Replace AudioSilenceDetector with an AudioPowerMonitor.

media/audio/audio_silence_detector.h

-// 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/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_