Add detection for repeated audio in capturing.

content/renderer/media/audio_repetition_detector.h

+// 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_AUDIO_REPETITION_DETECTOR_H_
+#define CONTENT_RENDERER_MEDIA_AUDIO_REPETITION_DETECTOR_H_
+
+#include <vector>
+
+#include "base/memory/scoped_vector.h"
+#include "base/threading/thread_checker.h"
+#include "content/common/content_export.h"
+
+namespace content {
+
+
+// AudioRepetitionDetector detects bit-exact audio repetitions of registered
+// patterns. A repetition pattern is defined by a look back time. The detector
+// buffers the audio signal and checks equality of each input sample against the
+// samples at the look back positions of all registered patterns, and counts the
+// duration of any consecutive equality.

[Henrik Grunell, 2015/10/16 07:59:50]

Re the dtor check hit, maybe comment on the threading and lifetime here?

[minyue, 2015/10/16 08:34:42]

Do you mean to write something like:

An instance of this class can only be used in one thread, although the
construction and deconstruction can be made in a different thread.

[Henrik Grunell, 2015/10/16 08:44:11]

Yes, something like that. And why destructing it on another thread than the
calls are made on is safe.

[minyue, 2015/10/16 09:27:28]

The failure in an earlier patch that triggered me to change the threading
checker seems to have the same reason as in 
https://code.google.com/p/chromium/codesearch#chromium/src/content/renderer/m...

[Henrik Grunell, 2015/10/16 11:08:12]

Yes, that's fine. I think it's good to document that the owner of this object
will ensure no calls from the audio thread after destruction. (If that's the
case.)

+class CONTENT_EXPORT AudioRepetitionDetector {
+ public:
+  AudioRepetitionDetector();
+  virtual ~AudioRepetitionDetector();
+
+  // Detect repetition in |data|. A UMA report is generated upon finding
+  // a repetition. |sample_rate| is measured in Hz.
+  void Detect(const float* data, size_t num_frames, size_t num_channels,
+              int sample_rate);
+
+ private:
+  friend class AudioRepetitionDetectorForTest;  // For testing.

[Henrik Grunell, 2015/10/16 07:59:50]

Nit: I think you can remove the comment, it's clear from the name it's for
testing.

[minyue, 2015/10/16 08:34:42]

Acknowledged.

+
+  // A state is used by the detector to keep track of a consecutive repetition,
+  // whether the samples in a repetition are all zeros, and whether a repetition
+  // has been reported.
+  class State {
+   public:
+    explicit State(int look_back_ms);
+
+    int look_back_ms() const { return look_back_ms_; };
+    size_t count_frames() const { return count_frames_; }
+    bool all_zero() const { return all_zero_; }
+    bool reported() const { return reported_; }
+    void set_reported(bool reported) { reported_ = reported; }
+
+    // Increase |count_frames_| by 1, and |zero| indidates whether the added
+    // audio frame is zero.
+    void Increment(bool zero);
+
+    void Reset();
+
+   private:
+    // Look back time of the repetition pattern this state keeps track of.
+    const int look_back_ms_;
+
+    // counter of frames in a consecutive repetition.

[Henrik Grunell, 2015/10/16 07:59:50]

Nit: begin with capital letter. Here and below.

[minyue, 2015/10/16 08:34:42]

Acknowledged.

+    size_t count_frames_;
+
+    // whether a repetition contains only zeros.
+    bool all_zero_;
+
+    // |reported_| tells whether a repetition has been reported. This is to make
+    // sure that a repetition with a long duration will be reported as early as
+    // being detected but no more than one time.
+    bool reported_;
+
+    DISALLOW_COPY_AND_ASSIGN(State);
+  };
+
+  void RegisterLookbackTime(int look_back_ms);
+
+  // Reset |audio_buffer_| when number of channels or sample rate (Hz) changes.
+  void Reset(size_t num_channels, int sample_rate);
+
+  // 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, size_t num_channels) const;
+
+  // Check whether the state contains a valid repetition report.
+  bool HasValidReport(const State* state) const;
+
+  // Action when found repetition.
+  virtual void ReportRepetition(int look_back_ms);
+
+  // Used to DCHECK that we are called on the correct thread.
+  base::ThreadChecker thread_checker_;
+
+  ScopedVector<State> states_;
+
+  // Ring buffer to store input audio.
+  std::vector<float> audio_buffer_;
+
+  // Maximum look back time of all registered repetitions. This defines the size
+  // of |audio_buffer_|
+  int max_look_back_ms_;
+
+  // The shortest length for repetitions.
+  int min_length_ms_;
+
+  // Number of audio channels in buffer.
+  size_t num_channels_;
+
+  // Sample rate in Hz.
+  int sample_rate_;
+
+  // Number of frames in |audio_buffer|.
+  size_t buffer_size_frames_;
+
+  // The index of the last frame in |audio_buffer|.
+  size_t buffer_end_index_;
+
+  // The maximum frames |audio_buffer_| can take in each time.
+  size_t max_frames_;
+
+  DISALLOW_COPY_AND_ASSIGN(AudioRepetitionDetector);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_MEDIA_AUDIO_REPETITION_DETECTOR_H_