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      1 /*
      2  *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
      3  *
      4  *  Use of this source code is governed by a BSD-style license
      5  *  that can be found in the LICENSE file in the root of the source
      6  *  tree. An additional intellectual property rights grant can be found
      7  *  in the file PATENTS.  All contributing project authors may
      8  *  be found in the AUTHORS file in the root of the source tree.
      9  */
     10 
     11 #ifndef WEBRTC_MODULES_AUDIO_CODING_NETEQ_TIME_STRETCH_H_
     12 #define WEBRTC_MODULES_AUDIO_CODING_NETEQ_TIME_STRETCH_H_
     13 
     14 #include <assert.h>
     15 #include <string.h>  // memset, size_t
     16 
     17 #include "webrtc/base/constructormagic.h"
     18 #include "webrtc/modules/audio_coding/neteq/audio_multi_vector.h"
     19 #include "webrtc/typedefs.h"
     20 
     21 namespace webrtc {
     22 
     23 // Forward declarations.
     24 class BackgroundNoise;
     25 
     26 // This is the base class for Accelerate and PreemptiveExpand. This class
     27 // cannot be instantiated, but must be used through either of the derived
     28 // classes.
     29 class TimeStretch {
     30  public:
     31   enum ReturnCodes {
     32     kSuccess = 0,
     33     kSuccessLowEnergy = 1,
     34     kNoStretch = 2,
     35     kError = -1
     36   };
     37 
     38   TimeStretch(int sample_rate_hz, size_t num_channels,
     39               const BackgroundNoise& background_noise)
     40       : sample_rate_hz_(sample_rate_hz),
     41         fs_mult_(sample_rate_hz / 8000),
     42         num_channels_(static_cast<int>(num_channels)),
     43         master_channel_(0),  // First channel is master.
     44         background_noise_(background_noise),
     45         max_input_value_(0) {
     46     assert(sample_rate_hz_ == 8000 ||
     47            sample_rate_hz_ == 16000 ||
     48            sample_rate_hz_ == 32000 ||
     49            sample_rate_hz_ == 48000);
     50     assert(num_channels_ > 0);
     51     assert(static_cast<int>(master_channel_) < num_channels_);
     52     memset(auto_correlation_, 0, sizeof(auto_correlation_));
     53   }
     54 
     55   virtual ~TimeStretch() {}
     56 
     57   // This method performs the processing common to both Accelerate and
     58   // PreemptiveExpand.
     59   ReturnCodes Process(const int16_t* input,
     60                       size_t input_len,
     61                       AudioMultiVector* output,
     62                       int16_t* length_change_samples);
     63 
     64  protected:
     65   // Sets the parameters |best_correlation| and |peak_index| to suitable
     66   // values when the signal contains no active speech. This method must be
     67   // implemented by the sub-classes.
     68   virtual void SetParametersForPassiveSpeech(size_t input_length,
     69                                              int16_t* best_correlation,
     70                                              int* peak_index) const = 0;
     71 
     72   // Checks the criteria for performing the time-stretching operation and,
     73   // if possible, performs the time-stretching. This method must be implemented
     74   // by the sub-classes.
     75   virtual ReturnCodes CheckCriteriaAndStretch(
     76       const int16_t* input, size_t input_length, size_t peak_index,
     77       int16_t best_correlation, bool active_speech,
     78       AudioMultiVector* output) const = 0;
     79 
     80   static const int kCorrelationLen = 50;
     81   static const int kLogCorrelationLen = 6;  // >= log2(kCorrelationLen).
     82   static const int kMinLag = 10;
     83   static const int kMaxLag = 60;
     84   static const int kDownsampledLen = kCorrelationLen + kMaxLag;
     85   static const int kCorrelationThreshold = 14746;  // 0.9 in Q14.
     86 
     87   const int sample_rate_hz_;
     88   const int fs_mult_;  // Sample rate multiplier = sample_rate_hz_ / 8000.
     89   const int num_channels_;
     90   const size_t master_channel_;
     91   const BackgroundNoise& background_noise_;
     92   int16_t max_input_value_;
     93   int16_t downsampled_input_[kDownsampledLen];
     94   // Adding 1 to the size of |auto_correlation_| because of how it is used
     95   // by the peak-detection algorithm.
     96   int16_t auto_correlation_[kCorrelationLen + 1];
     97 
     98  private:
     99   // Calculates the auto-correlation of |downsampled_input_| and writes the
    100   // result to |auto_correlation_|.
    101   void AutoCorrelation();
    102 
    103   // Performs a simple voice-activity detection based on the input parameters.
    104   bool SpeechDetection(int32_t vec1_energy, int32_t vec2_energy,
    105                        int peak_index, int scaling) const;
    106 
    107   DISALLOW_COPY_AND_ASSIGN(TimeStretch);
    108 };
    109 
    110 }  // namespace webrtc
    111 #endif  // WEBRTC_MODULES_AUDIO_CODING_NETEQ_TIME_STRETCH_H_
    112