1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
|
// Copyright 2017 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "remoting/codec/encoder_bitrate_filter.h"
#include <algorithm>
#include <cstdlib>
namespace remoting {
namespace {
// Only update encoder bitrate when bandwidth changes by more than 33%. This
// value is chosen such that the codec is notified about significant changes in
// bandwidth, while ignoring bandwidth estimate noise. This is necessary because
// the encoder drops quality every time it's being reconfigured. When using VP8
// encoder in realtime mode, the encoded frame size correlates very poorly with
// the target bitrate, so it's not necessary to set target bitrate to match
// bandwidth exactly. Send bitrate is controlled more precisely by adjusting
// time intervals between frames (i.e. FPS).
constexpr int kEncoderBitrateChangePercentage = 33;
// We use a WeightedSamples to analyze the bandwidth to avoid a sharp change to
// significantly impact the image quality. By using the weight factor as 0.95,
// the weight of a bandwidth estimate one second ago (30 frames before) drops to
// ~21.5%.
constexpr double kBandwidthWeightFactor = 0.95;
} // namespace
EncoderBitrateFilter::EncoderBitrateFilter(
int minimum_bitrate_kbps_per_megapixel)
: minimum_bitrate_kbps_per_megapixel_(minimum_bitrate_kbps_per_megapixel),
bandwidth_kbps_(kBandwidthWeightFactor) {}
EncoderBitrateFilter::~EncoderBitrateFilter() = default;
void EncoderBitrateFilter::SetBandwidthEstimateKbps(int bandwidth_kbps) {
bandwidth_kbps_.Record(bandwidth_kbps);
int current_kbps = bandwidth_kbps_.WeightedAverage();
if (std::abs(current_kbps - bitrate_kbps_) >
bitrate_kbps_ * kEncoderBitrateChangePercentage / 100) {
bitrate_kbps_ = current_kbps;
}
}
void EncoderBitrateFilter::SetFrameSize(int width, int height) {
minimum_bitrate_kbps_ =
std::max(static_cast<int64_t>(minimum_bitrate_kbps_per_megapixel_) *
width * height / 1000000,
static_cast<int64_t>(minimum_bitrate_kbps_));
}
int EncoderBitrateFilter::GetTargetBitrateKbps() const {
return bitrate_kbps_;
}
} // namespace remoting
|
