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diff --git a/third_party/libwebrtc/modules/video_coding/loss_notification_controller.h b/third_party/libwebrtc/modules/video_coding/loss_notification_controller.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 MODULES_VIDEO_CODING_LOSS_NOTIFICATION_CONTROLLER_H_
+#define MODULES_VIDEO_CODING_LOSS_NOTIFICATION_CONTROLLER_H_
+
+#include <stdint.h>
+
+#include <set>
+
+#include "absl/types/optional.h"
+#include "api/array_view.h"
+#include "api/sequence_checker.h"
+#include "modules/include/module_common_types.h"
+#include "rtc_base/system/no_unique_address.h"
+
+namespace webrtc {
+
+class LossNotificationController {
+ public:
+  struct FrameDetails {
+    bool is_keyframe;
+    int64_t frame_id;
+    rtc::ArrayView<const int64_t> frame_dependencies;
+  };
+
+  LossNotificationController(KeyFrameRequestSender* key_frame_request_sender,
+                             LossNotificationSender* loss_notification_sender);
+  ~LossNotificationController();
+
+  // An RTP packet was received from the network.
+  // `frame` is non-null iff the packet is the first packet in the frame.
+  void OnReceivedPacket(uint16_t rtp_seq_num, const FrameDetails* frame);
+
+  // A frame was assembled from packets previously received.
+  // (Should be called even if the frame was composed of a single packet.)
+  void OnAssembledFrame(uint16_t first_seq_num,
+                        int64_t frame_id,
+                        bool discardable,
+                        rtc::ArrayView<const int64_t> frame_dependencies);
+
+ private:
+  void DiscardOldInformation();
+
+  bool AllDependenciesDecodable(
+      rtc::ArrayView<const int64_t> frame_dependencies) const;
+
+  // When the loss of a packet or the non-decodability of a frame is detected,
+  // produces a key frame request or a loss notification.
+  // 1. `last_received_seq_num` is the last received sequence number.
+  // 2. `decodability_flag` refers to the frame associated with the last packet.
+  //    It is set to `true` if and only if all of that frame's dependencies are
+  //    known to be decodable, and the frame itself is not yet known to be
+  //    unassemblable (i.e. no earlier parts of it were lost).
+  //    Clarifications:
+  //    a. In a multi-packet frame, the first packet reveals the frame's
+  //       dependencies, but it is not yet known whether all parts of the
+  //       current frame will be received.
+  //    b. In a multi-packet frame, if the first packet is missed, the
+  //       dependencies are unknown, but it is known that the frame itself
+  //       is unassemblable.
+  void HandleLoss(uint16_t last_received_seq_num, bool decodability_flag);
+
+  KeyFrameRequestSender* const key_frame_request_sender_
+      RTC_GUARDED_BY(sequence_checker_);
+
+  LossNotificationSender* const loss_notification_sender_
+      RTC_GUARDED_BY(sequence_checker_);
+
+  // Tracked to avoid processing repeated frames (buggy/malicious remote).
+  absl::optional<int64_t> last_received_frame_id_
+      RTC_GUARDED_BY(sequence_checker_);
+
+  // Tracked to avoid processing repeated packets.
+  absl::optional<uint16_t> last_received_seq_num_
+      RTC_GUARDED_BY(sequence_checker_);
+
+  // Tracked in order to correctly report the potential-decodability of
+  // multi-packet frames.
+  bool current_frame_potentially_decodable_ RTC_GUARDED_BY(sequence_checker_);
+
+  // Loss notifications contain the sequence number of the first packet of
+  // the last decodable-and-non-discardable frame. Since this is a bit of
+  // a mouthful, last_decodable_non_discardable_.first_seq_num is used,
+  // which hopefully is a bit easier for human beings to parse
+  // than `first_seq_num_of_last_decodable_non_discardable_`.
+  struct FrameInfo {
+    explicit FrameInfo(uint16_t first_seq_num) : first_seq_num(first_seq_num) {}
+    uint16_t first_seq_num;
+  };
+  absl::optional<FrameInfo> last_decodable_non_discardable_
+      RTC_GUARDED_BY(sequence_checker_);
+
+  // Track which frames are decodable. Later frames are also decodable if
+  // all of their dependencies can be found in this container.
+  // (Naturally, later frames must also be assemblable to be decodable.)
+  std::set<int64_t> decodable_frame_ids_ RTC_GUARDED_BY(sequence_checker_);
+
+  RTC_NO_UNIQUE_ADDRESS SequenceChecker sequence_checker_;
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_VIDEO_CODING_LOSS_NOTIFICATION_CONTROLLER_H_