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

remoting/host/audio_volume_applier.cc

+// Copyright 2017 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_volume_applier.h"
+
+namespace remoting {
+
+AudioVolumeApplier::AudioVolumeApplier(int silence_threshold)
+    : silence_detector_before_(silence_threshold),
+      silence_detector_after_(silence_threshold) {}

[Sergey Ulanov, 2017/04/26 19:57:35]

I don't think we need the post-processing silence detection. It's not likely to
be useful in many cases, but it makes this code more complicated. I think it's
better to apply silence detection on the input only and mute the stream when
volume = 0. 

[Hzj_jie, 2017/04/28 03:53:34]

Done.

+AudioVolumeApplier::~AudioVolumeApplier() = default;
+
+bool AudioVolumeApplier::Apply(int16_t* data, size_t frames) {
+  if (frames == 0) {
+    return false;
+  }
+
+  bool result = ApplyVolumeLevel(data, frames);
+  return !silence_detector_after_.IsSilence(data, frames) && result;
+}
+
+void AudioVolumeApplier::Initialize(int sampling_rate, int channels) {
+  silence_detector_before_.Reset(sampling_rate, channels);
+  silence_detector_after_.Reset(sampling_rate, channels);
+}
+
+bool AudioVolumeApplier::ApplyVolumeLevel(int16_t* data, size_t frames) {
+  if (silence_detector_before_.IsSilence(data, frames)) {
+    return false;
+  }
+
+  float level = GetAudioLevel();
+  if (level == 0) {
+    return false;
+  }
+
+  if (level == 1) {
+    return true;
+  }
+
+  const int sample_count = frames * silence_detector_before_.channels();
+  const int32_t level_int = static_cast<int32_t>(level * 65536);
+  for (int i = 0; i < sample_count; i++) {
+    data[i] = (static_cast<int32_t>(data[i]) * level_int) >> 16;
+  }
+
+  return true;
+}
+
+}  // namespace remoting