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diff --git a/third_party/libwebrtc/video/unique_timestamp_counter.h b/third_party/libwebrtc/video/unique_timestamp_counter.h
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+++ b/third_party/libwebrtc/video/unique_timestamp_counter.h
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+/*
+ *  Copyright (c) 2019 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 VIDEO_UNIQUE_TIMESTAMP_COUNTER_H_
+#define VIDEO_UNIQUE_TIMESTAMP_COUNTER_H_
+
+#include <cstdint>
+#include <memory>
+#include <set>
+
+namespace webrtc {
+
+// Counts number of uniquely seen frames (aka pictures, aka temporal units)
+// identified by their rtp timestamp.
+class UniqueTimestampCounter {
+ public:
+  UniqueTimestampCounter();
+  UniqueTimestampCounter(const UniqueTimestampCounter&) = delete;
+  UniqueTimestampCounter& operator=(const UniqueTimestampCounter&) = delete;
+  ~UniqueTimestampCounter() = default;
+
+  void Add(uint32_t timestamp);
+  // Returns number of different `timestamp` passed to the UniqueCounter.
+  int GetUniqueSeen() const { return unique_seen_; }
+
+ private:
+  int unique_seen_ = 0;
+  // Stores several last seen unique values for quick search.
+  std::set<uint32_t> search_index_;
+  // The same unique values in the circular buffer in the insertion order.
+  std::unique_ptr<uint32_t[]> latest_;
+  // Last inserted value for optimization purpose.
+  int64_t last_ = -1;
+};
+
+}  // namespace webrtc
+
+#endif  // VIDEO_UNIQUE_TIMESTAMP_COUNTER_H_