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/*
* Copyright (c) 2012 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 <vector>
#include "testing/gtest/include/gtest/gtest.h"
#include "webrtc/call/mock/mock_rtc_event_log.h"
#include "webrtc/modules/bitrate_controller/include/bitrate_controller.h"
#include "webrtc/modules/pacing/mock/mock_paced_sender.h"
#include "webrtc/modules/rtp_rtcp/include/rtp_rtcp_defines.h"
#include "webrtc/test/field_trial.h"
using ::testing::Exactly;
using ::testing::Return;
using webrtc::BitrateController;
using webrtc::BitrateObserver;
using webrtc::PacedSender;
using webrtc::RtcpBandwidthObserver;
uint8_t WeightedLoss(int num_packets1, uint8_t fraction_loss1,
int num_packets2, uint8_t fraction_loss2) {
int weighted_sum = num_packets1 * fraction_loss1 +
num_packets2 * fraction_loss2;
int total_num_packets = num_packets1 + num_packets2;
return (weighted_sum + total_num_packets / 2) / total_num_packets;
}
webrtc::RTCPReportBlock CreateReportBlock(
uint32_t remote_ssrc, uint32_t source_ssrc,
uint8_t fraction_lost, uint32_t extended_high_sequence_number) {
return webrtc::RTCPReportBlock(remote_ssrc, source_ssrc, fraction_lost, 0,
extended_high_sequence_number, 0, 0, 0);
}
class TestBitrateObserver: public BitrateObserver {
public:
TestBitrateObserver()
: last_bitrate_(0),
last_fraction_loss_(0),
last_rtt_(0) {
}
virtual void OnNetworkChanged(uint32_t bitrate,
uint8_t fraction_loss,
int64_t rtt) {
last_bitrate_ = static_cast<int>(bitrate);
last_fraction_loss_ = fraction_loss;
last_rtt_ = rtt;
}
int last_bitrate_;
uint8_t last_fraction_loss_;
int64_t last_rtt_;
};
class BitrateControllerTest : public ::testing::Test {
protected:
BitrateControllerTest() : clock_(0) {}
~BitrateControllerTest() {}
virtual void SetUp() {
controller_.reset(BitrateController::CreateBitrateController(
&clock_, &bitrate_observer_, &event_log_));
controller_->SetStartBitrate(kStartBitrateBps);
EXPECT_EQ(kStartBitrateBps, bitrate_observer_.last_bitrate_);
controller_->SetMinMaxBitrate(kMinBitrateBps, kMaxBitrateBps);
EXPECT_EQ(kStartBitrateBps, bitrate_observer_.last_bitrate_);
bandwidth_observer_.reset(controller_->CreateRtcpBandwidthObserver());
}
virtual void TearDown() {
}
const int kMinBitrateBps = 100000;
const int kStartBitrateBps = 200000;
const int kMaxBitrateBps = 300000;
const int kDefaultMinBitrateBps = 10000;
const int kDefaultMaxBitrateBps = 1000000000;
webrtc::SimulatedClock clock_;
TestBitrateObserver bitrate_observer_;
std::unique_ptr<BitrateController> controller_;
std::unique_ptr<RtcpBandwidthObserver> bandwidth_observer_;
testing::NiceMock<webrtc::MockRtcEventLog> event_log_;
};
TEST_F(BitrateControllerTest, DefaultMinMaxBitrate) {
// Receive successively lower REMBs, verify the reserved bitrate is deducted.
controller_->SetMinMaxBitrate(0, 0);
EXPECT_EQ(kStartBitrateBps, bitrate_observer_.last_bitrate_);
bandwidth_observer_->OnReceivedEstimatedBitrate(kDefaultMinBitrateBps / 2);
EXPECT_EQ(kDefaultMinBitrateBps, bitrate_observer_.last_bitrate_);
bandwidth_observer_->OnReceivedEstimatedBitrate(2 * kDefaultMaxBitrateBps);
clock_.AdvanceTimeMilliseconds(1000);
controller_->Process();
EXPECT_EQ(kDefaultMaxBitrateBps, bitrate_observer_.last_bitrate_);
}
TEST_F(BitrateControllerTest, OneBitrateObserverOneRtcpObserver) {
// First REMB applies immediately.
int64_t time_ms = 1001;
webrtc::ReportBlockList report_blocks;
report_blocks.push_back(CreateReportBlock(1, 2, 0, 1));
bandwidth_observer_->OnReceivedEstimatedBitrate(200000);
EXPECT_EQ(200000, bitrate_observer_.last_bitrate_);
EXPECT_EQ(0, bitrate_observer_.last_fraction_loss_);
EXPECT_EQ(0, bitrate_observer_.last_rtt_);
bandwidth_observer_->OnReceivedRtcpReceiverReport(report_blocks, 50, time_ms);
report_blocks.clear();
time_ms += 2000;
// Receive a high remb, test bitrate inc.
bandwidth_observer_->OnReceivedEstimatedBitrate(400000);
// Test bitrate increase 8% per second.
report_blocks.push_back(CreateReportBlock(1, 2, 0, 21));
bandwidth_observer_->OnReceivedRtcpReceiverReport(report_blocks, 50, time_ms);
EXPECT_EQ(217000, bitrate_observer_.last_bitrate_);
EXPECT_EQ(0, bitrate_observer_.last_fraction_loss_);
EXPECT_EQ(50, bitrate_observer_.last_rtt_);
time_ms += 1000;
report_blocks.clear();
report_blocks.push_back(CreateReportBlock(1, 2, 0, 41));
bandwidth_observer_->OnReceivedRtcpReceiverReport(report_blocks, 50, time_ms);
EXPECT_EQ(235360, bitrate_observer_.last_bitrate_);
EXPECT_EQ(0, bitrate_observer_.last_fraction_loss_);
EXPECT_EQ(50, bitrate_observer_.last_rtt_);
time_ms += 1000;
report_blocks.clear();
report_blocks.push_back(CreateReportBlock(1, 2, 0, 61));
bandwidth_observer_->OnReceivedRtcpReceiverReport(report_blocks, 50, time_ms);
EXPECT_EQ(255189, bitrate_observer_.last_bitrate_);
time_ms += 1000;
report_blocks.clear();
report_blocks.push_back(CreateReportBlock(1, 2, 0, 81));
bandwidth_observer_->OnReceivedRtcpReceiverReport(report_blocks, 50, time_ms);
EXPECT_EQ(276604, bitrate_observer_.last_bitrate_);
time_ms += 1000;
report_blocks.clear();
report_blocks.push_back(CreateReportBlock(1, 2, 0, 101));
bandwidth_observer_->OnReceivedRtcpReceiverReport(report_blocks, 50, time_ms);
EXPECT_EQ(299732, bitrate_observer_.last_bitrate_);
time_ms += 1000;
// Reach max cap.
report_blocks.clear();
report_blocks.push_back(CreateReportBlock(1, 2, 0, 121));
bandwidth_observer_->OnReceivedRtcpReceiverReport(report_blocks, 50, time_ms);
EXPECT_EQ(300000, bitrate_observer_.last_bitrate_);
time_ms += 1000;
report_blocks.clear();
report_blocks.push_back(CreateReportBlock(1, 2, 0, 141));
bandwidth_observer_->OnReceivedRtcpReceiverReport(report_blocks, 50, time_ms);
EXPECT_EQ(300000, bitrate_observer_.last_bitrate_);
// Test that a low delay-based estimate limits the combined estimate.
controller_->OnReceiveBitrateChanged({0}, 280000);
EXPECT_EQ(280000, bitrate_observer_.last_bitrate_);
// Test that a low REMB limits the combined estimate.
bandwidth_observer_->OnReceivedEstimatedBitrate(250000);
EXPECT_EQ(250000, bitrate_observer_.last_bitrate_);
EXPECT_EQ(0, bitrate_observer_.last_fraction_loss_);
EXPECT_EQ(50, bitrate_observer_.last_rtt_);
bandwidth_observer_->OnReceivedEstimatedBitrate(1000);
EXPECT_EQ(100000, bitrate_observer_.last_bitrate_);
}
TEST_F(BitrateControllerTest, OneBitrateObserverTwoRtcpObservers) {
const uint32_t kSsrc1 = 1;
const uint32_t kSsrc2 = 2;
// REMBs during the first 2 seconds apply immediately.
int64_t time_ms = 1;
webrtc::ReportBlockList report_blocks;
report_blocks.push_back(CreateReportBlock(kSsrc1, 2, 0, 1));
bandwidth_observer_->OnReceivedRtcpReceiverReport(report_blocks, 50, time_ms);
report_blocks.clear();
time_ms += 500;
RtcpBandwidthObserver* second_bandwidth_observer =
controller_->CreateRtcpBandwidthObserver();
// Test start bitrate.
report_blocks.push_back(CreateReportBlock(2, 2, 0, 21));
second_bandwidth_observer->OnReceivedRtcpReceiverReport(
report_blocks, 100, 1);
EXPECT_EQ(200000, bitrate_observer_.last_bitrate_);
EXPECT_EQ(0, bitrate_observer_.last_fraction_loss_);
EXPECT_EQ(100, bitrate_observer_.last_rtt_);
time_ms += 500;
// Test bitrate increase 8% per second.
report_blocks.clear();
report_blocks.push_back(CreateReportBlock(kSsrc1, 2, 0, 21));
bandwidth_observer_->OnReceivedRtcpReceiverReport(report_blocks, 50, time_ms);
time_ms += 500;
report_blocks.front().remoteSSRC = kSsrc2;
second_bandwidth_observer->OnReceivedRtcpReceiverReport(
report_blocks, 100, time_ms);
EXPECT_EQ(217000, bitrate_observer_.last_bitrate_);
EXPECT_EQ(0, bitrate_observer_.last_fraction_loss_);
EXPECT_EQ(100, bitrate_observer_.last_rtt_);
time_ms += 500;
// Extra report should not change estimate.
report_blocks.clear();
report_blocks.push_back(CreateReportBlock(kSsrc2, 2, 0, 31));
second_bandwidth_observer->OnReceivedRtcpReceiverReport(
report_blocks, 100, time_ms);
EXPECT_EQ(217000, bitrate_observer_.last_bitrate_);
time_ms += 500;
report_blocks.clear();
report_blocks.push_back(CreateReportBlock(kSsrc1, 2, 0, 41));
bandwidth_observer_->OnReceivedRtcpReceiverReport(report_blocks, 50, time_ms);
EXPECT_EQ(235360, bitrate_observer_.last_bitrate_);
// Second report should not change estimate.
report_blocks.clear();
report_blocks.push_back(CreateReportBlock(kSsrc2, 2, 0, 41));
second_bandwidth_observer->OnReceivedRtcpReceiverReport(
report_blocks, 100, time_ms);
EXPECT_EQ(235360, bitrate_observer_.last_bitrate_);
time_ms += 1000;
// Reports from only one bandwidth observer is ok.
report_blocks.clear();
report_blocks.push_back(CreateReportBlock(kSsrc2, 2, 0, 61));
second_bandwidth_observer->OnReceivedRtcpReceiverReport(
report_blocks, 50, time_ms);
EXPECT_EQ(255189, bitrate_observer_.last_bitrate_);
time_ms += 1000;
report_blocks.clear();
report_blocks.push_back(CreateReportBlock(kSsrc2, 2, 0, 81));
second_bandwidth_observer->OnReceivedRtcpReceiverReport(
report_blocks, 50, time_ms);
EXPECT_EQ(276604, bitrate_observer_.last_bitrate_);
time_ms += 1000;
report_blocks.clear();
report_blocks.push_back(CreateReportBlock(kSsrc2, 2, 0, 121));
second_bandwidth_observer->OnReceivedRtcpReceiverReport(
report_blocks, 50, time_ms);
EXPECT_EQ(299732, bitrate_observer_.last_bitrate_);
time_ms += 1000;
// Reach max cap.
report_blocks.clear();
report_blocks.push_back(CreateReportBlock(kSsrc2, 2, 0, 141));
second_bandwidth_observer->OnReceivedRtcpReceiverReport(
report_blocks, 50, time_ms);
EXPECT_EQ(300000, bitrate_observer_.last_bitrate_);
// Test that a low REMB trigger immediately.
// We don't care which bandwidth observer that delivers the REMB.
second_bandwidth_observer->OnReceivedEstimatedBitrate(250000);
EXPECT_EQ(250000, bitrate_observer_.last_bitrate_);
EXPECT_EQ(0, bitrate_observer_.last_fraction_loss_);
EXPECT_EQ(50, bitrate_observer_.last_rtt_);
// Min cap.
bandwidth_observer_->OnReceivedEstimatedBitrate(1000);
EXPECT_EQ(100000, bitrate_observer_.last_bitrate_);
delete second_bandwidth_observer;
}
TEST_F(BitrateControllerTest, OneBitrateObserverMultipleReportBlocks) {
uint32_t sequence_number[2] = {0, 0xFF00};
const int kStartBitrate = 200000;
const int kMinBitrate = 100000;
const int kMaxBitrate = 300000;
controller_->SetStartBitrate(kStartBitrate);
controller_->SetMinMaxBitrate(kMinBitrate, kMaxBitrate);
// REMBs during the first 2 seconds apply immediately.
int64_t time_ms = 1001;
webrtc::ReportBlockList report_blocks;
report_blocks.push_back(CreateReportBlock(1, 2, 0, sequence_number[0]));
bandwidth_observer_->OnReceivedEstimatedBitrate(kStartBitrate);
bandwidth_observer_->OnReceivedRtcpReceiverReport(report_blocks, 50, time_ms);
report_blocks.clear();
time_ms += 2000;
// Receive a high REMB, test bitrate increase.
bandwidth_observer_->OnReceivedEstimatedBitrate(400000);
int last_bitrate = 0;
// Ramp up to max bitrate.
for (int i = 0; i < 7; ++i) {
report_blocks.push_back(CreateReportBlock(1, 2, 0, sequence_number[0]));
report_blocks.push_back(CreateReportBlock(1, 3, 0, sequence_number[1]));
bandwidth_observer_->OnReceivedRtcpReceiverReport(report_blocks, 50,
time_ms);
EXPECT_GT(bitrate_observer_.last_bitrate_, last_bitrate);
EXPECT_EQ(0, bitrate_observer_.last_fraction_loss_);
EXPECT_EQ(50, bitrate_observer_.last_rtt_);
last_bitrate = bitrate_observer_.last_bitrate_;
time_ms += 1000;
sequence_number[0] += 20;
sequence_number[1] += 1;
report_blocks.clear();
}
EXPECT_EQ(kMaxBitrate, bitrate_observer_.last_bitrate_);
// Packet loss on the first stream. Verify that bitrate decreases.
report_blocks.push_back(CreateReportBlock(1, 2, 50, sequence_number[0]));
report_blocks.push_back(CreateReportBlock(1, 3, 0, sequence_number[1]));
bandwidth_observer_->OnReceivedRtcpReceiverReport(report_blocks, 50, time_ms);
EXPECT_LT(bitrate_observer_.last_bitrate_, last_bitrate);
EXPECT_EQ(WeightedLoss(20, 50, 1, 0), bitrate_observer_.last_fraction_loss_);
EXPECT_EQ(50, bitrate_observer_.last_rtt_);
last_bitrate = bitrate_observer_.last_bitrate_;
sequence_number[0] += 20;
sequence_number[1] += 20;
time_ms += 1000;
report_blocks.clear();
// Packet loss on the second stream. Verify that bitrate decreases.
report_blocks.push_back(CreateReportBlock(1, 2, 0, sequence_number[0]));
report_blocks.push_back(CreateReportBlock(1, 3, 75, sequence_number[1]));
bandwidth_observer_->OnReceivedRtcpReceiverReport(report_blocks, 50, time_ms);
EXPECT_LT(bitrate_observer_.last_bitrate_, last_bitrate);
EXPECT_EQ(WeightedLoss(20, 0, 20, 75), bitrate_observer_.last_fraction_loss_);
EXPECT_EQ(50, bitrate_observer_.last_rtt_);
last_bitrate = bitrate_observer_.last_bitrate_;
sequence_number[0] += 20;
sequence_number[1] += 1;
time_ms += 1000;
report_blocks.clear();
// All packets lost on stream with few packets, no back-off.
report_blocks.push_back(CreateReportBlock(1, 2, 1, sequence_number[0]));
report_blocks.push_back(CreateReportBlock(1, 3, 255, sequence_number[1]));
bandwidth_observer_->OnReceivedRtcpReceiverReport(report_blocks, 50, time_ms);
EXPECT_EQ(bitrate_observer_.last_bitrate_, last_bitrate);
EXPECT_EQ(WeightedLoss(20, 1, 1, 255), bitrate_observer_.last_fraction_loss_);
EXPECT_EQ(50, bitrate_observer_.last_rtt_);
last_bitrate = bitrate_observer_.last_bitrate_;
sequence_number[0] += 20;
sequence_number[1] += 1;
report_blocks.clear();
}
TEST_F(BitrateControllerTest, SetReservedBitrate) {
// Receive successively lower REMBs, verify the reserved bitrate is deducted.
controller_->SetReservedBitrate(0);
bandwidth_observer_->OnReceivedEstimatedBitrate(400000);
EXPECT_EQ(200000, bitrate_observer_.last_bitrate_);
controller_->SetReservedBitrate(50000);
bandwidth_observer_->OnReceivedEstimatedBitrate(400000);
EXPECT_EQ(150000, bitrate_observer_.last_bitrate_);
controller_->SetReservedBitrate(0);
bandwidth_observer_->OnReceivedEstimatedBitrate(250000);
EXPECT_EQ(200000, bitrate_observer_.last_bitrate_);
controller_->SetReservedBitrate(50000);
bandwidth_observer_->OnReceivedEstimatedBitrate(250000);
EXPECT_EQ(150000, bitrate_observer_.last_bitrate_);
controller_->SetReservedBitrate(0);
bandwidth_observer_->OnReceivedEstimatedBitrate(200000);
EXPECT_EQ(200000, bitrate_observer_.last_bitrate_);
controller_->SetReservedBitrate(30000);
bandwidth_observer_->OnReceivedEstimatedBitrate(200000);
EXPECT_EQ(170000, bitrate_observer_.last_bitrate_);
controller_->SetReservedBitrate(0);
bandwidth_observer_->OnReceivedEstimatedBitrate(160000);
EXPECT_EQ(160000, bitrate_observer_.last_bitrate_);
controller_->SetReservedBitrate(30000);
bandwidth_observer_->OnReceivedEstimatedBitrate(160000);
EXPECT_EQ(130000, bitrate_observer_.last_bitrate_);
controller_->SetReservedBitrate(0);
bandwidth_observer_->OnReceivedEstimatedBitrate(120000);
EXPECT_EQ(120000, bitrate_observer_.last_bitrate_);
controller_->SetReservedBitrate(10000);
bandwidth_observer_->OnReceivedEstimatedBitrate(120000);
EXPECT_EQ(110000, bitrate_observer_.last_bitrate_);
controller_->SetReservedBitrate(0);
bandwidth_observer_->OnReceivedEstimatedBitrate(120000);
EXPECT_EQ(120000, bitrate_observer_.last_bitrate_);
controller_->SetReservedBitrate(50000);
bandwidth_observer_->OnReceivedEstimatedBitrate(120000);
// Limited by min bitrate.
EXPECT_EQ(100000, bitrate_observer_.last_bitrate_);
controller_->SetReservedBitrate(10000);
bandwidth_observer_->OnReceivedEstimatedBitrate(1);
EXPECT_EQ(100000, bitrate_observer_.last_bitrate_);
}
TEST_F(BitrateControllerTest, TimeoutsWithoutFeedback) {
{
webrtc::test::ScopedFieldTrials override_field_trials(
"WebRTC-SendSideBwe/Enabled/");
SetUp();
int expected_bitrate_bps = 300000;
controller_->SetBitrates(300000, kDefaultMinBitrateBps,
kDefaultMaxBitrateBps);
webrtc::ReportBlockList report_blocks;
report_blocks.push_back(CreateReportBlock(1, 2, 0, 1));
bandwidth_observer_->OnReceivedRtcpReceiverReport(
report_blocks, 50, clock_.TimeInMilliseconds());
EXPECT_EQ(expected_bitrate_bps, bitrate_observer_.last_bitrate_);
clock_.AdvanceTimeMilliseconds(500);
report_blocks.push_back(CreateReportBlock(1, 2, 0, 21));
bandwidth_observer_->OnReceivedRtcpReceiverReport(
report_blocks, 50, clock_.TimeInMilliseconds());
report_blocks.clear();
expected_bitrate_bps = expected_bitrate_bps * 1.08 + 1000;
EXPECT_EQ(expected_bitrate_bps, bitrate_observer_.last_bitrate_);
clock_.AdvanceTimeMilliseconds(1500);
report_blocks.push_back(CreateReportBlock(1, 2, 0, 41));
bandwidth_observer_->OnReceivedRtcpReceiverReport(
report_blocks, 50, clock_.TimeInMilliseconds());
expected_bitrate_bps = expected_bitrate_bps * 1.08 + 1000;
EXPECT_EQ(expected_bitrate_bps, bitrate_observer_.last_bitrate_);
clock_.AdvanceTimeMilliseconds(1000);
// 1 seconds since feedback, expect increase.
controller_->Process();
expected_bitrate_bps = expected_bitrate_bps * 1.08 + 1000;
EXPECT_EQ(expected_bitrate_bps, bitrate_observer_.last_bitrate_);
clock_.AdvanceTimeMilliseconds(800);
// 1.8 seconds since feedback, expect no increase.
controller_->Process();
EXPECT_EQ(expected_bitrate_bps, bitrate_observer_.last_bitrate_);
clock_.AdvanceTimeMilliseconds(3701);
// More than 4.5 seconds since feedback, expect decrease.
controller_->Process();
expected_bitrate_bps *= 0.8;
EXPECT_EQ(expected_bitrate_bps, bitrate_observer_.last_bitrate_);
clock_.AdvanceTimeMilliseconds(500);
// Only one timeout every second.
controller_->Process();
EXPECT_EQ(expected_bitrate_bps, bitrate_observer_.last_bitrate_);
clock_.AdvanceTimeMilliseconds(501);
// New timeout allowed.
controller_->Process();
expected_bitrate_bps *= 0.8;
EXPECT_EQ(expected_bitrate_bps, bitrate_observer_.last_bitrate_);
}
}
TEST_F(BitrateControllerTest, StopIncreaseWithoutPacketReports) {
int expected_bitrate_bps = 300000;
controller_->SetBitrates(300000, kDefaultMinBitrateBps,
kDefaultMaxBitrateBps);
webrtc::ReportBlockList report_blocks;
report_blocks.push_back(CreateReportBlock(1, 2, 0, 1));
bandwidth_observer_->OnReceivedRtcpReceiverReport(
report_blocks, 50, clock_.TimeInMilliseconds());
EXPECT_EQ(expected_bitrate_bps, bitrate_observer_.last_bitrate_);
clock_.AdvanceTimeMilliseconds(500);
report_blocks.push_back(CreateReportBlock(1, 2, 0, 21));
bandwidth_observer_->OnReceivedRtcpReceiverReport(
report_blocks, 50, clock_.TimeInMilliseconds());
report_blocks.clear();
expected_bitrate_bps = expected_bitrate_bps * 1.08 + 1000;
EXPECT_EQ(expected_bitrate_bps, bitrate_observer_.last_bitrate_);
clock_.AdvanceTimeMilliseconds(1500);
// 1.2 seconds without packets reported as received, no increase.
report_blocks.push_back(CreateReportBlock(1, 2, 0, 21));
bandwidth_observer_->OnReceivedRtcpReceiverReport(
report_blocks, 50, clock_.TimeInMilliseconds());
EXPECT_EQ(expected_bitrate_bps, bitrate_observer_.last_bitrate_);
clock_.AdvanceTimeMilliseconds(1000);
// 5 packets reported as received since last, too few, no increase.
report_blocks.push_back(CreateReportBlock(1, 2, 0, 26));
bandwidth_observer_->OnReceivedRtcpReceiverReport(
report_blocks, 50, clock_.TimeInMilliseconds());
report_blocks.clear();
EXPECT_EQ(expected_bitrate_bps, bitrate_observer_.last_bitrate_);
clock_.AdvanceTimeMilliseconds(100);
// 15 packets reported as received since last, enough to increase.
report_blocks.push_back(CreateReportBlock(1, 2, 0, 41));
bandwidth_observer_->OnReceivedRtcpReceiverReport(
report_blocks, 50, clock_.TimeInMilliseconds());
expected_bitrate_bps = expected_bitrate_bps * 1.08 + 1000;
EXPECT_EQ(expected_bitrate_bps, bitrate_observer_.last_bitrate_);
clock_.AdvanceTimeMilliseconds(1000);
}