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/non_thread_safe.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 base::NonThreadSafe {

[no longer working on chromium, 2014/03/01 11:34:28]

I can't use the NonThreadSafe here since the object will be deleted in the new
capture thread. So I simply add a thread check to make sure Calculate() is
always called on the same thread.

[tommi (sloooow) - chröme, 2014/03/01 11:49:33]

Can you document that then instead?

[no longer working on chromium, 2014/03/01 12:37:00]

Done with adding comment above the thread_check_ member

+ 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:
+  int counter_;
+  int max_amplitude_;
+  int level_;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_MEDIA_MEDIA_STREAM_AUDIO_LEVEL_CALCULATOR_H_