src/third_party/webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_unittest_helper.cc

   1 /*
   2  *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
   3  *
   4  *  Use of this source code is governed by a BSD-style license
   5  *  that can be found in the LICENSE file in the root of the source
   6  *  tree. An additional intellectual property rights grant can be found
   7  *  in the file PATENTS.  All contributing project authors may
   8  *  be found in the AUTHORS file in the root of the source tree.
   9  */
  10 #include "webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_unittest_helper.h"
  11
  12 #include <algorithm>
  13 #include <utility>
  14
  15 namespace webrtc {
  16
  17 enum { kMtu = 1200, kAcceptedBitrateErrorBps = 50000u };
  18
  19 namespace testing {
  20
  21 void TestBitrateObserver::OnReceiveBitrateChanged(
  22     const std::vector<unsigned int>& ssrcs,
  23     unsigned int bitrate) {
  24   latest_bitrate_ = bitrate;
  25   updated_ = true;
  26 }
  27
  28 RtpStream::RtpStream(int fps,
  29                      int bitrate_bps,
  30                      unsigned int ssrc,
  31                      unsigned int frequency,
  32                      uint32_t timestamp_offset,
  33                      int64_t rtcp_receive_time)
  34     : fps_(fps),
  35       bitrate_bps_(bitrate_bps),
  36       ssrc_(ssrc),
  37       frequency_(frequency),
  38       next_rtp_time_(0),
  39       next_rtcp_time_(rtcp_receive_time),
  40       rtp_timestamp_offset_(timestamp_offset),
  41       kNtpFracPerMs(4.294967296E6) {
  42   assert(fps_ > 0);
  43 }
  44
  45 void RtpStream::set_rtp_timestamp_offset(uint32_t offset) {
  46   rtp_timestamp_offset_ = offset;
  47 }
  48
  49 // Generates a new frame for this stream. If called too soon after the
  50 // previous frame, no frame will be generated. The frame is split into
  51 // packets.
  52 int64_t RtpStream::GenerateFrame(int64_t time_now_us, PacketList* packets) {
  53   if (time_now_us < next_rtp_time_) {
  54     return next_rtp_time_;
  55   }
  56   assert(packets != NULL);
  57   int bits_per_frame = (bitrate_bps_ + fps_ / 2) / fps_;
  58   int n_packets = std::max((bits_per_frame + 4 * kMtu) / (8 * kMtu), 1);
  59   int packet_size = (bits_per_frame + 4 * n_packets) / (8 * n_packets);
  60   assert(n_packets >= 0);
  61   for (int i = 0; i < n_packets; ++i) {
  62     RtpPacket* packet = new RtpPacket;
  63     packet->send_time = time_now_us + kSendSideOffsetUs;
  64     packet->size = packet_size;
  65     packet->rtp_timestamp = rtp_timestamp_offset_ + static_cast<uint32_t>(
  66         ((frequency_ / 1000) * packet->send_time + 500) / 1000);
  67     packet->ssrc = ssrc_;
  68     packets->push_back(packet);
  69   }
  70   next_rtp_time_ = time_now_us + (1000000 + fps_ / 2) / fps_;
  71   return next_rtp_time_;
  72 }
  73
  74 // The send-side time when the next frame can be generated.
  75 double RtpStream::next_rtp_time() const {
  76   return next_rtp_time_;
  77 }
  78
  79 // Generates an RTCP packet.
  80 RtpStream::RtcpPacket* RtpStream::Rtcp(int64_t time_now_us) {
  81   if (time_now_us < next_rtcp_time_) {
  82     return NULL;
  83   }
  84   RtcpPacket* rtcp = new RtcpPacket;
  85   int64_t send_time_us = time_now_us + kSendSideOffsetUs;
  86   rtcp->timestamp = rtp_timestamp_offset_ + static_cast<uint32_t>(
  87       ((frequency_ / 1000) * send_time_us + 500) / 1000);
  88   rtcp->ntp_secs = send_time_us / 1000000;
  89   rtcp->ntp_frac = static_cast<int64_t>((send_time_us % 1000000) *
  90       kNtpFracPerMs);
  91   rtcp->ssrc = ssrc_;
  92   next_rtcp_time_ = time_now_us + kRtcpIntervalUs;
  93   return rtcp;
  94 }
  95
  96 void RtpStream::set_bitrate_bps(int bitrate_bps) {
  97   ASSERT_GE(bitrate_bps, 0);
  98   bitrate_bps_ = bitrate_bps;
  99 }
 100
 101 int RtpStream::bitrate_bps() const {
 102   return bitrate_bps_;
 103 }
 104
 105 unsigned int RtpStream::ssrc() const {
 106   return ssrc_;
 107 }
 108
 109 bool RtpStream::Compare(const std::pair<unsigned int, RtpStream*>& left,
 110                         const std::pair<unsigned int, RtpStream*>& right) {
 111   return left.second->next_rtp_time_ < right.second->next_rtp_time_;
 112 }
 113
 114 StreamGenerator::StreamGenerator(int capacity, double time_now)
 115     : capacity_(capacity),
 116       prev_arrival_time_us_(time_now) {}
 117
 118 StreamGenerator::~StreamGenerator() {
 119   for (StreamMap::iterator it = streams_.begin(); it != streams_.end();
 120       ++it) {
 121     delete it->second;
 122   }
 123   streams_.clear();
 124 }
 125
 126 // Add a new stream.
 127 void StreamGenerator::AddStream(RtpStream* stream) {
 128   streams_[stream->ssrc()] = stream;
 129 }
 130
 131 // Set the link capacity.
 132 void StreamGenerator::set_capacity_bps(int capacity_bps) {
 133   ASSERT_GT(capacity_bps, 0);
 134   capacity_ = capacity_bps;
 135 }
 136
 137 // Divides |bitrate_bps| among all streams. The allocated bitrate per stream
 138 // is decided by the current allocation ratios.
 139 void StreamGenerator::SetBitrateBps(int bitrate_bps) {
 140   ASSERT_GE(streams_.size(), 0u);
 141   int total_bitrate_before = 0;
 142   for (StreamMap::iterator it = streams_.begin(); it != streams_.end(); ++it) {
 143     total_bitrate_before += it->second->bitrate_bps();
 144   }
 145   int64_t bitrate_before = 0;
 146   int total_bitrate_after = 0;
 147   for (StreamMap::iterator it = streams_.begin(); it != streams_.end(); ++it) {
 148     bitrate_before += it->second->bitrate_bps();
 149     int64_t bitrate_after = (bitrate_before * bitrate_bps +
 150         total_bitrate_before / 2) / total_bitrate_before;
 151     it->second->set_bitrate_bps(bitrate_after - total_bitrate_after);
 152     total_bitrate_after += it->second->bitrate_bps();
 153   }
 154   ASSERT_EQ(bitrate_before, total_bitrate_before);
 155   EXPECT_EQ(total_bitrate_after, bitrate_bps);
 156 }
 157
 158 // Set the RTP timestamp offset for the stream identified by |ssrc|.
 159 void StreamGenerator::set_rtp_timestamp_offset(unsigned int ssrc,
 160                                                uint32_t offset) {
 161   streams_[ssrc]->set_rtp_timestamp_offset(offset);
 162 }
 163
 164 // TODO(holmer): Break out the channel simulation part from this class to make
 165 // it possible to simulate different types of channels.
 166 int64_t StreamGenerator::GenerateFrame(RtpStream::PacketList* packets,
 167                                        int64_t time_now_us) {
 168   assert(packets != NULL);
 169   assert(packets->empty());
 170   assert(capacity_ > 0);
 171   StreamMap::iterator it = std::min_element(streams_.begin(), streams_.end(),
 172                                             RtpStream::Compare);
 173   (*it).second->GenerateFrame(time_now_us, packets);
 174   int i = 0;
 175   for (RtpStream::PacketList::iterator packet_it = packets->begin();
 176       packet_it != packets->end(); ++packet_it) {
 177     int capacity_bpus = capacity_ / 1000;
 178     int64_t required_network_time_us =
 179         (8 * 1000 * (*packet_it)->size + capacity_bpus / 2) / capacity_bpus;
 180     prev_arrival_time_us_ = std::max(time_now_us + required_network_time_us,
 181         prev_arrival_time_us_ + required_network_time_us);
 182     (*packet_it)->arrival_time = prev_arrival_time_us_;
 183     ++i;
 184   }
 185   it = std::min_element(streams_.begin(), streams_.end(), RtpStream::Compare);
 186   return (*it).second->next_rtp_time();
 187 }
 188 }  // namespace testing
 189
 190 RemoteBitrateEstimatorTest::RemoteBitrateEstimatorTest()
 191     : clock_(0),
 192       bitrate_observer_(new testing::TestBitrateObserver),
 193       stream_generator_(new testing::StreamGenerator(
 194           1e6,  // Capacity.
 195           clock_.TimeInMicroseconds())) {}
 196
 197 RemoteBitrateEstimatorTest::~RemoteBitrateEstimatorTest() {}
 198
 199 void RemoteBitrateEstimatorTest::AddDefaultStream() {
 200   stream_generator_->AddStream(new testing::RtpStream(
 201     30,          // Frames per second.
 202     3e5,         // Bitrate.
 203     1,           // SSRC.
 204     90000,       // RTP frequency.
 205     0xFFFFF000,  // Timestamp offset.
 206     0));         // RTCP receive time.
 207 }
 208
 209 uint32_t RemoteBitrateEstimatorTest::AbsSendTime(int64_t t, int64_t denom) {
 210   return (((t << 18) + (denom >> 1)) / denom) & 0x00fffffful;
 211 }
 212
 213 uint32_t RemoteBitrateEstimatorTest::AddAbsSendTime(uint32_t t1, uint32_t t2) {
 214   return (t1 + t2) & 0x00fffffful;
 215 }
 216
 217 const unsigned int RemoteBitrateEstimatorTest::kDefaultSsrc = 1;
 218
 219 void RemoteBitrateEstimatorTest::IncomingPacket(uint32_t ssrc,
 220                                                 uint32_t payload_size,
 221                                                 int64_t arrival_time,
 222                                                 uint32_t rtp_timestamp,
 223                                                 uint32_t absolute_send_time) {
 224   RTPHeader header;
 225   memset(&header, 0, sizeof(header));
 226   header.ssrc = ssrc;
 227   header.timestamp = rtp_timestamp;
 228   header.extension.hasAbsoluteSendTime = true;
 229   header.extension.absoluteSendTime = absolute_send_time;
 230   bitrate_estimator_->IncomingPacket(arrival_time + kArrivalTimeClockOffsetMs,
 231       payload_size, header);
 232 }
 233
 234 // Generates a frame of packets belonging to a stream at a given bitrate and
 235 // with a given ssrc. The stream is pushed through a very simple simulated
 236 // network, and is then given to the receive-side bandwidth estimator.
 237 // Returns true if an over-use was seen, false otherwise.
 238 // The StreamGenerator::updated() should be used to check for any changes in
 239 // target bitrate after the call to this function.
 240 bool RemoteBitrateEstimatorTest::GenerateAndProcessFrame(unsigned int ssrc,
 241     unsigned int bitrate_bps) {
 242   stream_generator_->SetBitrateBps(bitrate_bps);
 243   testing::RtpStream::PacketList packets;
 244   int64_t next_time_us = stream_generator_->GenerateFrame(
 245       &packets, clock_.TimeInMicroseconds());
 246   bool overuse = false;
 247   while (!packets.empty()) {
 248     testing::RtpStream::RtpPacket* packet = packets.front();
 249     bitrate_observer_->Reset();
 250     // The simulated clock should match the time of packet->arrival_time
 251     // since both are used in IncomingPacket().
 252     clock_.AdvanceTimeMicroseconds(packet->arrival_time -
 253                                    clock_.TimeInMicroseconds());
 254     IncomingPacket(packet->ssrc,
 255                    packet->size,
 256                    (packet->arrival_time + 500) / 1000,
 257                    packet->rtp_timestamp,
 258                    AbsSendTime(packet->send_time, 1000000));
 259     if (bitrate_observer_->updated()) {
 260       // Verify that new estimates only are triggered by an overuse and a
 261       // rate decrease.
 262       overuse = true;
 263       EXPECT_LE(bitrate_observer_->latest_bitrate(), bitrate_bps);
 264     }
 265     delete packet;
 266     packets.pop_front();
 267   }
 268   bitrate_estimator_->Process();
 269   clock_.AdvanceTimeMicroseconds(next_time_us - clock_.TimeInMicroseconds());
 270   return overuse;
 271 }
 272
 273 // Run the bandwidth estimator with a stream of |number_of_frames| frames, or
 274 // until it reaches |target_bitrate|.
 275 // Can for instance be used to run the estimator for some time to get it
 276 // into a steady state.
 277 unsigned int RemoteBitrateEstimatorTest::SteadyStateRun(
 278     unsigned int ssrc,
 279     int max_number_of_frames,
 280     unsigned int start_bitrate,
 281     unsigned int min_bitrate,
 282     unsigned int max_bitrate,
 283     unsigned int target_bitrate) {
 284   unsigned int bitrate_bps = start_bitrate;
 285   bool bitrate_update_seen = false;
 286   // Produce |number_of_frames| frames and give them to the estimator.
 287   for (int i = 0; i < max_number_of_frames; ++i) {
 288     bool overuse = GenerateAndProcessFrame(ssrc, bitrate_bps);
 289     if (overuse) {
 290       EXPECT_LT(bitrate_observer_->latest_bitrate(), max_bitrate);
 291       EXPECT_GT(bitrate_observer_->latest_bitrate(), min_bitrate);
 292       bitrate_bps = bitrate_observer_->latest_bitrate();
 293       bitrate_update_seen = true;
 294     } else if (bitrate_observer_->updated()) {
 295       bitrate_bps = bitrate_observer_->latest_bitrate();
 296       bitrate_observer_->Reset();
 297     }
 298     if (bitrate_update_seen && bitrate_bps > target_bitrate) {
 299       break;
 300     }
 301   }
 302   EXPECT_TRUE(bitrate_update_seen);
 303   return bitrate_bps;
 304 }
 305
 306 void RemoteBitrateEstimatorTest::InitialBehaviorTestHelper(
 307     unsigned int expected_converge_bitrate) {
 308   const int kFramerate = 50;  // 50 fps to avoid rounding errors.
 309   const int kFrameIntervalMs = 1000 / kFramerate;
 310   const uint32_t kFrameIntervalAbsSendTime = AbsSendTime(1, kFramerate);
 311   unsigned int bitrate_bps = 0;
 312   uint32_t timestamp = 0;
 313   uint32_t absolute_send_time = 0;
 314   std::vector<unsigned int> ssrcs;
 315   EXPECT_FALSE(bitrate_estimator_->LatestEstimate(&ssrcs, &bitrate_bps));
 316   EXPECT_EQ(0u, ssrcs.size());
 317   clock_.AdvanceTimeMilliseconds(1000);
 318   bitrate_estimator_->Process();
 319   EXPECT_FALSE(bitrate_estimator_->LatestEstimate(&ssrcs, &bitrate_bps));
 320   EXPECT_FALSE(bitrate_observer_->updated());
 321   bitrate_observer_->Reset();
 322   clock_.AdvanceTimeMilliseconds(1000);
 323   // Inserting a packet. Still no valid estimate. We need to wait 1 second.
 324   IncomingPacket(kDefaultSsrc, kMtu, clock_.TimeInMilliseconds(), timestamp,
 325                  absolute_send_time);
 326   bitrate_estimator_->Process();
 327   EXPECT_FALSE(bitrate_estimator_->LatestEstimate(&ssrcs, &bitrate_bps));
 328   EXPECT_EQ(0u, ssrcs.size());
 329   EXPECT_FALSE(bitrate_observer_->updated());
 330   bitrate_observer_->Reset();
 331   // Inserting packets for one second to get a valid estimate.
 332   for (int i = 0; i < kFramerate; ++i) {
 333     IncomingPacket(kDefaultSsrc, kMtu, clock_.TimeInMilliseconds(), timestamp,
 334                    absolute_send_time);
 335     clock_.AdvanceTimeMilliseconds(1000 / kFramerate);
 336     timestamp += 90 * kFrameIntervalMs;
 337     absolute_send_time = AddAbsSendTime(absolute_send_time,
 338                                         kFrameIntervalAbsSendTime);
 339   }
 340   bitrate_estimator_->Process();
 341   EXPECT_TRUE(bitrate_estimator_->LatestEstimate(&ssrcs, &bitrate_bps));
 342   ASSERT_EQ(1u, ssrcs.size());
 343   EXPECT_EQ(kDefaultSsrc, ssrcs.front());
 344   EXPECT_NEAR(expected_converge_bitrate, bitrate_bps, kAcceptedBitrateErrorBps);
 345   EXPECT_TRUE(bitrate_observer_->updated());
 346   bitrate_observer_->Reset();
 347   EXPECT_EQ(bitrate_observer_->latest_bitrate(), bitrate_bps);
 348   bitrate_estimator_->RemoveStream(kDefaultSsrc);
 349   EXPECT_TRUE(bitrate_estimator_->LatestEstimate(&ssrcs, &bitrate_bps));
 350   ASSERT_EQ(0u, ssrcs.size());
 351   EXPECT_EQ(0u, bitrate_bps);
 352 }
 353
 354 void RemoteBitrateEstimatorTest::RateIncreaseReorderingTestHelper(
 355     uint32_t expected_bitrate_bps) {
 356   const int kFramerate = 50;  // 50 fps to avoid rounding errors.
 357   const int kFrameIntervalMs = 1000 / kFramerate;
 358   const uint32_t kFrameIntervalAbsSendTime = AbsSendTime(1, kFramerate);
 359   uint32_t timestamp = 0;
 360   uint32_t absolute_send_time = 0;
 361   IncomingPacket(kDefaultSsrc, 1000, clock_.TimeInMilliseconds(), timestamp,
 362                  absolute_send_time);
 363   bitrate_estimator_->Process();
 364   EXPECT_FALSE(bitrate_observer_->updated());  // No valid estimate.
 365   // Inserting packets for one second to get a valid estimate.
 366   for (int i = 0; i < kFramerate; ++i) {
 367     IncomingPacket(kDefaultSsrc, kMtu, clock_.TimeInMilliseconds(), timestamp,
 368                    absolute_send_time);
 369     clock_.AdvanceTimeMilliseconds(kFrameIntervalMs);
 370     timestamp += 90 * kFrameIntervalMs;
 371     absolute_send_time = AddAbsSendTime(absolute_send_time,
 372                                         kFrameIntervalAbsSendTime);
 373   }
 374   bitrate_estimator_->Process();
 375   EXPECT_TRUE(bitrate_observer_->updated());
 376   EXPECT_NEAR(expected_bitrate_bps,
 377               bitrate_observer_->latest_bitrate(),
 378               kAcceptedBitrateErrorBps);
 379   for (int i = 0; i < 10; ++i) {
 380     clock_.AdvanceTimeMilliseconds(2 * kFrameIntervalMs);
 381     timestamp += 2 * 90 * kFrameIntervalMs;
 382     absolute_send_time = AddAbsSendTime(absolute_send_time,
 383                                         2 * kFrameIntervalAbsSendTime);
 384     IncomingPacket(kDefaultSsrc, 1000, clock_.TimeInMilliseconds(), timestamp,
 385                    absolute_send_time);
 386     IncomingPacket(kDefaultSsrc, 1000, clock_.TimeInMilliseconds(),
 387                    timestamp - 90 * kFrameIntervalMs,
 388                    AddAbsSendTime(absolute_send_time,
 389                                   -int(kFrameIntervalAbsSendTime)));
 390   }
 391   bitrate_estimator_->Process();
 392   EXPECT_TRUE(bitrate_observer_->updated());
 393   EXPECT_NEAR(expected_bitrate_bps,
 394               bitrate_observer_->latest_bitrate(),
 395               kAcceptedBitrateErrorBps);
 396 }
 397
 398 // Make sure we initially increase the bitrate as expected.
 399 void RemoteBitrateEstimatorTest::RateIncreaseRtpTimestampsTestHelper(
 400     int expected_iterations) {
 401   // This threshold corresponds approximately to increasing linearly with
 402   // bitrate(i) = 1.04 * bitrate(i-1) + 1000
 403   // until bitrate(i) > 500000, with bitrate(1) ~= 30000.
 404   unsigned int bitrate_bps = 30000;
 405   int iterations = 0;
 406   AddDefaultStream();
 407   // Feed the estimator with a stream of packets and verify that it reaches
 408   // 500 kbps at the expected time.
 409   while (bitrate_bps < 5e5) {
 410     bool overuse = GenerateAndProcessFrame(kDefaultSsrc, bitrate_bps);
 411     if (overuse) {
 412       EXPECT_GT(bitrate_observer_->latest_bitrate(), bitrate_bps);
 413       bitrate_bps = bitrate_observer_->latest_bitrate();
 414       bitrate_observer_->Reset();
 415     } else if (bitrate_observer_->updated()) {
 416       bitrate_bps = bitrate_observer_->latest_bitrate();
 417       bitrate_observer_->Reset();
 418     }
 419     ++iterations;
 420     ASSERT_LE(iterations, expected_iterations);
 421   }
 422   ASSERT_EQ(expected_iterations, iterations);
 423 }
 424
 425 void RemoteBitrateEstimatorTest::CapacityDropTestHelper(
 426     int number_of_streams,
 427     bool wrap_time_stamp,
 428     unsigned int expected_bitrate_drop_delta) {
 429   const int kFramerate = 30;
 430   const int kStartBitrate = 900e3;
 431   const int kMinExpectedBitrate = 800e3;
 432   const int kMaxExpectedBitrate = 1100e3;
 433   const unsigned int kInitialCapacityBps = 1000e3;
 434   const unsigned int kReducedCapacityBps = 500e3;
 435
 436   int steady_state_time = 0;
 437   if (number_of_streams <= 1) {
 438     steady_state_time = 10;
 439     AddDefaultStream();
 440   } else {
 441     steady_state_time = 8 * number_of_streams;
 442     int bitrate_sum = 0;
 443     int kBitrateDenom = number_of_streams * (number_of_streams - 1);
 444     for (int i = 0; i < number_of_streams; i++) {
 445       // First stream gets half available bitrate, while the rest share the
 446       // remaining half i.e.: 1/2 = Sum[n/(N*(N-1))] for n=1..N-1 (rounded up)
 447       int bitrate = kStartBitrate / 2;
 448       if (i > 0) {
 449         bitrate = (kStartBitrate * i + kBitrateDenom / 2) / kBitrateDenom;
 450       }
 451       stream_generator_->AddStream(new testing::RtpStream(
 452           kFramerate,                     // Frames per second.
 453           bitrate,                        // Bitrate.
 454           kDefaultSsrc + i,               // SSRC.
 455           90000,                          // RTP frequency.
 456           0xFFFFF000 ^ (~0 << (32 - i)),  // Timestamp offset.
 457           0));                            // RTCP receive time.
 458       bitrate_sum += bitrate;
 459     }
 460     ASSERT_EQ(bitrate_sum, kStartBitrate);
 461   }
 462   if (wrap_time_stamp) {
 463     stream_generator_->set_rtp_timestamp_offset(kDefaultSsrc,
 464         std::numeric_limits<uint32_t>::max() - steady_state_time * 90000);
 465   }
 466
 467   // Run in steady state to make the estimator converge.
 468   stream_generator_->set_capacity_bps(kInitialCapacityBps);
 469   unsigned int bitrate_bps = SteadyStateRun(kDefaultSsrc,
 470                                             steady_state_time * kFramerate,
 471                                             kStartBitrate,
 472                                             kMinExpectedBitrate,
 473                                             kMaxExpectedBitrate,
 474                                             kInitialCapacityBps);
 475   EXPECT_NEAR(kInitialCapacityBps, bitrate_bps, 100000u);
 476   bitrate_observer_->Reset();
 477
 478   // Reduce the capacity and verify the decrease time.
 479   stream_generator_->set_capacity_bps(kReducedCapacityBps);
 480   int64_t overuse_start_time = clock_.TimeInMilliseconds();
 481   int64_t bitrate_drop_time = -1;
 482   for (int i = 0; i < 100 * number_of_streams; ++i) {
 483     GenerateAndProcessFrame(kDefaultSsrc, bitrate_bps);
 484     // Check for either increase or decrease.
 485     if (bitrate_observer_->updated()) {
 486       if (bitrate_drop_time == -1 &&
 487           bitrate_observer_->latest_bitrate() <= kReducedCapacityBps) {
 488         bitrate_drop_time = clock_.TimeInMilliseconds();
 489       }
 490       bitrate_bps = bitrate_observer_->latest_bitrate();
 491       bitrate_observer_->Reset();
 492     }
 493   }
 494
 495   EXPECT_EQ(expected_bitrate_drop_delta,
 496             bitrate_drop_time - overuse_start_time);
 497
 498   // Remove stream one by one.
 499   unsigned int latest_bps = 0;
 500   std::vector<unsigned int> ssrcs;
 501   for (int i = 0; i < number_of_streams; i++) {
 502     EXPECT_TRUE(bitrate_estimator_->LatestEstimate(&ssrcs, &latest_bps));
 503     EXPECT_EQ(number_of_streams - i, static_cast<int>(ssrcs.size()));
 504     EXPECT_EQ(bitrate_bps, latest_bps);
 505     for (int j = i; j < number_of_streams; j++) {
 506       EXPECT_EQ(kDefaultSsrc + j, ssrcs[j - i]);
 507     }
 508     bitrate_estimator_->RemoveStream(kDefaultSsrc + i);
 509   }
 510   EXPECT_TRUE(bitrate_estimator_->LatestEstimate(&ssrcs, &latest_bps));
 511   EXPECT_EQ(0u, ssrcs.size());
 512   EXPECT_EQ(0u, latest_bps);
 513 }
 514 }  // namespace webrtc