modules/video_coding/loss_notification_controller_unittest.cc - src - Git at Google

 /*
  *  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.
  */

 #include "modules/video_coding/loss_notification_controller.h"

 #include <stdint.h>

 #include <limits>
 #include <string>
 #include <tuple>
 #include <utility>
 #include <vector>

 #include "absl/types/optional.h"
 #include "test/gtest.h"

 namespace webrtc {
 namespace {

 // The information about an RTP packet that is relevant in these tests.
 struct Packet {
   uint16_t seq_num;
   bool first_in_frame;
   bool is_keyframe;
   int64_t frame_id;
   std::vector<int64_t> frame_dependencies;
 };

 Packet CreatePacket(
     bool first_in_frame,
     bool last_in_frame,
     uint16_t seq_num,
     uint16_t frame_id,
     bool is_key_frame,
     std::vector<int64_t> ref_frame_ids = std::vector<int64_t>()) {
   Packet packet;
   packet.seq_num = seq_num;
   packet.first_in_frame = first_in_frame;
   if (first_in_frame) {
     packet.is_keyframe = is_key_frame;
     packet.frame_id = frame_id;
     RTC_DCHECK(!is_key_frame || ref_frame_ids.empty());
     packet.frame_dependencies = std::move(ref_frame_ids);
   }
   return packet;
 }

 class PacketStreamCreator final {
  public:
   PacketStreamCreator() : seq_num_(0), frame_id_(0), next_is_key_frame_(true) {}

   Packet NextPacket() {
     std::vector<int64_t> ref_frame_ids;
     if (!next_is_key_frame_) {
       ref_frame_ids.push_back(frame_id_ - 1);
     }

     Packet packet = CreatePacket(true, true, seq_num_++, frame_id_++,
                                  next_is_key_frame_, ref_frame_ids);

     next_is_key_frame_ = false;

     return packet;
   }

  private:
   uint16_t seq_num_;
   int64_t frame_id_;
   bool next_is_key_frame_;
 };
 }  // namespace

 // Most of the logic for the tests is here. Subclasses allow parameterizing
 // the test, or adding some more specific logic.
 class LossNotificationControllerBaseTest : public ::testing::Test,
                                            public KeyFrameRequestSender,
                                            public LossNotificationSender {
  protected:
   LossNotificationControllerBaseTest()
       : uut_(this, this), key_frame_requested_(false) {}

   ~LossNotificationControllerBaseTest() override {
     EXPECT_FALSE(LastKeyFrameRequest());
     EXPECT_FALSE(LastLossNotification());
   }

   // KeyFrameRequestSender implementation.
   void RequestKeyFrame() override {
     EXPECT_FALSE(LastKeyFrameRequest());
     EXPECT_FALSE(LastLossNotification());
     key_frame_requested_ = true;
   }

   // LossNotificationSender implementation.
   void SendLossNotification(uint16_t last_decoded_seq_num,
                             uint16_t last_received_seq_num,
                             bool decodability_flag,
                             bool buffering_allowed) override {
     EXPECT_TRUE(buffering_allowed);  // (Flag useful elsewhere.)
     EXPECT_FALSE(LastKeyFrameRequest());
     EXPECT_FALSE(LastLossNotification());
     last_loss_notification_.emplace(last_decoded_seq_num, last_received_seq_num,
                                     decodability_flag);
   }

   void OnReceivedPacket(const Packet& packet) {
     EXPECT_FALSE(LastKeyFrameRequest());
     EXPECT_FALSE(LastLossNotification());

     if (packet.first_in_frame) {
       previous_first_packet_in_frame_ = packet;
       LossNotificationController::FrameDetails frame;
       frame.is_keyframe = packet.is_keyframe;
       frame.frame_id = packet.frame_id;
       frame.frame_dependencies = packet.frame_dependencies;
       uut_.OnReceivedPacket(packet.seq_num, &frame);
     } else {
       uut_.OnReceivedPacket(packet.seq_num, nullptr);
     }
   }

   void OnAssembledFrame(uint16_t first_seq_num,
                         int64_t frame_id,
                         bool discardable) {
     EXPECT_FALSE(LastKeyFrameRequest());
     EXPECT_FALSE(LastLossNotification());

     ASSERT_TRUE(previous_first_packet_in_frame_);
     uut_.OnAssembledFrame(first_seq_num, frame_id, discardable,
                           previous_first_packet_in_frame_->frame_dependencies);
   }

   void ExpectKeyFrameRequest() {
     EXPECT_EQ(LastLossNotification(), absl::nullopt);
     EXPECT_TRUE(LastKeyFrameRequest());
   }

   void ExpectLossNotification(uint16_t last_decoded_seq_num,
                               uint16_t last_received_seq_num,
                               bool decodability_flag) {
     EXPECT_FALSE(LastKeyFrameRequest());
     const auto last_ln = LastLossNotification();
     ASSERT_TRUE(last_ln);
     const LossNotification expected_ln(
         last_decoded_seq_num, last_received_seq_num, decodability_flag);
     EXPECT_EQ(expected_ln, *last_ln)
         << "Expected loss notification (" << expected_ln.ToString()
         << ") != received loss notification (" << last_ln->ToString() + ")";
   }

   struct LossNotification {
     LossNotification(uint16_t last_decoded_seq_num,
                      uint16_t last_received_seq_num,
                      bool decodability_flag)
         : last_decoded_seq_num(last_decoded_seq_num),
           last_received_seq_num(last_received_seq_num),
           decodability_flag(decodability_flag) {}

     LossNotification& operator=(const LossNotification& other) = default;

     bool operator==(const LossNotification& other) const {
       return last_decoded_seq_num == other.last_decoded_seq_num &&
              last_received_seq_num == other.last_received_seq_num &&
              decodability_flag == other.decodability_flag;
     }

     std::string ToString() const {
       return std::to_string(last_decoded_seq_num) + ", " +
              std::to_string(last_received_seq_num) + ", " +
              std::to_string(decodability_flag);
     }

     uint16_t last_decoded_seq_num;
     uint16_t last_received_seq_num;
     bool decodability_flag;
   };

   bool LastKeyFrameRequest() {
     const bool result = key_frame_requested_;
     key_frame_requested_ = false;
     return result;
   }

   absl::optional<LossNotification> LastLossNotification() {
     const absl::optional<LossNotification> result = last_loss_notification_;
     last_loss_notification_ = absl::nullopt;
     return result;
   }

   LossNotificationController uut_;  // Unit under test.

   bool key_frame_requested_;

   absl::optional<LossNotification> last_loss_notification_;

   // First packet of last frame. (Note that if a test skips the first packet
   // of a subsequent frame, OnAssembledFrame is not called, and so this is
   // note read. Therefore, it's not a problem if it is not cleared when
   // the frame changes.)
   absl::optional<Packet> previous_first_packet_in_frame_;
 };

 class LossNotificationControllerTest
     : public LossNotificationControllerBaseTest,
       public ::testing::WithParamInterface<std::tuple<bool, bool, bool>> {
  protected:
   // Arbitrary parameterized values, to be used by the tests whenever they
   // wish to either check some combinations, or wish to demonstrate that
   // a particular arbitrary value is unimportant.
   template <size_t N>
   bool Bool() const {
     return std::get<N>(GetParam());
   }
 };

 INSTANTIATE_TEST_SUITE_P(_,
                          LossNotificationControllerTest,
                          ::testing::Combine(::testing::Bool(),
                                             ::testing::Bool(),
                                             ::testing::Bool()));

 // If the first frame, which is a key frame, is lost, then a new key frame
 // is requested.
 TEST_P(LossNotificationControllerTest,
        PacketLossBeforeFirstFrameAssembledTriggersKeyFrameRequest) {
   OnReceivedPacket(CreatePacket(true, false, 100, 0, true));
   OnReceivedPacket(CreatePacket(Bool<0>(), Bool<1>(), 103, 1, false, {0}));
   ExpectKeyFrameRequest();
 }

 // If packet loss occurs (but not of the first packet), then a loss notification
 // is issued.
 TEST_P(LossNotificationControllerTest,
        PacketLossAfterFirstFrameAssembledTriggersLossNotification) {
   OnReceivedPacket(CreatePacket(true, true, 100, 0, true));
   OnAssembledFrame(100, 0, false);
   const bool first = Bool<0>();
   const bool last = Bool<1>();
   OnReceivedPacket(CreatePacket(first, last, 103, 1, false, {0}));
   const bool expected_decodability_flag = first;
   ExpectLossNotification(100, 103, expected_decodability_flag);
 }

 // No key frame or loss notifications issued due to an innocuous wrap-around
 // of the sequence number.
 TEST_P(LossNotificationControllerTest, SeqNumWrapAround) {
   uint16_t seq_num = std::numeric_limits<uint16_t>::max();
   OnReceivedPacket(CreatePacket(true, true, seq_num, 0, true));
   OnAssembledFrame(seq_num, 0, false);
   const bool first = Bool<0>();
   const bool last = Bool<1>();
   OnReceivedPacket(CreatePacket(first, last, ++seq_num, 1, false, {0}));
 }

 TEST_F(LossNotificationControllerTest,
        KeyFrameAfterPacketLossProducesNoLossNotifications) {
   OnReceivedPacket(CreatePacket(true, true, 100, 1, true));
   OnAssembledFrame(100, 1, false);
   OnReceivedPacket(CreatePacket(true, true, 108, 8, true));
 }

 TEST_P(LossNotificationControllerTest, LostReferenceProducesLossNotification) {
   OnReceivedPacket(CreatePacket(true, true, 100, 0, true));
   OnAssembledFrame(100, 0, false);
   uint16_t last_decodable_non_discardable_seq_num = 100;

   // RTP gap produces loss notification - not the focus of this test.
   const bool first = Bool<0>();
   const bool last = Bool<1>();
   const bool discardable = Bool<2>();
   const bool decodable = first;  // Depends on assemblability.
   OnReceivedPacket(CreatePacket(first, last, 107, 3, false, {0}));
   ExpectLossNotification(100, 107, decodable);
   OnAssembledFrame(107, 3, discardable);
   if (!discardable) {
     last_decodable_non_discardable_seq_num = 107;
   }

   // Test focus - a loss notification is produced because of the missing
   // dependency (frame ID 2), despite the RTP sequence number being the
   // next expected one.
   OnReceivedPacket(CreatePacket(true, true, 108, 4, false, {2, 0}));
   ExpectLossNotification(last_decodable_non_discardable_seq_num, 108, false);
 }

 // The difference between this test and the previous one, is that in this test,
 // although the reference frame was received, it was not decodable.
 TEST_P(LossNotificationControllerTest,
        UndecodableReferenceProducesLossNotification) {
   OnReceivedPacket(CreatePacket(true, true, 100, 0, true));
   OnAssembledFrame(100, 0, false);
   uint16_t last_decodable_non_discardable_seq_num = 100;

   // RTP gap produces loss notification - not the focus of this test.
   // Also, not decodable; this is important for later in the test.
   OnReceivedPacket(CreatePacket(true, true, 107, 3, false, {2}));
   ExpectLossNotification(100, 107, false);
   const bool discardable = Bool<0>();
   OnAssembledFrame(107, 3, discardable);

   // Test focus - a loss notification is produced because of the undecodable
   // dependency (frame ID 3, which depended on the missing frame ID 2).
   OnReceivedPacket(CreatePacket(true, true, 108, 4, false, {3, 0}));
   ExpectLossNotification(last_decodable_non_discardable_seq_num, 108, false);
 }

 TEST_P(LossNotificationControllerTest, RobustnessAgainstHighInitialRefFrameId) {
   constexpr uint16_t max_uint16_t = std::numeric_limits<uint16_t>::max();
   OnReceivedPacket(CreatePacket(true, true, 100, 0, true));
   OnAssembledFrame(100, 0, false);
   OnReceivedPacket(CreatePacket(true, true, 101, 1, false, {max_uint16_t}));
   ExpectLossNotification(100, 101, false);
   OnAssembledFrame(101, max_uint16_t, Bool<0>());
 }

 TEST_P(LossNotificationControllerTest, RepeatedPacketsAreIgnored) {
   PacketStreamCreator packet_stream;

   const auto key_frame_packet = packet_stream.NextPacket();
   OnReceivedPacket(key_frame_packet);
   OnAssembledFrame(key_frame_packet.seq_num, key_frame_packet.frame_id, false);

   const bool gap = Bool<0>();

   if (gap) {
     // Lose one packet.
     packet_stream.NextPacket();
   }

   auto repeated_packet = packet_stream.NextPacket();
   OnReceivedPacket(repeated_packet);
   if (gap) {
     // Loss notification issued because of the gap. This is not the focus of
     // the test.
     ExpectLossNotification(key_frame_packet.seq_num, repeated_packet.seq_num,
                            false);
   }
   OnReceivedPacket(repeated_packet);
 }

 TEST_F(LossNotificationControllerTest,
        RecognizesDependencyAcrossIntraFrameThatIsNotAKeyframe) {
   int last_seq_num = 1;
   auto receive = [&](bool is_key_frame, int64_t frame_id,
                      std::vector<int64_t> ref_frame_ids) {
     ++last_seq_num;
     OnReceivedPacket(CreatePacket(
         /*first_in_frame=*/true, /*last_in_frame=*/true, last_seq_num, frame_id,
         is_key_frame, std::move(ref_frame_ids)));
     OnAssembledFrame(last_seq_num, frame_id, /*discardable=*/false);
   };
   //  11 -- 13
   //   |     |
   //  10    12
   receive(/*is_key_frame=*/true, /*frame_id=*/10, /*ref_frame_ids=*/{});
   receive(/*is_key_frame=*/false, /*frame_id=*/11, /*ref_frame_ids=*/{10});
   receive(/*is_key_frame=*/false, /*frame_id=*/12, /*ref_frame_ids=*/{});
   receive(/*is_key_frame=*/false, /*frame_id=*/13, /*ref_frame_ids=*/{11, 12});
   EXPECT_FALSE(LastLossNotification());
 }

 class LossNotificationControllerTestDecodabilityFlag
     : public LossNotificationControllerBaseTest {
  protected:
   LossNotificationControllerTestDecodabilityFlag()
       : key_frame_seq_num_(100),
         key_frame_frame_id_(0),
         never_received_frame_id_(key_frame_frame_id_ + 1),
         seq_num_(0),
         frame_id_(0) {}

   void ReceiveKeyFrame() {
     RTC_DCHECK_NE(key_frame_frame_id_, never_received_frame_id_);
     OnReceivedPacket(CreatePacket(true, true, key_frame_seq_num_,
                                   key_frame_frame_id_, true));
     OnAssembledFrame(key_frame_seq_num_, key_frame_frame_id_, false);
     seq_num_ = key_frame_seq_num_;
     frame_id_ = key_frame_frame_id_;
   }

   void ReceivePacket(bool first_packet_in_frame,
                      bool last_packet_in_frame,
                      const std::vector<int64_t>& ref_frame_ids) {
     if (first_packet_in_frame) {
       frame_id_ += 1;
     }
     RTC_DCHECK_NE(frame_id_, never_received_frame_id_);
     constexpr bool is_key_frame = false;
     OnReceivedPacket(CreatePacket(first_packet_in_frame, last_packet_in_frame,
                                   ++seq_num_, frame_id_, is_key_frame,
                                   ref_frame_ids));
   }

   void CreateGap() {
     seq_num_ += 50;
     frame_id_ += 10;
   }

   const uint16_t key_frame_seq_num_;
   const uint16_t key_frame_frame_id_;

   // The tests intentionally never receive this, and can therefore always
   // use this as an unsatisfied dependency.
   const int64_t never_received_frame_id_ = 123;

   uint16_t seq_num_;
   int64_t frame_id_;
 };

 TEST_F(LossNotificationControllerTestDecodabilityFlag,
        SinglePacketFrameWithDecodableDependencies) {
   ReceiveKeyFrame();
   CreateGap();

   const std::vector<int64_t> ref_frame_ids = {key_frame_frame_id_};
   ReceivePacket(true, true, ref_frame_ids);

   const bool expected_decodability_flag = true;
   ExpectLossNotification(key_frame_seq_num_, seq_num_,
                          expected_decodability_flag);
 }

 TEST_F(LossNotificationControllerTestDecodabilityFlag,
        SinglePacketFrameWithUndecodableDependencies) {
   ReceiveKeyFrame();
   CreateGap();

   const std::vector<int64_t> ref_frame_ids = {never_received_frame_id_};
   ReceivePacket(true, true, ref_frame_ids);

   const bool expected_decodability_flag = false;
   ExpectLossNotification(key_frame_seq_num_, seq_num_,
                          expected_decodability_flag);
 }

 TEST_F(LossNotificationControllerTestDecodabilityFlag,
        FirstPacketOfMultiPacketFrameWithDecodableDependencies) {
   ReceiveKeyFrame();
   CreateGap();

   const std::vector<int64_t> ref_frame_ids = {key_frame_frame_id_};
   ReceivePacket(true, false, ref_frame_ids);

   const bool expected_decodability_flag = true;
   ExpectLossNotification(key_frame_seq_num_, seq_num_,
                          expected_decodability_flag);
 }

 TEST_F(LossNotificationControllerTestDecodabilityFlag,
        FirstPacketOfMultiPacketFrameWithUndecodableDependencies) {
   ReceiveKeyFrame();
   CreateGap();

   const std::vector<int64_t> ref_frame_ids = {never_received_frame_id_};
   ReceivePacket(true, false, ref_frame_ids);

   const bool expected_decodability_flag = false;
   ExpectLossNotification(key_frame_seq_num_, seq_num_,
                          expected_decodability_flag);
 }

 TEST_F(LossNotificationControllerTestDecodabilityFlag,
        MiddlePacketOfMultiPacketFrameWithDecodableDependenciesIfFirstMissed) {
   ReceiveKeyFrame();
   CreateGap();

   const std::vector<int64_t> ref_frame_ids = {key_frame_frame_id_};
   ReceivePacket(false, false, ref_frame_ids);

   const bool expected_decodability_flag = false;
   ExpectLossNotification(key_frame_seq_num_, seq_num_,
                          expected_decodability_flag);
 }

 TEST_F(LossNotificationControllerTestDecodabilityFlag,
        MiddlePacketOfMultiPacketFrameWithUndecodableDependenciesIfFirstMissed) {
   ReceiveKeyFrame();
   CreateGap();

   const std::vector<int64_t> ref_frame_ids = {never_received_frame_id_};
   ReceivePacket(false, false, ref_frame_ids);

   const bool expected_decodability_flag = false;
   ExpectLossNotification(key_frame_seq_num_, seq_num_,
                          expected_decodability_flag);
 }

 TEST_F(LossNotificationControllerTestDecodabilityFlag,
        MiddlePacketOfMultiPacketFrameWithDecodableDependenciesIfFirstReceived) {
   ReceiveKeyFrame();
   CreateGap();

   // First packet in multi-packet frame. A loss notification is produced
   // because of the gap in RTP sequence numbers.
   const std::vector<int64_t> ref_frame_ids = {key_frame_frame_id_};
   ReceivePacket(true, false, ref_frame_ids);
   const bool expected_decodability_flag_first = true;
   ExpectLossNotification(key_frame_seq_num_, seq_num_,
                          expected_decodability_flag_first);

   // Middle packet in multi-packet frame. No additional gap and the frame is
   // still potentially decodable, so no additional loss indication.
   ReceivePacket(false, false, ref_frame_ids);
   EXPECT_FALSE(LastKeyFrameRequest());
   EXPECT_FALSE(LastLossNotification());
 }

 TEST_F(
     LossNotificationControllerTestDecodabilityFlag,
     MiddlePacketOfMultiPacketFrameWithUndecodableDependenciesIfFirstReceived) {
   ReceiveKeyFrame();
   CreateGap();

   // First packet in multi-packet frame. A loss notification is produced
   // because of the gap in RTP sequence numbers. The frame is also recognized
   // as having non-decodable dependencies.
   const std::vector<int64_t> ref_frame_ids = {never_received_frame_id_};
   ReceivePacket(true, false, ref_frame_ids);
   const bool expected_decodability_flag_first = false;
   ExpectLossNotification(key_frame_seq_num_, seq_num_,
                          expected_decodability_flag_first);

   // Middle packet in multi-packet frame. No additional gap, but the frame is
   // known to be non-decodable, so we keep issuing loss indications.
   ReceivePacket(false, false, ref_frame_ids);
   const bool expected_decodability_flag_middle = false;
   ExpectLossNotification(key_frame_seq_num_, seq_num_,
                          expected_decodability_flag_middle);
 }

 TEST_F(LossNotificationControllerTestDecodabilityFlag,
        LastPacketOfMultiPacketFrameWithDecodableDependenciesIfAllPrevMissed) {
   ReceiveKeyFrame();
   CreateGap();

   const std::vector<int64_t> ref_frame_ids = {key_frame_frame_id_};
   ReceivePacket(false, true, ref_frame_ids);

   const bool expected_decodability_flag = false;
   ExpectLossNotification(key_frame_seq_num_, seq_num_,
                          expected_decodability_flag);
 }

 TEST_F(LossNotificationControllerTestDecodabilityFlag,
        LastPacketOfMultiPacketFrameWithUndecodableDependenciesIfAllPrevMissed) {
   ReceiveKeyFrame();
   CreateGap();

   const std::vector<int64_t> ref_frame_ids = {never_received_frame_id_};
   ReceivePacket(false, true, ref_frame_ids);

   const bool expected_decodability_flag = false;
   ExpectLossNotification(key_frame_seq_num_, seq_num_,
                          expected_decodability_flag);
 }

 TEST_F(LossNotificationControllerTestDecodabilityFlag,
        LastPacketOfMultiPacketFrameWithDecodableDependenciesIfAllPrevReceived) {
   ReceiveKeyFrame();
   CreateGap();

   // First packet in multi-packet frame. A loss notification is produced
   // because of the gap in RTP sequence numbers.
   const std::vector<int64_t> ref_frame_ids = {key_frame_frame_id_};
   ReceivePacket(true, false, ref_frame_ids);
   const bool expected_decodability_flag_first = true;
   ExpectLossNotification(key_frame_seq_num_, seq_num_,
                          expected_decodability_flag_first);

   // Last packet in multi-packet frame. No additional gap and the frame is
   // still potentially decodable, so no additional loss indication.
   ReceivePacket(false, true, ref_frame_ids);
   EXPECT_FALSE(LastKeyFrameRequest());
   EXPECT_FALSE(LastLossNotification());
 }

 TEST_F(
     LossNotificationControllerTestDecodabilityFlag,
     LastPacketOfMultiPacketFrameWithUndecodableDependenciesIfAllPrevReceived) {
   ReceiveKeyFrame();
   CreateGap();

   // First packet in multi-packet frame. A loss notification is produced
   // because of the gap in RTP sequence numbers. The frame is also recognized
   // as having non-decodable dependencies.
   const std::vector<int64_t> ref_frame_ids = {never_received_frame_id_};
   ReceivePacket(true, false, ref_frame_ids);
   const bool expected_decodability_flag_first = false;
   ExpectLossNotification(key_frame_seq_num_, seq_num_,
                          expected_decodability_flag_first);

   // Last packet in multi-packet frame. No additional gap, but the frame is
   // known to be non-decodable, so we keep issuing loss indications.
   ReceivePacket(false, true, ref_frame_ids);
   const bool expected_decodability_flag_last = false;
   ExpectLossNotification(key_frame_seq_num_, seq_num_,
                          expected_decodability_flag_last);
 }

 }  //  namespace webrtc
	/*
	* 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.
	*/

	#include "modules/video_coding/loss_notification_controller.h"

	#include <stdint.h>

	#include <limits>
	#include <string>
	#include <tuple>
	#include <utility>
	#include <vector>

	#include "absl/types/optional.h"
	#include "test/gtest.h"

	namespace webrtc {
	namespace {

	// The information about an RTP packet that is relevant in these tests.
	struct Packet {
	uint16_t seq_num;
	bool first_in_frame;
	bool is_keyframe;
	int64_t frame_id;
	std::vector<int64_t> frame_dependencies;
	};

	Packet CreatePacket(
	bool first_in_frame,
	bool last_in_frame,
	uint16_t seq_num,
	uint16_t frame_id,
	bool is_key_frame,
	std::vector<int64_t> ref_frame_ids = std::vector<int64_t>()) {
	Packet packet;
	packet.seq_num = seq_num;
	packet.first_in_frame = first_in_frame;
	if (first_in_frame) {
	packet.is_keyframe = is_key_frame;
	packet.frame_id = frame_id;
	RTC_DCHECK(!is_key_frame \|\| ref_frame_ids.empty());
	packet.frame_dependencies = std::move(ref_frame_ids);
	}
	return packet;
	}

	class PacketStreamCreator final {
	public:
	PacketStreamCreator() : seq_num_(0), frame_id_(0), next_is_key_frame_(true) {}

	Packet NextPacket() {
	std::vector<int64_t> ref_frame_ids;
	if (!next_is_key_frame_) {
	ref_frame_ids.push_back(frame_id_ - 1);
	}

	Packet packet = CreatePacket(true, true, seq_num_++, frame_id_++,
	next_is_key_frame_, ref_frame_ids);

	next_is_key_frame_ = false;

	return packet;
	}

	private:
	uint16_t seq_num_;
	int64_t frame_id_;
	bool next_is_key_frame_;
	};
	} // namespace

	// Most of the logic for the tests is here. Subclasses allow parameterizing
	// the test, or adding some more specific logic.
	class LossNotificationControllerBaseTest : public ::testing::Test,
	public KeyFrameRequestSender,
	public LossNotificationSender {
	protected:
	LossNotificationControllerBaseTest()
	: uut_(this, this), key_frame_requested_(false) {}

	~LossNotificationControllerBaseTest() override {
	EXPECT_FALSE(LastKeyFrameRequest());
	EXPECT_FALSE(LastLossNotification());
	}

	// KeyFrameRequestSender implementation.
	void RequestKeyFrame() override {
	EXPECT_FALSE(LastKeyFrameRequest());
	EXPECT_FALSE(LastLossNotification());
	key_frame_requested_ = true;
	}

	// LossNotificationSender implementation.
	void SendLossNotification(uint16_t last_decoded_seq_num,
	uint16_t last_received_seq_num,
	bool decodability_flag,
	bool buffering_allowed) override {
	EXPECT_TRUE(buffering_allowed); // (Flag useful elsewhere.)
	EXPECT_FALSE(LastKeyFrameRequest());
	EXPECT_FALSE(LastLossNotification());
	last_loss_notification_.emplace(last_decoded_seq_num, last_received_seq_num,
	decodability_flag);
	}

	void OnReceivedPacket(const Packet& packet) {
	EXPECT_FALSE(LastKeyFrameRequest());
	EXPECT_FALSE(LastLossNotification());

	if (packet.first_in_frame) {
	previous_first_packet_in_frame_ = packet;
	LossNotificationController::FrameDetails frame;
	frame.is_keyframe = packet.is_keyframe;
	frame.frame_id = packet.frame_id;
	frame.frame_dependencies = packet.frame_dependencies;
	uut_.OnReceivedPacket(packet.seq_num, &frame);
	} else {
	uut_.OnReceivedPacket(packet.seq_num, nullptr);
	}
	}

	void OnAssembledFrame(uint16_t first_seq_num,
	int64_t frame_id,
	bool discardable) {
	EXPECT_FALSE(LastKeyFrameRequest());
	EXPECT_FALSE(LastLossNotification());

	ASSERT_TRUE(previous_first_packet_in_frame_);
	uut_.OnAssembledFrame(first_seq_num, frame_id, discardable,
	previous_first_packet_in_frame_->frame_dependencies);
	}

	void ExpectKeyFrameRequest() {
	EXPECT_EQ(LastLossNotification(), absl::nullopt);
	EXPECT_TRUE(LastKeyFrameRequest());
	}

	void ExpectLossNotification(uint16_t last_decoded_seq_num,
	uint16_t last_received_seq_num,
	bool decodability_flag) {
	EXPECT_FALSE(LastKeyFrameRequest());
	const auto last_ln = LastLossNotification();
	ASSERT_TRUE(last_ln);
	const LossNotification expected_ln(
	last_decoded_seq_num, last_received_seq_num, decodability_flag);
	EXPECT_EQ(expected_ln, *last_ln)
	<< "Expected loss notification (" << expected_ln.ToString()
	<< ") != received loss notification (" << last_ln->ToString() + ")";
	}

	struct LossNotification {
	LossNotification(uint16_t last_decoded_seq_num,
	uint16_t last_received_seq_num,
	bool decodability_flag)
	: last_decoded_seq_num(last_decoded_seq_num),
	last_received_seq_num(last_received_seq_num),
	decodability_flag(decodability_flag) {}

	LossNotification& operator=(const LossNotification& other) = default;

	bool operator==(const LossNotification& other) const {
	return last_decoded_seq_num == other.last_decoded_seq_num &&
	last_received_seq_num == other.last_received_seq_num &&
	decodability_flag == other.decodability_flag;
	}

	std::string ToString() const {
	return std::to_string(last_decoded_seq_num) + ", " +
	std::to_string(last_received_seq_num) + ", " +
	std::to_string(decodability_flag);
	}

	uint16_t last_decoded_seq_num;
	uint16_t last_received_seq_num;
	bool decodability_flag;
	};

	bool LastKeyFrameRequest() {
	const bool result = key_frame_requested_;
	key_frame_requested_ = false;
	return result;
	}

	absl::optional<LossNotification> LastLossNotification() {
	const absl::optional<LossNotification> result = last_loss_notification_;
	last_loss_notification_ = absl::nullopt;
	return result;
	}

	LossNotificationController uut_; // Unit under test.

	bool key_frame_requested_;

	absl::optional<LossNotification> last_loss_notification_;

	// First packet of last frame. (Note that if a test skips the first packet
	// of a subsequent frame, OnAssembledFrame is not called, and so this is
	// note read. Therefore, it's not a problem if it is not cleared when
	// the frame changes.)
	absl::optional<Packet> previous_first_packet_in_frame_;
	};

	class LossNotificationControllerTest
	: public LossNotificationControllerBaseTest,
	public ::testing::WithParamInterface<std::tuple<bool, bool, bool>> {
	protected:
	// Arbitrary parameterized values, to be used by the tests whenever they
	// wish to either check some combinations, or wish to demonstrate that
	// a particular arbitrary value is unimportant.
	template <size_t N>
	bool Bool() const {
	return std::get<N>(GetParam());
	}
	};

	INSTANTIATE_TEST_SUITE_P(_,
	LossNotificationControllerTest,
	::testing::Combine(::testing::Bool(),
	::testing::Bool(),
	::testing::Bool()));

	// If the first frame, which is a key frame, is lost, then a new key frame
	// is requested.
	TEST_P(LossNotificationControllerTest,
	PacketLossBeforeFirstFrameAssembledTriggersKeyFrameRequest) {
	OnReceivedPacket(CreatePacket(true, false, 100, 0, true));
	OnReceivedPacket(CreatePacket(Bool<0>(), Bool<1>(), 103, 1, false, {0}));
	ExpectKeyFrameRequest();
	}

	// If packet loss occurs (but not of the first packet), then a loss notification
	// is issued.
	TEST_P(LossNotificationControllerTest,
	PacketLossAfterFirstFrameAssembledTriggersLossNotification) {
	OnReceivedPacket(CreatePacket(true, true, 100, 0, true));
	OnAssembledFrame(100, 0, false);
	const bool first = Bool<0>();
	const bool last = Bool<1>();
	OnReceivedPacket(CreatePacket(first, last, 103, 1, false, {0}));
	const bool expected_decodability_flag = first;
	ExpectLossNotification(100, 103, expected_decodability_flag);
	}

	// No key frame or loss notifications issued due to an innocuous wrap-around
	// of the sequence number.
	TEST_P(LossNotificationControllerTest, SeqNumWrapAround) {
	uint16_t seq_num = std::numeric_limits<uint16_t>::max();
	OnReceivedPacket(CreatePacket(true, true, seq_num, 0, true));
	OnAssembledFrame(seq_num, 0, false);
	const bool first = Bool<0>();
	const bool last = Bool<1>();
	OnReceivedPacket(CreatePacket(first, last, ++seq_num, 1, false, {0}));
	}

	TEST_F(LossNotificationControllerTest,
	KeyFrameAfterPacketLossProducesNoLossNotifications) {
	OnReceivedPacket(CreatePacket(true, true, 100, 1, true));
	OnAssembledFrame(100, 1, false);
	OnReceivedPacket(CreatePacket(true, true, 108, 8, true));
	}

	TEST_P(LossNotificationControllerTest, LostReferenceProducesLossNotification) {
	OnReceivedPacket(CreatePacket(true, true, 100, 0, true));
	OnAssembledFrame(100, 0, false);
	uint16_t last_decodable_non_discardable_seq_num = 100;

	// RTP gap produces loss notification - not the focus of this test.
	const bool first = Bool<0>();
	const bool last = Bool<1>();
	const bool discardable = Bool<2>();
	const bool decodable = first; // Depends on assemblability.
	OnReceivedPacket(CreatePacket(first, last, 107, 3, false, {0}));
	ExpectLossNotification(100, 107, decodable);
	OnAssembledFrame(107, 3, discardable);
	if (!discardable) {
	last_decodable_non_discardable_seq_num = 107;
	}

	// Test focus - a loss notification is produced because of the missing
	// dependency (frame ID 2), despite the RTP sequence number being the
	// next expected one.
	OnReceivedPacket(CreatePacket(true, true, 108, 4, false, {2, 0}));
	ExpectLossNotification(last_decodable_non_discardable_seq_num, 108, false);
	}

	// The difference between this test and the previous one, is that in this test,
	// although the reference frame was received, it was not decodable.
	TEST_P(LossNotificationControllerTest,
	UndecodableReferenceProducesLossNotification) {
	OnReceivedPacket(CreatePacket(true, true, 100, 0, true));
	OnAssembledFrame(100, 0, false);
	uint16_t last_decodable_non_discardable_seq_num = 100;

	// RTP gap produces loss notification - not the focus of this test.
	// Also, not decodable; this is important for later in the test.
	OnReceivedPacket(CreatePacket(true, true, 107, 3, false, {2}));
	ExpectLossNotification(100, 107, false);
	const bool discardable = Bool<0>();
	OnAssembledFrame(107, 3, discardable);

	// Test focus - a loss notification is produced because of the undecodable
	// dependency (frame ID 3, which depended on the missing frame ID 2).
	OnReceivedPacket(CreatePacket(true, true, 108, 4, false, {3, 0}));
	ExpectLossNotification(last_decodable_non_discardable_seq_num, 108, false);
	}

	TEST_P(LossNotificationControllerTest, RobustnessAgainstHighInitialRefFrameId) {
	constexpr uint16_t max_uint16_t = std::numeric_limits<uint16_t>::max();
	OnReceivedPacket(CreatePacket(true, true, 100, 0, true));
	OnAssembledFrame(100, 0, false);
	OnReceivedPacket(CreatePacket(true, true, 101, 1, false, {max_uint16_t}));
	ExpectLossNotification(100, 101, false);
	OnAssembledFrame(101, max_uint16_t, Bool<0>());
	}

	TEST_P(LossNotificationControllerTest, RepeatedPacketsAreIgnored) {
	PacketStreamCreator packet_stream;

	const auto key_frame_packet = packet_stream.NextPacket();
	OnReceivedPacket(key_frame_packet);
	OnAssembledFrame(key_frame_packet.seq_num, key_frame_packet.frame_id, false);

	const bool gap = Bool<0>();

	if (gap) {
	// Lose one packet.
	packet_stream.NextPacket();
	}

	auto repeated_packet = packet_stream.NextPacket();
	OnReceivedPacket(repeated_packet);
	if (gap) {
	// Loss notification issued because of the gap. This is not the focus of
	// the test.
	ExpectLossNotification(key_frame_packet.seq_num, repeated_packet.seq_num,
	false);
	}
	OnReceivedPacket(repeated_packet);
	}

	TEST_F(LossNotificationControllerTest,
	RecognizesDependencyAcrossIntraFrameThatIsNotAKeyframe) {
	int last_seq_num = 1;
	auto receive = [&](bool is_key_frame, int64_t frame_id,
	std::vector<int64_t> ref_frame_ids) {
	++last_seq_num;
	OnReceivedPacket(CreatePacket(
	/first_in_frame=/true, /last_in_frame=/true, last_seq_num, frame_id,
	is_key_frame, std::move(ref_frame_ids)));
	OnAssembledFrame(last_seq_num, frame_id, /discardable=/false);
	};
	// 11 -- 13
	// \| \|
	// 10 12
	receive(/is_key_frame=/true, /frame_id=/10, /ref_frame_ids=/{});
	receive(/is_key_frame=/false, /frame_id=/11, /ref_frame_ids=/{10});
	receive(/is_key_frame=/false, /frame_id=/12, /ref_frame_ids=/{});
	receive(/is_key_frame=/false, /frame_id=/13, /ref_frame_ids=/{11, 12});
	EXPECT_FALSE(LastLossNotification());
	}

	class LossNotificationControllerTestDecodabilityFlag
	: public LossNotificationControllerBaseTest {
	protected:
	LossNotificationControllerTestDecodabilityFlag()
	: key_frame_seq_num_(100),
	key_frame_frame_id_(0),
	never_received_frame_id_(key_frame_frame_id_ + 1),
	seq_num_(0),
	frame_id_(0) {}

	void ReceiveKeyFrame() {
	RTC_DCHECK_NE(key_frame_frame_id_, never_received_frame_id_);
	OnReceivedPacket(CreatePacket(true, true, key_frame_seq_num_,
	key_frame_frame_id_, true));
	OnAssembledFrame(key_frame_seq_num_, key_frame_frame_id_, false);
	seq_num_ = key_frame_seq_num_;
	frame_id_ = key_frame_frame_id_;
	}

	void ReceivePacket(bool first_packet_in_frame,
	bool last_packet_in_frame,
	const std::vector<int64_t>& ref_frame_ids) {
	if (first_packet_in_frame) {
	frame_id_ += 1;
	}
	RTC_DCHECK_NE(frame_id_, never_received_frame_id_);
	constexpr bool is_key_frame = false;
	OnReceivedPacket(CreatePacket(first_packet_in_frame, last_packet_in_frame,
	++seq_num_, frame_id_, is_key_frame,
	ref_frame_ids));
	}

	void CreateGap() {
	seq_num_ += 50;
	frame_id_ += 10;
	}

	const uint16_t key_frame_seq_num_;
	const uint16_t key_frame_frame_id_;

	// The tests intentionally never receive this, and can therefore always
	// use this as an unsatisfied dependency.
	const int64_t never_received_frame_id_ = 123;

	uint16_t seq_num_;
	int64_t frame_id_;
	};

	TEST_F(LossNotificationControllerTestDecodabilityFlag,
	SinglePacketFrameWithDecodableDependencies) {
	ReceiveKeyFrame();
	CreateGap();

	const std::vector<int64_t> ref_frame_ids = {key_frame_frame_id_};
	ReceivePacket(true, true, ref_frame_ids);

	const bool expected_decodability_flag = true;
	ExpectLossNotification(key_frame_seq_num_, seq_num_,
	expected_decodability_flag);
	}

	TEST_F(LossNotificationControllerTestDecodabilityFlag,
	SinglePacketFrameWithUndecodableDependencies) {
	ReceiveKeyFrame();
	CreateGap();

	const std::vector<int64_t> ref_frame_ids = {never_received_frame_id_};
	ReceivePacket(true, true, ref_frame_ids);

	const bool expected_decodability_flag = false;
	ExpectLossNotification(key_frame_seq_num_, seq_num_,
	expected_decodability_flag);
	}

	TEST_F(LossNotificationControllerTestDecodabilityFlag,
	FirstPacketOfMultiPacketFrameWithDecodableDependencies) {
	ReceiveKeyFrame();
	CreateGap();

	const std::vector<int64_t> ref_frame_ids = {key_frame_frame_id_};
	ReceivePacket(true, false, ref_frame_ids);

	const bool expected_decodability_flag = true;
	ExpectLossNotification(key_frame_seq_num_, seq_num_,
	expected_decodability_flag);
	}

	TEST_F(LossNotificationControllerTestDecodabilityFlag,
	FirstPacketOfMultiPacketFrameWithUndecodableDependencies) {
	ReceiveKeyFrame();
	CreateGap();

	const std::vector<int64_t> ref_frame_ids = {never_received_frame_id_};
	ReceivePacket(true, false, ref_frame_ids);

	const bool expected_decodability_flag = false;
	ExpectLossNotification(key_frame_seq_num_, seq_num_,
	expected_decodability_flag);
	}

	TEST_F(LossNotificationControllerTestDecodabilityFlag,
	MiddlePacketOfMultiPacketFrameWithDecodableDependenciesIfFirstMissed) {
	ReceiveKeyFrame();
	CreateGap();

	const std::vector<int64_t> ref_frame_ids = {key_frame_frame_id_};
	ReceivePacket(false, false, ref_frame_ids);

	const bool expected_decodability_flag = false;
	ExpectLossNotification(key_frame_seq_num_, seq_num_,
	expected_decodability_flag);
	}

	TEST_F(LossNotificationControllerTestDecodabilityFlag,
	MiddlePacketOfMultiPacketFrameWithUndecodableDependenciesIfFirstMissed) {
	ReceiveKeyFrame();
	CreateGap();

	const std::vector<int64_t> ref_frame_ids = {never_received_frame_id_};
	ReceivePacket(false, false, ref_frame_ids);

	const bool expected_decodability_flag = false;
	ExpectLossNotification(key_frame_seq_num_, seq_num_,
	expected_decodability_flag);
	}

	TEST_F(LossNotificationControllerTestDecodabilityFlag,
	MiddlePacketOfMultiPacketFrameWithDecodableDependenciesIfFirstReceived) {
	ReceiveKeyFrame();
	CreateGap();

	// First packet in multi-packet frame. A loss notification is produced
	// because of the gap in RTP sequence numbers.
	const std::vector<int64_t> ref_frame_ids = {key_frame_frame_id_};
	ReceivePacket(true, false, ref_frame_ids);
	const bool expected_decodability_flag_first = true;
	ExpectLossNotification(key_frame_seq_num_, seq_num_,
	expected_decodability_flag_first);

	// Middle packet in multi-packet frame. No additional gap and the frame is
	// still potentially decodable, so no additional loss indication.
	ReceivePacket(false, false, ref_frame_ids);
	EXPECT_FALSE(LastKeyFrameRequest());
	EXPECT_FALSE(LastLossNotification());
	}

	TEST_F(
	LossNotificationControllerTestDecodabilityFlag,
	MiddlePacketOfMultiPacketFrameWithUndecodableDependenciesIfFirstReceived) {
	ReceiveKeyFrame();
	CreateGap();

	// First packet in multi-packet frame. A loss notification is produced
	// because of the gap in RTP sequence numbers. The frame is also recognized
	// as having non-decodable dependencies.
	const std::vector<int64_t> ref_frame_ids = {never_received_frame_id_};
	ReceivePacket(true, false, ref_frame_ids);
	const bool expected_decodability_flag_first = false;
	ExpectLossNotification(key_frame_seq_num_, seq_num_,
	expected_decodability_flag_first);

	// Middle packet in multi-packet frame. No additional gap, but the frame is
	// known to be non-decodable, so we keep issuing loss indications.
	ReceivePacket(false, false, ref_frame_ids);
	const bool expected_decodability_flag_middle = false;
	ExpectLossNotification(key_frame_seq_num_, seq_num_,
	expected_decodability_flag_middle);
	}

	TEST_F(LossNotificationControllerTestDecodabilityFlag,
	LastPacketOfMultiPacketFrameWithDecodableDependenciesIfAllPrevMissed) {
	ReceiveKeyFrame();
	CreateGap();

	const std::vector<int64_t> ref_frame_ids = {key_frame_frame_id_};
	ReceivePacket(false, true, ref_frame_ids);

	const bool expected_decodability_flag = false;
	ExpectLossNotification(key_frame_seq_num_, seq_num_,
	expected_decodability_flag);
	}

	TEST_F(LossNotificationControllerTestDecodabilityFlag,
	LastPacketOfMultiPacketFrameWithUndecodableDependenciesIfAllPrevMissed) {
	ReceiveKeyFrame();
	CreateGap();

	const std::vector<int64_t> ref_frame_ids = {never_received_frame_id_};
	ReceivePacket(false, true, ref_frame_ids);

	const bool expected_decodability_flag = false;
	ExpectLossNotification(key_frame_seq_num_, seq_num_,
	expected_decodability_flag);
	}

	TEST_F(LossNotificationControllerTestDecodabilityFlag,
	LastPacketOfMultiPacketFrameWithDecodableDependenciesIfAllPrevReceived) {
	ReceiveKeyFrame();
	CreateGap();

	// First packet in multi-packet frame. A loss notification is produced
	// because of the gap in RTP sequence numbers.
	const std::vector<int64_t> ref_frame_ids = {key_frame_frame_id_};
	ReceivePacket(true, false, ref_frame_ids);
	const bool expected_decodability_flag_first = true;
	ExpectLossNotification(key_frame_seq_num_, seq_num_,
	expected_decodability_flag_first);

	// Last packet in multi-packet frame. No additional gap and the frame is
	// still potentially decodable, so no additional loss indication.
	ReceivePacket(false, true, ref_frame_ids);
	EXPECT_FALSE(LastKeyFrameRequest());
	EXPECT_FALSE(LastLossNotification());
	}

	TEST_F(
	LossNotificationControllerTestDecodabilityFlag,
	LastPacketOfMultiPacketFrameWithUndecodableDependenciesIfAllPrevReceived) {
	ReceiveKeyFrame();
	CreateGap();

	// First packet in multi-packet frame. A loss notification is produced
	// because of the gap in RTP sequence numbers. The frame is also recognized
	// as having non-decodable dependencies.
	const std::vector<int64_t> ref_frame_ids = {never_received_frame_id_};
	ReceivePacket(true, false, ref_frame_ids);
	const bool expected_decodability_flag_first = false;
	ExpectLossNotification(key_frame_seq_num_, seq_num_,
	expected_decodability_flag_first);

	// Last packet in multi-packet frame. No additional gap, but the frame is
	// known to be non-decodable, so we keep issuing loss indications.
	ReceivePacket(false, true, ref_frame_ids);
	const bool expected_decodability_flag_last = false;
	ExpectLossNotification(key_frame_seq_num_, seq_num_,
	expected_decodability_flag_last);
	}

	} // namespace webrtc