Calculate the signal level on the media stream local audio track

content/renderer/media/media_stream_audio_level_calculator.h

+// Copyright 2014 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 CONTENT_RENDERER_MEDIA_MEDIA_STREAM_AUDIO_LEVEL_CALCULATOR_H_
+#define CONTENT_RENDERER_MEDIA_MEDIA_STREAM_AUDIO_LEVEL_CALCULATOR_H_
+
+#include "base/threading/thread_checker.h"
+
+namespace content {
+
+// This class is used by the WebRtcLocalAudioTrack to calculate the  level of
+// the audio signal. And the audio level will be eventually used by the volume
+// animation UI.
+// The algorithm used by this class is the same as how it is done in
+// third_party/webrtc/voice_engine/level_indicator.cc.
+class MediaStreamAudioLevelCalculator {
+ public:
+  MediaStreamAudioLevelCalculator();
+  ~MediaStreamAudioLevelCalculator();
+
+  // Calculates the signal level of the audio data.
+  // Returns the level of bars that the volume animation UI uses for
+  // presenting the energy level of the audio data.
+  int Calculate(const int16* audio_data, int number_of_channels,
+                int number_of_frames);
+
+ private:
+  // Used to DCHECK that the constructor and Calculate() are always called on
+  // the same audio thread. Note that the destructor will be called on a
+  // different thread, which can be either the main render thread or a new
+  // audio thread where WebRtcLocalAudioTrack::OnSetFormat() is called.
+  base::ThreadChecker thread_checker_;
+
+  int counter_;
+  int max_amplitude_;
+  int level_;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_MEDIA_MEDIA_STREAM_AUDIO_LEVEL_CALCULATOR_H_