Add an endpointer for detecting end of speech.

chrome/browser/speech/endpointer/energy_endpointer.h

+// Copyright (c) 2010 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.
+
+// The EnergyEndpointer class finds likely speech onset and offset points.
+//
+// The implementation described here is about the simplest possible.
+// It is based on timings of threshold crossings for overall signal
+// RMS. It is suitable for light weight applications.
+//
+// As written, the basic idea is that one specifies intervals that
+// must be occupied by super- and sub-threshold energy levels, and
+// defers decisions re onset and offset times until these
+// specifications have been met.  Three basic intervals are tested: an
+// onset window, a speech-on window, and an offset window.  We require
+// super-threshold to exceed some mimimum total durations in the onset
+// and speech-on windows before declaring the speech onset time, and
+// we specify a required sub-threshold residency in the offset window
+// before declaring speech offset. As the various residency requirements are
+// met, the EnergyEndpointer instance assumes various states, and can return the
+// ID of these states to the client (see EpStatus below).
+//
+// The levels of the speech and background noise are continuously updated. It is
+// important that the background noise level be estimated initially for
+// robustness in noisy conditions. The first frames are assumed to be background
+// noise and a fast update rate is used for the noise level. The duration for
+// fast update is controlled by the fast_update_dur_ paramter.
+//
+// If used in noisy conditions, the endpointer should be started and run in the
+// EnvironmentEstimation mode, for at least 200ms, before switching to
+// UserInputMode.
+// Audio feedback contamination can appear in the input audio, if not cut
+// out or handled by echo cancellation. Audio feedback can trigger a false
+// accept. The false accepts can be ignored by setting
+// ep_contamination_rejection_period.
+
+#ifndef CHROME_BROWSER_SPEECH_ENDPOINTER_ENERGY_ENDPOINTER_H_
+#define CHROME_BROWSER_SPEECH_ENDPOINTER_ENERGY_ENDPOINTER_H_
+
+#include "base/basictypes.h"
+#include "base/scoped_ptr.h"
+#include "chrome/browser/speech/endpointer/energy_endpointer_params.h"
+#include <vector>
+
+namespace speech_input {
+
+// Endpointer status codes
+enum EpStatus {
+  EP_PRE_SPEECH = 10,
+  EP_POSSIBLE_ONSET,
+  EP_SPEECH_PRESENT,
+  EP_POSSIBLE_OFFSET,
+  EP_POST_SPEECH,
+};
+
+class EnergyEndpointer {
+ public:
+  // The default construction MUST be followed by Init(), before any
+  // other use can be made of the instance.
+  EnergyEndpointer();
+  virtual ~EnergyEndpointer();
+
+  void Init(const EnergyEndpointerParams& params);
+
+  // Start the endpointer. This should be called at the beginning of a session.
+  void StartSession();
+
+  // Stop the endpointer.
+  void EndSession();
+
+  // Start environment estimation. Audio will be used for environment estimation
+  // i.e. noise level estimation.
+  void SetEnvironmentEstimationMode();
+
+  // Start user input. This should be called when the user indicates start of
+  // input, e.g. by pressing a button.
+  void SetUserInputMode();
+
+  // Computes the next input frame and modifies EnergyEndpointer status as
+  // appropriate based on the computation.
+  void ProcessAudioFrame(int64 time_us, const int16* samples, int num_samples);
+
+  // Returns the current state of the EnergyEndpointer and the time
+  // corresponding to the most recently computed frame.
+  EpStatus Status(int64* status_time_us) const;
+
+ private:
+  class HistoryRing;
+
+  // Resets the endpointer internal state.  If reset_threshold is true, the
+  // state will be reset completely, including adaptive thresholds and the
+  // removal of all history information.
+  void Restart(bool reset_threshold);
+
+  // Update internal speech and noise levels.
+  void UpdateLevels(float rms);
+
+  // Returns the number of frames (or frame number) corresponding to
+  // the 'time' (in seconds).
+  int TimeToFrame(float time) const;
+
+  EpStatus status_;  // The current state of this instance.
+  float offset_confirm_dur_sec_;  // max on time allowed to confirm POST_SPEECH
+  int64 endpointer_time_us_;  // Time of the most recently received audio frame.
+  int64 fast_update_frames_; // Number of frames for initial level adaptation.
+  int64 frame_counter_;  // Number of frames seen. Used for initial adaptation.
+  float max_window_dur_;  // Largest search window size (seconds)
+  float sample_rate_;  // Sampling rate.
+
+  // Ring buffers to hold the speech activity history.
+  scoped_ptr<HistoryRing> history_;
+
+  // Configuration parameters.
+  EnergyEndpointerParams params_;
+
+  // RMS which must be exceeded to conclude frame is speech.
+  float decision_threshold_;
+
+  // Flag to indicate that audio should be used to estmiate enviroment, prior to
+  // receiving user input.
+  bool estimating_environment_;
+
+  // Estimate of the background noise level. Used externally for UI feedback.
+  float noise_level_;
+
+  // An adaptive threshold used to update decision_threshold_ when appropriate.
+  float rms_adapt_;
+
+  // Start lag corresponds to the highest fundamental frequency.
+  int start_lag_;
+
+  // End lag corresponds to the lowest fundamental frequency.
+  int end_lag_;
+
+  // Time when mode switched from environment estimation to user input. This
+  // is used to time forced rejection of audio feedback contamination.
+  int64 user_input_start_time_us_;
+
+  DISALLOW_COPY_AND_ASSIGN(EnergyEndpointer);
+};
+
+}  // namespace speech_input
+
+#endif  // CHROME_BROWSER_SPEECH_ENDPOINTER_ENERGY_ENDPOINTER_H_