Replace AudioSilenceDetector with an AudioPowerMonitor.

media/audio/audio_silence_detector.cc

Index: media/audio/audio_silence_detector.cc
diff --git a/media/audio/audio_silence_detector.cc b/media/audio/audio_silence_detector.cc
deleted file mode 100644
index a37faef5f453003217088810feddcd8360056b18..0000000000000000000000000000000000000000
--- 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/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