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diff --git a/modules/audio_coding/neteq/time_stretch.h b/modules/audio_coding/neteq/time_stretch.h
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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 WEBRTC_MODULES_AUDIO_CODING_NETEQ_TIME_STRETCH_H_
+#define WEBRTC_MODULES_AUDIO_CODING_NETEQ_TIME_STRETCH_H_
+
+#include <assert.h>
+#include <string.h>  // memset, size_t
+
+#include "webrtc/base/constructormagic.h"
+#include "webrtc/modules/audio_coding/neteq/audio_multi_vector.h"
+#include "webrtc/typedefs.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_(static_cast<int>(num_channels)),
+        master_channel_(0),  // First channel is master.
+        background_noise_(background_noise),
+        max_input_value_(0) {
+    assert(sample_rate_hz_ == 8000 ||
+           sample_rate_hz_ == 16000 ||
+           sample_rate_hz_ == 32000 ||
+           sample_rate_hz_ == 48000);
+    assert(num_channels_ > 0);
+    assert(static_cast<int>(master_channel_) < num_channels_);
+    memset(auto_correlation_, 0, sizeof(auto_correlation_));
+  }
+
+  virtual ~TimeStretch() {}
+
+  // This method performs the processing common to both Accelerate and
+  // PreemptiveExpand.
+  ReturnCodes Process(const int16_t* input,
+                      size_t input_len,
+                      AudioMultiVector* output,
+                      int16_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,
+                                             int* 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,
+      AudioMultiVector* output) const = 0;
+
+  static const int kCorrelationLen = 50;
+  static const int kLogCorrelationLen = 6;  // >= log2(kCorrelationLen).
+  static const int kMinLag = 10;
+  static const int kMaxLag = 60;
+  static const int kDownsampledLen = kCorrelationLen + kMaxLag;
+  static const int kCorrelationThreshold = 14746;  // 0.9 in Q14.
+
+  const int sample_rate_hz_;
+  const int fs_mult_;  // Sample rate multiplier = sample_rate_hz_ / 8000.
+  const int num_channels_;
+  const size_t master_channel_;
+  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,
+                       int peak_index, int scaling) const;
+
+  DISALLOW_COPY_AND_ASSIGN(TimeStretch);
+};
+
+}  // namespace webrtc
+#endif  // WEBRTC_MODULES_AUDIO_CODING_NETEQ_TIME_STRETCH_H_