Add detection for repeated audio in capturing.

content/renderer/media/repetition_detector.h

Index: content/renderer/media/repetition_detector.h
diff --git a/content/renderer/media/repetition_detector.h b/content/renderer/media/repetition_detector.h
new file mode 100644
index 0000000000000000000000000000000000000000..2b65011cab02559266b10f6e63e7b0cb03bdc652
--- /dev/null
+++ b/content/renderer/media/repetition_detector.h
@@ -0,0 +1,101 @@
+// Copyright 2015 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_REPETITION_DETECTOR_H_
+#define CONTENT_RENDERER_MEDIA_REPETITION_DETECTOR_H_
+
+#include <vector>
+
+#include "base/memory/scoped_vector.h"
+#include "content/common/content_export.h"
+
+namespace content {
+
+class RepetitionDetectorForTest;

[Henrik Grunell, 2015/09/23 10:36:42]

Remove.

[minyue, 2015/09/25 14:40:08]

Done.

+
+class CONTENT_EXPORT RepetitionDetector {

[Henrik Grunell, 2015/09/23 10:36:42]

Call it AudioRepetitionDetector. (And rename files etc.)

[Henrik Grunell, 2015/09/23 10:36:42]

Add comment describing the class briefly. Also give an overview of the detection
algorithm.

[minyue, 2015/09/25 14:40:08]

Done.

[minyue, 2015/09/25 14:40:08]

Done.

+ public:
+  RepetitionDetector();
+  virtual ~RepetitionDetector();

[tommi (sloooow) - chröme, 2015/09/25 08:57:14]

Can you add documentation for the class, what it does, why we have it etc. Would
also be good to document why there are virtual methods.

[minyue, 2015/09/25 14:40:08]

Yes, also per Henrik's request. The virtual is because we have another virtual
function, I don't know if this needs any additional comment.

+
+  struct Pattern {

[Henrik Grunell, 2015/09/23 10:36:42]

Can this be private?

[minyue, 2015/09/25 14:40:08]

Not really if we want the RegisterRepetitionPatterns to take outside (like
global) variable.

+    int id_;
+    // All followings are in milliseconds, since repetition patterns are

[Henrik Grunell, 2015/09/23 10:36:42]

Move this comment to before the struct statement, and expand it to be a general
comment about the struct. What is is used for?

[minyue, 2015/09/25 14:40:08]

Done.

+    // supposedly bounded to certain duration in time.
+    int look_back_ms_;
+    int min_length_ms_;
+  };
+
+  // Detect repetition in |data|. When multichannel, samples should be
+  // interleaved.

[Henrik Grunell, 2015/09/23 10:36:42]

Describe what it does if repetition is detected.

[minyue, 2015/09/25 14:40:08]

Done.

+  void Detect(const float* data, size_t num_frames, size_t num_channels,

[Henrik Grunell, 2015/09/23 10:36:42]

This should take a const AudioBus*.

[minyue, 2015/09/25 14:40:08]

See my comment on a concern of making input format generic.

+              int sample_rate_hz);
+
+ private:
+  friend class RepetitionDetectorForTest;  // For testing.

[Henrik Grunell, 2015/09/23 10:36:42]

Should you use FRIEND_TEST_ALL_PREFIXES()? See other tests.

[minyue, 2015/09/25 14:40:08]

This has been considered and discussed in the parallel CL. The complication is

RepetitionDetectorForTest is not Test, but an inherit of RepetitionDetector.
RepetitionDetectorTest is the actually test. 

FRIEND_TEST is used upon gTests, such as RepetitionDetectorTest, but it is
RepetitionDetectorForTest that needs to access private members.

[tommi (sloooow) - chröme, 2015/09/28 10:28:39]

Did you discuss making the parts that the derived class needs access to,
protected instead?

[minyue, 2015/09/28 14:47:50]

I used protected, and reviewers wanted me to use Friend instead.

+
+  class State {

[Henrik Grunell, 2015/09/23 10:36:42]

Comment and describe the class and what it's used for. Also, the functions in it
need to be described.

[minyue, 2015/09/25 14:40:08]

Done.

+   public:
+    State(int id, int look_back_ms, int min_length_ms);
+
+    bool reported() const { return reported_; }
+    void set_reported(bool reported) { reported_ = reported; }
+
+    // Increase the counter by 1, and tell if the counted audio is zero.
+    void Increment(bool zero);
+
+    bool HasValidReport(int sample_rate_khz) const;
+
+    void Reset();
+    int id() const { return id_; }
+    int look_back_ms() const { return look_back_ms_; }
+
+   private:
+    const int id_;

[Henrik Grunell, 2015/09/23 10:36:42]

Comment on all member variables.

[minyue, 2015/09/25 14:40:08]

Done.

+    const int look_back_ms_;
+    const int min_length_ms_;
+    size_t count_frames_;
+    bool all_zero_;
+    bool reported_;
+  };
+
+  void RegisterRepetitionPatterns(const Pattern* patterns,
+                                  size_t num_patterns);
+
+  void ClearRepetitionPatterns();
+
+  // Reset |audio_buffer_| when number of channels or sample rate changes.
+  void Reset(size_t num_channels, int sample_rate_hz);
+
+  // Add frames (interleaved if stereo) to |audio_buffer_|.
+  void AddFramesToBuffer(const float* data, size_t num_frames);
+
+  // Determine if an audio frame (samples interleaved if stereo) is identical to
+  // |audio_buffer_| at a look back position.
+  bool Equal(const float* frame, int look_back_samples) const;
+
+  // Determine if an audio frame (samples interleaved if stereo) is zero.
+  bool IsZero(const float* frame) const;
+
+  // Action when found repetition.
+  virtual void ReportRepetition(int id);
+
+  std::vector<int> ids_;

[Henrik Grunell, 2015/09/23 10:36:42]

Comment on all member variables.

[minyue, 2015/09/25 14:40:08]

Done.

+  ScopedVector<State> states_;
+  int max_look_back_ms_;
+
+  std::vector<float> audio_buffer_;  // Ring buffers to store input audio.

[Henrik Grunell, 2015/09/23 10:36:42]

Put comments on its own line before the variable.

[minyue, 2015/09/25 14:40:08]

Done.

+  size_t num_channels_;  // Number of audio channels in buffer.
+  int sample_rate_hz_;  // Sample rate in Hz.
+  size_t buffer_size_frames_;  // Number of frames in |audio_buffer|.
+  size_t buffer_end_index_;  // The index of the last frame in |audio_buffer|.
+  size_t max_frames_;  // The maximum input frames that |audio_buffer_|
+                       // can handle for each detection.
+
+  DISALLOW_COPY_AND_ASSIGN(RepetitionDetector);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_MEDIA_REPETITION_DETECTOR_H_