[Chromoting] Add AudioVolumeApplier to reduce the complexity and the dependency of kChannels

remoting/host/audio_silence_detector.cc

 // 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 "remoting/host/audio_silence_detector.h"
 
 #include <stdlib.h>
 
 namespace remoting {
 
 namespace {
 
 // Silence period threshold in seconds. Silence intervals shorter than this
 // value are still encoded and sent to the client, so that we don't disrupt
 // playback by dropping them.
 int kSilencePeriodThresholdSeconds = 1;
 
 }  // namespace
 
 AudioSilenceDetector::AudioSilenceDetector(int threshold)
     : threshold_(threshold),
       silence_length_max_(0),
-      silence_length_(0) {
+      silence_length_(0),
+      channels_(0) {
   DCHECK_GE(threshold_, 0);
 }
 
 AudioSilenceDetector::~AudioSilenceDetector() {
 }
 
 void AudioSilenceDetector::Reset(int sampling_rate, int channels) {
   DCHECK_GT(sampling_rate, 0);
+  DCHECK_GT(channels, 0);
   silence_length_ = 0;
   silence_length_max_ =
       sampling_rate * channels * kSilencePeriodThresholdSeconds;
+  channels_ = channels;
 }
 
 bool AudioSilenceDetector::IsSilence(const int16_t* samples,
-                                     size_t samples_count) {
+                                     size_t frames) {
+  const int samples_count = frames * channels();
   bool silent_packet = true;
   // Potentially this loop can be optimized (e.g. using SSE or adding special
   // case for threshold_==0), but it's not worth worrying about because the
   // amount of data it processes is relaively small.
-  for (size_t i = 0; i < samples_count; ++i) {
+  for (int i = 0; i < samples_count; ++i) {
     if (abs(samples[i]) > threshold_) {
       silent_packet = false;
       break;
     }
   }
 
   if (!silent_packet) {
     silence_length_ = 0;
     return false;
   }
 
   silence_length_ += samples_count;
   return silence_length_ > silence_length_max_;
 }
 
+int AudioSilenceDetector::channels() const {
+  return channels_;
+}
+
 }  // namespace remoting