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diff --git a/webrtc/modules/audio_processing/agc2/signal_classifier.h b/webrtc/modules/audio_processing/agc2/signal_classifier.h
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+++ b/webrtc/modules/audio_processing/agc2/signal_classifier.h
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+/*
+ *  Copyright (c) 2016 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_PROCESSING_AGC2_SIGNAL_CLASSIFIER_H_
+#define MODULES_AUDIO_PROCESSING_AGC2_SIGNAL_CLASSIFIER_H_
+
+#include <memory>
+#include <vector>
+
+#include "api/array_view.h"
+#include "common_audio/third_party/ooura/fft_size_128/ooura_fft.h"
+#include "modules/audio_processing/agc2/down_sampler.h"
+#include "modules/audio_processing/agc2/noise_spectrum_estimator.h"
+
+namespace webrtc {
+
+class ApmDataDumper;
+class AudioBuffer;
+
+class SignalClassifier {
+ public:
+  enum class SignalType { kNonStationary, kStationary };
+
+  explicit SignalClassifier(ApmDataDumper* data_dumper);
+
+  SignalClassifier() = delete;
+  SignalClassifier(const SignalClassifier&) = delete;
+  SignalClassifier& operator=(const SignalClassifier&) = delete;
+
+  ~SignalClassifier();
+
+  void Initialize(int sample_rate_hz);
+  SignalType Analyze(rtc::ArrayView<const float> signal);
+
+ private:
+  class FrameExtender {
+   public:
+    FrameExtender(size_t frame_size, size_t extended_frame_size);
+
+    FrameExtender() = delete;
+    FrameExtender(const FrameExtender&) = delete;
+    FrameExtender& operator=(const FrameExtender&) = delete;
+
+    ~FrameExtender();
+
+    void ExtendFrame(rtc::ArrayView<const float> x,
+                     rtc::ArrayView<float> x_extended);
+
+   private:
+    std::vector<float> x_old_;
+  };
+
+  ApmDataDumper* const data_dumper_;
+  DownSampler down_sampler_;
+  std::unique_ptr<FrameExtender> frame_extender_;
+  NoiseSpectrumEstimator noise_spectrum_estimator_;
+  int sample_rate_hz_;
+  int initialization_frames_left_;
+  int consistent_classification_counter_;
+  SignalType last_signal_type_;
+  const OouraFft ooura_fft_;
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_AUDIO_PROCESSING_AGC2_SIGNAL_CLASSIFIER_H_