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 {
+ 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,

[tommi (sloooow) - chröme, 2014/02/27 08:39:43]

would it make sense to add another Calculate method that accepts an AudioBus
instead of these parameters and have a TODO to remove this one?  That way, we
can use that method straight away whenever we have an AudioBus instance (e.g.
while behind the flag) and we don't have to go and update that code once we get
rid of the int16 assumption.

[no longer working on chromium, 2014/02/28 08:16:25]

We may have to keep using const int16* until we can completely remove the flag.
That is because adding a callback using AudioBus* will touch all the code from
source, track, then down to the sinks. We (WebRtc) can live with it, but the
sink clients probably don't want a un-used overload method.

My plan was to switch const int16* to AudioBus* when we are removing the flag,
and do the change in all the layers at the same time. But I am fine with adding
a Calculate(AudioBus*) here if you strongly want it.

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