1 /*
2 * Copyright (c) 2017 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
11 #include "modules/congestion_controller/bitrate_estimator.h"
12
13 #include <cmath>
14
15 #include "modules/remote_bitrate_estimator/test/bwe_test_logging.h"
16 #include "modules/rtp_rtcp/include/rtp_rtcp_defines.h"
17
18 namespace webrtc {
19
20 namespace {
21 constexpr int kInitialRateWindowMs = 500;
22 constexpr int kRateWindowMs = 150;
23 } // namespace
24
BitrateEstimator()25 BitrateEstimator::BitrateEstimator()
26 : sum_(0),
27 current_win_ms_(0),
28 prev_time_ms_(-1),
29 bitrate_estimate_(-1.0f),
30 bitrate_estimate_var_(50.0f) {}
31
32 BitrateEstimator::~BitrateEstimator() = default;
33
Update(int64_t now_ms,int bytes)34 void BitrateEstimator::Update(int64_t now_ms, int bytes) {
35 int rate_window_ms = kRateWindowMs;
36 // We use a larger window at the beginning to get a more stable sample that
37 // we can use to initialize the estimate.
38 if (bitrate_estimate_ < 0.f)
39 rate_window_ms = kInitialRateWindowMs;
40 float bitrate_sample = UpdateWindow(now_ms, bytes, rate_window_ms);
41 if (bitrate_sample < 0.0f)
42 return;
43 if (bitrate_estimate_ < 0.0f) {
44 // This is the very first sample we get. Use it to initialize the estimate.
45 bitrate_estimate_ = bitrate_sample;
46 return;
47 }
48 // Define the sample uncertainty as a function of how far away it is from the
49 // current estimate.
50 float sample_uncertainty =
51 10.0f * std::abs(bitrate_estimate_ - bitrate_sample) / bitrate_estimate_;
52 float sample_var = sample_uncertainty * sample_uncertainty;
53 // Update a bayesian estimate of the rate, weighting it lower if the sample
54 // uncertainty is large.
55 // The bitrate estimate uncertainty is increased with each update to model
56 // that the bitrate changes over time.
57 float pred_bitrate_estimate_var = bitrate_estimate_var_ + 5.f;
58 bitrate_estimate_ = (sample_var * bitrate_estimate_ +
59 pred_bitrate_estimate_var * bitrate_sample) /
60 (sample_var + pred_bitrate_estimate_var);
61 bitrate_estimate_var_ = sample_var * pred_bitrate_estimate_var /
62 (sample_var + pred_bitrate_estimate_var);
63 BWE_TEST_LOGGING_PLOT(1, "acknowledged_bitrate", now_ms,
64 bitrate_estimate_ * 1000);
65 }
66
UpdateWindow(int64_t now_ms,int bytes,int rate_window_ms)67 float BitrateEstimator::UpdateWindow(int64_t now_ms,
68 int bytes,
69 int rate_window_ms) {
70 // Reset if time moves backwards.
71 if (now_ms < prev_time_ms_) {
72 prev_time_ms_ = -1;
73 sum_ = 0;
74 current_win_ms_ = 0;
75 }
76 if (prev_time_ms_ >= 0) {
77 current_win_ms_ += now_ms - prev_time_ms_;
78 // Reset if nothing has been received for more than a full window.
79 if (now_ms - prev_time_ms_ > rate_window_ms) {
80 sum_ = 0;
81 current_win_ms_ %= rate_window_ms;
82 }
83 }
84 prev_time_ms_ = now_ms;
85 float bitrate_sample = -1.0f;
86 if (current_win_ms_ >= rate_window_ms) {
87 bitrate_sample = 8.0f * sum_ / static_cast<float>(rate_window_ms);
88 current_win_ms_ -= rate_window_ms;
89 sum_ = 0;
90 }
91 sum_ += bytes;
92 return bitrate_sample;
93 }
94
bitrate_bps() const95 rtc::Optional<uint32_t> BitrateEstimator::bitrate_bps() const {
96 if (bitrate_estimate_ < 0.f)
97 return rtc::nullopt;
98 return bitrate_estimate_ * 1000;
99 }
100
ExpectFastRateChange()101 void BitrateEstimator::ExpectFastRateChange() {
102 // By setting the bitrate-estimate variance to a higher value we allow the
103 // bitrate to change fast for the next few samples.
104 bitrate_estimate_var_ += 200;
105 }
106
107 } // namespace webrtc
108