_ptr<AudioBus> CreatePopulatedBuffer(
-      const float* data, int num_channels, int num_frames) {
-    scoped_ptr<AudioBus> bus = AudioBus::Create(num_channels, kFramesPerBuffer);
-    for (int ch = 0; ch < num_channels; ++ch) {
-      for (int frames = 0; frames < kFramesPerBuffer; frames += num_frames) {
-        const int num_to_copy = std::min(num_frames, kFramesPerBuffer - frames);
-        memcpy(bus->channel(ch) + frames, data + num_frames * ch,
-               sizeof(float) * num_to_copy);
-      }
-    }
-    return bus.Pass();
-  }
-
-  void SignalNotificationReceived() {
-    notification_received_.Signal();
-  }
-
-  void WaitForNotificationReceived() {
-    notification_received_.Wait();
-  }
-
-  // Post a task on the audio thread and block until it is executed.  This
-  // provides a barrier: All previous tasks pending on the audio thread have
-  // completed before this method returns.
-  void SyncWithAudioThread() {
-    base::WaitableEvent done(false, false);
-    audio_message_loop_->PostTask(
-        FROM_HERE,
-        base::Bind(&base::WaitableEvent::Signal, base::Unretained(&done)));
-    done.Wait();
-  }
-
- private:
-  void StartDetectorOnAudioThread(float threshold, MockObserver* observer) {
-    const AudioSilenceDetector::AudibleCallback notify_is_audible =
-        base::Bind(&MockObserver::OnAudible, base::Unretained(observer));
-    silence_detector_.reset(new AudioSilenceDetector(
-        kSampleRate, base::TimeDelta::FromMilliseconds(1), threshold));
-    silence_detector_->Start(notify_is_audible);
-  }
-
-  void StopDetectorOnAudioThread() {
-    silence_detector_->Stop(true);
-    silence_detector_.reset();
-  }
-
-  scoped_ptr<base::Thread> audio_manager_thread_;
-  scoped_refptr<base::MessageLoopProxy> audio_message_loop_;
-
-  base::WaitableEvent notification_received_;
-
-  scoped_ptr<AudioSilenceDetector> silence_detector_;
-
-  DISALLOW_COPY_AND_ASSIGN(AudioSilenceDetectorTest);
-};
-
-TEST_P(AudioSilenceDetectorTest, TriggersAtVariousThresholds) {
-  static const float kThresholdsToTry[] =
-      { 0.0f, 0.125f, 0.25f, 0.5f, 0.75f, 1.0f };
-
-  const TestScenario& scenario = GetParam();
-
-  for (size_t i = 0; i < arraysize(kThresholdsToTry); ++i) {
-    MockObserver observer;
-
-    // Start the detector.  This should cause a single callback to indicate
-    // we're starting out in silence.
-    EXPECT_CALL(observer, OnAudible(false))
-        .WillOnce(InvokeWithoutArgs(
-            this, &AudioSilenceDetectorTest::SignalNotificationReceived))
-        .RetiresOnSaturation();
-    StartSilenceDetector(kThresholdsToTry[i], &observer);
-    WaitForNotificationReceived();
-
-    // Send more data to the silence detector.  For some test scenarios, the
-    // sound data will trigger a callback.
-    const bool expect_a_callback = (kThresholdsToTry[i] < scenario.value_range);
-    if (expect_a_callback) {
-      EXPECT_CALL(observer, OnAudible(true))
-          .WillOnce(InvokeWithoutArgs(
-              this, &AudioSilenceDetectorTest::SignalNotificationReceived))
-          .RetiresOnSaturation();
-    }
-    scoped_ptr<AudioBus> bus = CreatePopulatedBuffer(
-        scenario.data, scenario.num_channels, scenario.num_frames);
-    silence_detector()->Scan(bus.get(), bus->frames());
-    if (expect_a_callback)
-      WaitForNotificationReceived();
-
-    // Stop the detector.  This should cause another callback to indicate we're
-    // ending in silence.
-    EXPECT_CALL(observer, OnAudible(false))
-        .WillOnce(InvokeWithoutArgs(
-            this, &AudioSilenceDetectorTest::SignalNotificationReceived))
-        .RetiresOnSaturation();
-    StopSilenceDetector();
-    WaitForNotificationReceived();
-
-    SyncWithAudioThread();
-  }
-}
-
-static const float kAllZeros[] = {
-  // left channel
-  0.0f,
-  // right channel
-  0.0f
-};
-
-static const float kAllOnes[] = {
-  // left channel
-  1.0f,
-  // right channel
-  1.0f
-};
-
-static const float kSilentLeftChannel[] = {
-  // left channel
-  0.5f, 0.5f, 0.5f, 0.5f,
-  // right channel
-  0.0f, 0.25f, 0.0f, 0.0f
-};
-
-static const float kSilentRightChannel[] = {
-  // left channel
-  1.0f, 1.0f, 0.75f, 0.5f, 1.0f,
-  // right channel
-  0.0f, 0.0f, 0.0f, 0.0f, 0.0f
-};
-
-static const float kAtDifferentVolumesAndBias[] = {
-  // left channel
-  1.0f, 0.9f, 0.8f, 0.7f, 0.6f, 0.5f, 0.4f, 0.5f, 0.6f, 0.7f, 0.8f, 0.9f,
-  // right channel
-  0.0f, 0.2f, 0.4f, 0.6f, 0.4f, 0.2f, 0.0f, 0.2f, 0.4f, 0.6f, 0.4f, 0.2f
-};
-
-INSTANTIATE_TEST_CASE_P(
-    Scenarios, AudioSilenceDetectorTest,
-    Values(
-        TestScenario(kAllZeros, 2, 1, 0.0f),
-        TestScenario(kAllOnes, 2, 1, 0.0f),
-        TestScenario(kSilentLeftChannel, 2, 4, 0.25f),
-        TestScenario(kSilentRightChannel, 2, 5, 0.5f),
-        TestScenario(kAtDifferentVolumesAndBias, 2, 12, 0.6f)));
-
-}  // namespace media