Add a FlexfecReceiver class.

webrtc/modules/rtp_rtcp/source/flexfec_receiver_unittest.cc

+/*
+ *  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.
+ */
+
+#include <algorithm>
+#include <memory>
+
+#include "webrtc/base/basictypes.h"
+#include "webrtc/modules/rtp_rtcp/include/flexfec_receiver.h"
+#include "webrtc/modules/rtp_rtcp/mocks/mock_recovered_packet_receiver.h"
+#include "webrtc/modules/rtp_rtcp/source/fec_test_helper.h"
+#include "webrtc/modules/rtp_rtcp/source/forward_error_correction.h"
+#include "webrtc/test/gmock.h"
+#include "webrtc/test/gtest.h"
+
+namespace webrtc {
+
+namespace {
+
+using ::testing::_;
+using ::testing::Args;
+using ::testing::ElementsAreArray;
+using ::testing::Return;
+
+using test::fec::FlexfecPacketGenerator;
+using Packet = ForwardErrorCorrection::Packet;
+using PacketList = ForwardErrorCorrection::PacketList;
+
+constexpr size_t kPayloadLength = 500;
+constexpr uint32_t kFlexfecSsrc = 42984;
+constexpr uint32_t kMediaSsrc = 8353;
+
+}  // namespace
+
+class FlexfecReceiverTest : public ::testing::Test {
+ protected:
+  FlexfecReceiverTest()
+      : receiver_(FlexfecReceiver::Create(kFlexfecSsrc,
+                                          kMediaSsrc,
+                                          &recovered_packet_receiver_)),
+        erasure_code_(ForwardErrorCorrection::CreateFlexfec()),
+        packet_generator_(kMediaSsrc, kFlexfecSsrc) {}
+
+  // Generates |num_media_packets| corresponding to a single frame.
+  void PacketizeFrame(size_t num_media_packets,
+                      size_t frame_offset,
+                      PacketList* media_packets);
+
+  // Generates |num_fec_packets| FEC packets, given |media_packets|.
+  std::list<Packet*> EncodeFec(const PacketList& media_packets,
+                               size_t num_fec_packets);
+
+  std::unique_ptr<FlexfecReceiver> receiver_;
+  std::unique_ptr<ForwardErrorCorrection> erasure_code_;
+
+  FlexfecPacketGenerator packet_generator_;
+  testing::StrictMock<MockRecoveredPacketReceiver> recovered_packet_receiver_;
+};
+
+void FlexfecReceiverTest::PacketizeFrame(size_t num_media_packets,
+                                         size_t frame_offset,
+                                         PacketList* media_packets) {
+  packet_generator_.NewFrame(num_media_packets);
+  for (size_t i = 0; i < num_media_packets; ++i) {
+    std::unique_ptr<Packet> next_packet(
+        packet_generator_.NextPacket(frame_offset + i, kPayloadLength));
+    media_packets->push_back(std::move(next_packet));
+  }
+}
+
+std::list<Packet*> FlexfecReceiverTest::EncodeFec(
+    const PacketList& media_packets,
+    size_t num_fec_packets) {
+  const uint8_t protection_factor =
+      num_fec_packets * 255 / media_packets.size();
+  constexpr int kNumImportantPackets = 0;
+  constexpr bool kUseUnequalProtection = false;
+  constexpr FecMaskType kFecMaskType = kFecMaskRandom;
+  std::list<Packet*> fec_packets;
+  EXPECT_EQ(0, erasure_code_->EncodeFec(
+                   media_packets, protection_factor, kNumImportantPackets,
+                   kUseUnequalProtection, kFecMaskType, &fec_packets));
+  EXPECT_EQ(num_fec_packets, fec_packets.size());
+  return fec_packets;
+}
+
+TEST_F(FlexfecReceiverTest, ReceivesMediaPacket) {
+  packet_generator_.NewFrame(1);
+  std::unique_ptr<Packet> media_packet(
+      packet_generator_.NextPacket(0, kPayloadLength));
+
+  EXPECT_EQ(true, receiver_->AddReceivedPacket(media_packet->data,

[danilchap, 2016/10/05 14:32:04]

s/EXPECT_EQ(true,/EXPECT_TRUE(/g

[brandtr, 2016/10/06 08:38:57]

Done.

+                                               media_packet->length));
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+}
+
+TEST_F(FlexfecReceiverTest, FailsOnTruncatedMediaPacket) {
+  const size_t kNoPayload = 0;
+
+  packet_generator_.NewFrame(1);
+  std::unique_ptr<Packet> media_packet(
+      packet_generator_.NextPacket(0, kNoPayload));
+  // Simulate truncated media packet.
+  media_packet->length = kRtpHeaderSize - 1;
+
+  EXPECT_EQ(false, receiver_->AddReceivedPacket(media_packet->data,

[danilchap, 2016/10/05 14:32:04]

EXPECT_FALSE(

[brandtr, 2016/10/06 08:38:57]

Done.

+                                                media_packet->length));
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+}
+
+TEST_F(FlexfecReceiverTest, ReceivesFecPacket) {
+  const size_t kNumMediaPackets = 1;
+  const size_t kNumFecPackets = 1;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPackets, 0, &media_packets);
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+  auto media_packet = media_packets.front().get();
+  auto fec_packet = packet_generator_.BuildFlexfecPacket(*fec_packets.front());
+
+  EXPECT_EQ(true, receiver_->AddReceivedPacket(media_packet->data,
+                                               media_packet->length));
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+  EXPECT_EQ(true,
+            receiver_->AddReceivedPacket(fec_packet->data, fec_packet->length));
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+}
+
+TEST_F(FlexfecReceiverTest, FailsOnTruncatedFecPacket) {
+  const size_t kNumMediaPackets = 1;
+  const size_t kNumFecPackets = 1;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPackets, 0, &media_packets);
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+  auto media_packet = media_packets.front().get();
+  // Simulate truncated FlexFEC payload.
+  fec_packets.front()->length = 1;
+  auto fec_packet = packet_generator_.BuildFlexfecPacket(*fec_packets.front());
+
+  EXPECT_EQ(true, receiver_->AddReceivedPacket(media_packet->data,
+                                               media_packet->length));
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+  EXPECT_EQ(false,
+            receiver_->AddReceivedPacket(fec_packet->data, fec_packet->length));
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+}
+
+TEST_F(FlexfecReceiverTest, FailsOnUnknownMediaSsrc) {
+  const size_t kNumMediaPackets = 1;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPackets, 0, &media_packets);
+  auto media_packet = media_packets.front().get();
+  // Corrupt the SSRC.
+  media_packet->data[8] = 0;
+  media_packet->data[9] = 1;
+  media_packet->data[10] = 2;
+  media_packet->data[11] = 3;
+
+  EXPECT_EQ(false, receiver_->AddReceivedPacket(media_packet->data,
+                                                media_packet->length));
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+}
+
+TEST_F(FlexfecReceiverTest, FailsOnUnknownFecSsrc) {
+  const size_t kNumMediaPackets = 1;
+  const size_t kNumFecPackets = 1;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPackets, 0, &media_packets);
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+  auto media_packet = media_packets.front().get();
+  auto fec_packet = packet_generator_.BuildFlexfecPacket(*fec_packets.front());
+  // Corrupt the SSRC.
+  fec_packet->data[8] = 4;
+  fec_packet->data[9] = 5;
+  fec_packet->data[10] = 6;
+  fec_packet->data[11] = 7;
+
+  EXPECT_EQ(true, receiver_->AddReceivedPacket(media_packet->data,
+                                               media_packet->length));
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+  EXPECT_EQ(false,
+            receiver_->AddReceivedPacket(fec_packet->data, fec_packet->length));
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+}
+
+TEST_F(FlexfecReceiverTest, ReceivesMultiplePackets) {
+  const size_t kNumMediaPackets = 2;
+  const size_t kNumFecPackets = 1;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPackets, 0, &media_packets);
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+
+  // Receive all media packets.
+  for (const auto& media_packet : media_packets) {
+    EXPECT_EQ(true, receiver_->AddReceivedPacket(media_packet->data,
+                                                 media_packet->length));
+    EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+  }
+
+  // Receive FEC packet.
+  auto fec_it = fec_packets.begin();
+  std::unique_ptr<Packet> packet_with_rtp_header =
+      packet_generator_.BuildFlexfecPacket(**fec_it);
+  EXPECT_EQ(true, receiver_->AddReceivedPacket(packet_with_rtp_header->data,
+                                               packet_with_rtp_header->length));
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+}
+
+TEST_F(FlexfecReceiverTest, RecoversFromSingleMediaLoss) {
+  const size_t kNumMediaPackets = 2;
+  const size_t kNumFecPackets = 1;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPackets, 0, &media_packets);
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+
+  // Receive first media packet but drop second.
+  auto media_it = media_packets.begin();
+  EXPECT_EQ(true, receiver_->AddReceivedPacket((*media_it)->data,
+                                               (*media_it)->length));
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+
+  // Receive FEC packet.
+  auto fec_it = fec_packets.begin();
+  std::unique_ptr<Packet> packet_with_rtp_header =
+      packet_generator_.BuildFlexfecPacket(**fec_it);
+  EXPECT_EQ(true, receiver_->AddReceivedPacket(packet_with_rtp_header->data,
+                                               packet_with_rtp_header->length));
+
+  // Ensure recovery of lost media packet.
+  media_it++;
+  EXPECT_CALL(recovered_packet_receiver_,
+              OnRecoveredPacket(_, (*media_it)->length))
+      .With(
+          Args<0, 1>(ElementsAreArray((*media_it)->data, (*media_it)->length)))
+      .WillOnce(Return(true));
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+}
+
+TEST_F(FlexfecReceiverTest, RecoversFromDoubleMediaLoss) {
+  const size_t kNumMediaPackets = 2;
+  const size_t kNumFecPackets = 2;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPackets, 0, &media_packets);
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+
+  // Drop both media packets.
+  auto media_it = media_packets.begin();
+
+  // Receive first FEC packet.
+  auto fec_it = fec_packets.begin();
+  std::unique_ptr<Packet> packet_with_rtp_header =
+      packet_generator_.BuildFlexfecPacket(**fec_it);
+  EXPECT_EQ(true, receiver_->AddReceivedPacket(packet_with_rtp_header->data,
+                                               packet_with_rtp_header->length));
+
+  // Recover first lost media packet.
+  EXPECT_CALL(recovered_packet_receiver_,
+              OnRecoveredPacket(_, (*media_it)->length))
+      .With(
+          Args<0, 1>(ElementsAreArray((*media_it)->data, (*media_it)->length)))
+      .WillOnce(Return(true));
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+
+  // Receive second FEC packet.
+  fec_it++;
+  packet_with_rtp_header = packet_generator_.BuildFlexfecPacket(**fec_it);
+  EXPECT_EQ(true, receiver_->AddReceivedPacket(packet_with_rtp_header->data,
+                                               packet_with_rtp_header->length));
+
+  // Recover second lost media packet.
+  media_it++;
+  EXPECT_CALL(recovered_packet_receiver_,
+              OnRecoveredPacket(_, (*media_it)->length))
+      .With(
+          Args<0, 1>(ElementsAreArray((*media_it)->data, (*media_it)->length)))
+      .WillOnce(Return(true));
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+}
+
+TEST_F(FlexfecReceiverTest, DoesNotRecoverFromMediaAndFecLoss) {
+  const size_t kNumMediaPackets = 2;
+  const size_t kNumFecPackets = 1;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPackets, 0, &media_packets);
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+
+  // Receive first media packet.
+  auto media_it = media_packets.begin();
+  EXPECT_EQ(true, receiver_->AddReceivedPacket((*media_it)->data,
+                                               (*media_it)->length));
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+
+  // Drop second media packet and FEC packet.
+}
+
+TEST_F(FlexfecReceiverTest, DoesNotCallbackTwice) {
+  const size_t kNumMediaPackets = 2;
+  const size_t kNumFecPackets = 1;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPackets, 0, &media_packets);
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+
+  // Receive first media packet but drop second.
+  auto media_it = media_packets.begin();
+  EXPECT_EQ(true, receiver_->AddReceivedPacket((*media_it)->data,
+                                               (*media_it)->length));
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+
+  // Receive FEC packet.
+  auto fec_it = fec_packets.begin();
+  std::unique_ptr<Packet> packet_with_rtp_header =
+      packet_generator_.BuildFlexfecPacket(**fec_it);
+  EXPECT_EQ(true, receiver_->AddReceivedPacket(packet_with_rtp_header->data,
+                                               packet_with_rtp_header->length));
+
+  // Ensure recovery of lost media packet.
+  media_it++;
+  EXPECT_CALL(recovered_packet_receiver_,
+              OnRecoveredPacket(_, (*media_it)->length))
+      .With(
+          Args<0, 1>(ElementsAreArray((*media_it)->data, (*media_it)->length)))
+      .WillOnce(Return(true));
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+
+  // Receive FEC packet again.
+  EXPECT_EQ(true, receiver_->AddReceivedPacket(packet_with_rtp_header->data,
+                                               packet_with_rtp_header->length));
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+}
+
+// Here we are implicitly assuming packet masks that are suitable for
+// this type of 50% correlated loss. If we are changing our precomputed
+// packet masks, this test might need to be updated.
+TEST_F(FlexfecReceiverTest, RecoversFrom50PercentLoss) {
+  const size_t kNumFecPackets = 5;
+  const size_t kNumFrames = 2 * kNumFecPackets;
+  const size_t kNumMediaPacketsPerFrame = 1;
+
+  PacketList media_packets;
+  for (size_t i = 0; i < kNumFrames; ++i) {
+    PacketizeFrame(kNumMediaPacketsPerFrame, i, &media_packets);
+  }
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+
+  // Drop every second media packet.
+  auto media_it = media_packets.begin();
+  while (media_it != media_packets.end()) {
+    EXPECT_EQ(true, receiver_->AddReceivedPacket((*media_it)->data,
+                                                 (*media_it)->length));
+    EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+    ++media_it;
+    if (media_it == media_packets.end()) {
+      break;
+    }
+    ++media_it;
+  }
+
+  // Receive all FEC packets.
+  media_it = media_packets.begin();
+  for (const auto& fec_packet : fec_packets) {
+    std::unique_ptr<Packet> fec_packet_with_rtp_header =
+        packet_generator_.BuildFlexfecPacket(*fec_packet);
+    EXPECT_EQ(true,
+              receiver_->AddReceivedPacket(fec_packet_with_rtp_header->data,
+                                           fec_packet_with_rtp_header->length));
+    ++media_it;
+    if (media_it == media_packets.end()) {
+      break;
+    }
+    EXPECT_CALL(recovered_packet_receiver_,
+                OnRecoveredPacket(_, (*media_it)->length))
+        .With(Args<0, 1>(
+            ElementsAreArray((*media_it)->data, (*media_it)->length)))
+        .WillOnce(Return(true));
+    ++media_it;
+    EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+  }
+}
+
+TEST_F(FlexfecReceiverTest, DelayedFecPacketDoesHelp) {
+  // These values need to be updated if the underlying erasure code
+  // implementation changes.
+  const size_t kNumFrames = 48;
+  const size_t kNumMediaPacketsPerFrame = 1;
+  const size_t kNumFecPackets = 1;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPacketsPerFrame, 0, &media_packets);
+  PacketizeFrame(kNumMediaPacketsPerFrame, 1, &media_packets);
+  // Protect two first frames.
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+  for (size_t i = 2; i < kNumFrames; ++i) {
+    PacketizeFrame(kNumMediaPacketsPerFrame, i, &media_packets);
+  }
+
+  // Drop first media packet and delay FEC packet.
+  auto media_it = media_packets.begin();
+  ++media_it;
+
+  // Receive all other media packets.
+  while (media_it != media_packets.end()) {
+    EXPECT_EQ(true, receiver_->AddReceivedPacket((*media_it)->data,
+                                                 (*media_it)->length));
+    EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+    ++media_it;
+  }
+
+  // Receive FEC packet.
+  auto fec_it = fec_packets.begin();
+  std::unique_ptr<Packet> packet_with_rtp_header =
+      packet_generator_.BuildFlexfecPacket(**fec_it);
+  EXPECT_EQ(true, receiver_->AddReceivedPacket(packet_with_rtp_header->data,
+                                               packet_with_rtp_header->length));
+
+  // Recover first media packet.
+  media_it = media_packets.begin();
+  EXPECT_CALL(recovered_packet_receiver_,
+              OnRecoveredPacket(_, (*media_it)->length))
+      .With(
+          Args<0, 1>(ElementsAreArray((*media_it)->data, (*media_it)->length)))
+      .WillOnce(Return(true));
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+}
+
+TEST_F(FlexfecReceiverTest, TooDelayedFecPacketDoesNotHelp) {
+  // These values need to be updated if the underlying erasure code
+  // implementation changes.
+  const size_t kNumFrames = 49;
+  const size_t kNumMediaPacketsPerFrame = 1;
+  const size_t kNumFecPackets = 1;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPacketsPerFrame, 0, &media_packets);
+  PacketizeFrame(kNumMediaPacketsPerFrame, 1, &media_packets);
+  // Protect two first frames.
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+  for (size_t i = 2; i < kNumFrames; ++i) {
+    PacketizeFrame(kNumMediaPacketsPerFrame, i, &media_packets);
+  }
+
+  // Drop first media packet and delay FEC packet.
+  auto media_it = media_packets.begin();
+  ++media_it;
+
+  // Receive all other media packets.
+  while (media_it != media_packets.end()) {
+    EXPECT_EQ(true, receiver_->AddReceivedPacket((*media_it)->data,
+                                                 (*media_it)->length));
+    EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+    ++media_it;
+  }
+
+  // Receive FEC packet.
+  auto fec_it = fec_packets.begin();
+  std::unique_ptr<Packet> packet_with_rtp_header =
+      packet_generator_.BuildFlexfecPacket(**fec_it);
+  EXPECT_EQ(true, receiver_->AddReceivedPacket(packet_with_rtp_header->data,
+                                               packet_with_rtp_header->length));
+  // Do not expect a callback.
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+}
+
+TEST_F(FlexfecReceiverTest, RecoversWithMediaPacketsOutOfOrder) {
+  const size_t kNumMediaPackets = 6;
+  const size_t kNumFecPackets = 2;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPackets, 0, &media_packets);
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+
+  // Lose two media packets, and receive the others out of order.
+  auto media_it = media_packets.begin();
+  auto media_packet0 = media_it++;
+  auto media_packet1 = media_it++;
+  auto media_packet2 = media_it++;
+  auto media_packet3 = media_it++;
+  auto media_packet4 = media_it++;
+  auto media_packet5 = media_it++;
+  EXPECT_EQ(true, receiver_->AddReceivedPacket((*media_packet5)->data,
+                                               (*media_packet5)->length));
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+  EXPECT_EQ(true, receiver_->AddReceivedPacket((*media_packet2)->data,
+                                               (*media_packet2)->length));
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+  EXPECT_EQ(true, receiver_->AddReceivedPacket((*media_packet3)->data,
+                                               (*media_packet3)->length));
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+  EXPECT_EQ(true, receiver_->AddReceivedPacket((*media_packet0)->data,
+                                               (*media_packet0)->length));
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+
+  // Add FEC packets.
+  auto fec_it = fec_packets.begin();
+  std::unique_ptr<Packet> packet_with_rtp_header;
+  while (fec_it != fec_packets.end()) {
+    packet_with_rtp_header = packet_generator_.BuildFlexfecPacket(**fec_it);
+    EXPECT_EQ(true,
+              receiver_->AddReceivedPacket(packet_with_rtp_header->data,
+                                           packet_with_rtp_header->length));
+    ++fec_it;
+  }
+
+  // Recover lost media packets.
+  EXPECT_CALL(recovered_packet_receiver_,
+              OnRecoveredPacket(_, (*media_packet1)->length))
+      .With(Args<0, 1>(
+          ElementsAreArray((*media_packet1)->data, (*media_packet1)->length)))
+      .WillOnce(Return(true));
+  EXPECT_CALL(recovered_packet_receiver_,
+              OnRecoveredPacket(_, (*media_packet4)->length))
+      .With(Args<0, 1>(
+          ElementsAreArray((*media_packet4)->data, (*media_packet4)->length)))
+      .WillOnce(Return(true));
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+}
+
+TEST_F(FlexfecReceiverTest, CalculatesNumberOfPackets) {
+  const size_t kNumMediaPackets = 2;
+  const size_t kNumFecPackets = 1;
+
+  PacketList media_packets;
+  PacketizeFrame(kNumMediaPackets, 0, &media_packets);
+  std::list<Packet*> fec_packets = EncodeFec(media_packets, kNumFecPackets);
+
+  // Receive first media packet but drop second.
+  auto media_it = media_packets.begin();
+  EXPECT_EQ(true, receiver_->AddReceivedPacket((*media_it)->data,
+                                               (*media_it)->length));
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+
+  // Receive FEC packet.
+  auto fec_it = fec_packets.begin();
+  std::unique_ptr<Packet> packet_with_rtp_header =
+      packet_generator_.BuildFlexfecPacket(**fec_it);
+  EXPECT_EQ(true, receiver_->AddReceivedPacket(packet_with_rtp_header->data,
+                                               packet_with_rtp_header->length));
+
+  // Ensure recovery of lost media packet.
+  media_it++;
+  EXPECT_CALL(recovered_packet_receiver_,
+              OnRecoveredPacket(_, (*media_it)->length))
+      .With(
+          Args<0, 1>(ElementsAreArray((*media_it)->data, (*media_it)->length)))
+      .WillOnce(Return(true));
+  EXPECT_EQ(true, receiver_->ProcessReceivedPackets());
+
+  // Check stats calculations.
+  auto packet_counter = receiver_->GetPacketCounter();
+  EXPECT_EQ(2U, packet_counter.num_packets);
+  EXPECT_EQ(1U, packet_counter.num_fec_packets);
+  EXPECT_EQ(1U, packet_counter.num_recovered_packets);
+}
+
+}  // namespace webrtc