time_stretch.h - mozsearch

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/*

 *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.

 *  Use of this source code is governed by a BSD-style license

 *  that can be found in the LICENSE file in the root of the source

 *  tree. An additional intellectual property rights grant can be found

 *  in the file PATENTS.  All contributing project authors may

 *  be found in the AUTHORS file in the root of the source tree.

*/

#ifndef MODULES_AUDIO_CODING_NETEQ_TIME_STRETCH_H_

#define MODULES_AUDIO_CODING_NETEQ_TIME_STRETCH_H_

#include <string.h>  // memset, size_t

#include "modules/audio_coding/neteq/audio_multi_vector.h"

namespace webrtc {

// Forward declarations.

class BackgroundNoise;

// This is the base class for Accelerate and PreemptiveExpand. This class

// cannot be instantiated, but must be used through either of the derived

// classes.

class TimeStretch {

 public:

  enum ReturnCodes {

    kSuccess = 0,

    kSuccessLowEnergy = 1,

    kNoStretch = 2,

    kError = -1

};

  TimeStretch(int sample_rate_hz,

              size_t num_channels,

              const BackgroundNoise& background_noise)

      : sample_rate_hz_(sample_rate_hz),

        fs_mult_(sample_rate_hz / 8000),

        num_channels_(num_channels),

        background_noise_(background_noise),

        max_input_value_(0) {

    RTC_DCHECK(sample_rate_hz_ == 8000 || sample_rate_hz_ == 16000 ||

               sample_rate_hz_ == 32000 || sample_rate_hz_ == 48000);

    RTC_DCHECK_GT(num_channels_, 0);

    memset(auto_correlation_, 0, sizeof(auto_correlation_));

  virtual ~TimeStretch() {}

  TimeStretch(const TimeStretch&) = delete;

  TimeStretch& operator=(const TimeStretch&) = delete;

  // This method performs the processing common to both Accelerate and

  // PreemptiveExpand.

  ReturnCodes Process(const int16_t* input,

                      size_t input_len,

                      bool fast_mode,

                      AudioMultiVector* output,

                      size_t* length_change_samples);

 protected:

  // Sets the parameters `best_correlation` and `peak_index` to suitable

  // values when the signal contains no active speech. This method must be

  // implemented by the sub-classes.

  virtual void SetParametersForPassiveSpeech(size_t input_length,

                                             int16_t* best_correlation,

                                             size_t* peak_index) const = 0;

  // Checks the criteria for performing the time-stretching operation and,

  // if possible, performs the time-stretching. This method must be implemented

  // by the sub-classes.

  virtual ReturnCodes CheckCriteriaAndStretch(

      const int16_t* input,

      size_t input_length,

      size_t peak_index,

      int16_t best_correlation,

      bool active_speech,

      bool fast_mode,

      AudioMultiVector* output) const = 0;

  static const size_t kCorrelationLen = 50;

  static const size_t kLogCorrelationLen = 6;  // >= log2(kCorrelationLen).

  static const size_t kMinLag = 10;

  static const size_t kMaxLag = 60;

  static const size_t kDownsampledLen = kCorrelationLen + kMaxLag;

  static const int kCorrelationThreshold = 14746;  // 0.9 in Q14.

  static constexpr size_t kRefChannel = 0;  // First channel is reference.

  const int sample_rate_hz_;

  const int fs_mult_;  // Sample rate multiplier = sample_rate_hz_ / 8000.

  const size_t num_channels_;

  const BackgroundNoise& background_noise_;

  int16_t max_input_value_;

  int16_t downsampled_input_[kDownsampledLen];

  // Adding 1 to the size of `auto_correlation_` because of how it is used

  // by the peak-detection algorithm.

  int16_t auto_correlation_[kCorrelationLen + 1];

 private:

  // Calculates the auto-correlation of `downsampled_input_` and writes the

  // result to `auto_correlation_`.

  void AutoCorrelation();

  // Performs a simple voice-activity detection based on the input parameters.

  bool SpeechDetection(int32_t vec1_energy,

                       int32_t vec2_energy,

                       size_t peak_index,

                       int scaling) const;

};

}  // namespace webrtc

#endif  // MODULES_AUDIO_CODING_NETEQ_TIME_STRETCH_H_