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
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
|
/*
* Copyright (c) 2019 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 "modules/video_coding/loss_notification_controller.h"
#include <stdint.h>
#include <cstddef>
#include "api/array_view.h"
#include "api/sequence_checker.h"
#include "modules/include/module_common_types.h"
#include "rtc_base/checks.h"
#include "rtc_base/logging.h"
#include "rtc_base/numerics/sequence_number_util.h"
namespace webrtc {
namespace {
// Keep a container's size no higher than `max_allowed_size`, by paring its size
// down to `target_size` whenever it has more than `max_allowed_size` elements.
template <typename Container>
void PareDown(Container* container,
size_t max_allowed_size,
size_t target_size) {
if (container->size() > max_allowed_size) {
const size_t entries_to_delete = container->size() - target_size;
auto erase_to = container->begin();
std::advance(erase_to, entries_to_delete);
container->erase(container->begin(), erase_to);
RTC_DCHECK_EQ(container->size(), target_size);
}
}
} // namespace
LossNotificationController::LossNotificationController(
KeyFrameRequestSender* key_frame_request_sender,
LossNotificationSender* loss_notification_sender)
: key_frame_request_sender_(key_frame_request_sender),
loss_notification_sender_(loss_notification_sender),
current_frame_potentially_decodable_(true) {
RTC_DCHECK(key_frame_request_sender_);
RTC_DCHECK(loss_notification_sender_);
}
LossNotificationController::~LossNotificationController() = default;
void LossNotificationController::OnReceivedPacket(
uint16_t rtp_seq_num,
const LossNotificationController::FrameDetails* frame) {
RTC_DCHECK_RUN_ON(&sequence_checker_);
// Ignore repeated or reordered packets.
// TODO(bugs.webrtc.org/10336): Handle packet reordering.
if (last_received_seq_num_ &&
!AheadOf(rtp_seq_num, *last_received_seq_num_)) {
return;
}
DiscardOldInformation(); // Prevent memory overconsumption.
const bool seq_num_gap =
last_received_seq_num_ &&
rtp_seq_num != static_cast<uint16_t>(*last_received_seq_num_ + 1u);
last_received_seq_num_ = rtp_seq_num;
// `frame` is not nullptr iff the packet is the first packet in the frame.
if (frame != nullptr) {
// Ignore repeated or reordered frames.
// TODO(bugs.webrtc.org/10336): Handle frame reordering.
if (last_received_frame_id_.has_value() &&
frame->frame_id <= last_received_frame_id_.value()) {
RTC_LOG(LS_WARNING) << "Repeated or reordered frame ID ("
<< frame->frame_id << ").";
return;
}
last_received_frame_id_ = frame->frame_id;
if (frame->is_keyframe) {
// Subsequent frames may not rely on frames before the key frame.
// Note that upon receiving a key frame, we do not issue a loss
// notification on RTP sequence number gap, unless that gap spanned
// the key frame itself. This is because any loss which occurred before
// the key frame is no longer relevant.
decodable_frame_ids_.clear();
current_frame_potentially_decodable_ = true;
} else {
const bool all_dependencies_decodable =
AllDependenciesDecodable(frame->frame_dependencies);
current_frame_potentially_decodable_ = all_dependencies_decodable;
if (seq_num_gap || !current_frame_potentially_decodable_) {
HandleLoss(rtp_seq_num, current_frame_potentially_decodable_);
}
}
} else if (seq_num_gap || !current_frame_potentially_decodable_) {
current_frame_potentially_decodable_ = false;
// We allow sending multiple loss notifications for a single frame
// even if only one of its packets is lost. We do this because the bigger
// the frame, the more likely it is to be non-discardable, and therefore
// the more robust we wish to be to loss of the feedback messages.
HandleLoss(rtp_seq_num, false);
}
}
void LossNotificationController::OnAssembledFrame(
uint16_t first_seq_num,
int64_t frame_id,
bool discardable,
ArrayView<const int64_t> frame_dependencies) {
RTC_DCHECK_RUN_ON(&sequence_checker_);
DiscardOldInformation(); // Prevent memory overconsumption.
if (discardable) {
return;
}
if (!AllDependenciesDecodable(frame_dependencies)) {
return;
}
last_decodable_non_discardable_.emplace(first_seq_num);
const auto it = decodable_frame_ids_.insert(frame_id);
RTC_DCHECK(it.second);
}
void LossNotificationController::DiscardOldInformation() {
constexpr size_t kExpectedKeyFrameIntervalFrames = 3000;
constexpr size_t kMaxSize = 2 * kExpectedKeyFrameIntervalFrames;
constexpr size_t kTargetSize = kExpectedKeyFrameIntervalFrames;
PareDown(&decodable_frame_ids_, kMaxSize, kTargetSize);
}
bool LossNotificationController::AllDependenciesDecodable(
ArrayView<const int64_t> frame_dependencies) const {
RTC_DCHECK_RUN_ON(&sequence_checker_);
// Due to packet reordering, frame buffering and asynchronous decoders, it is
// infeasible to make reliable conclusions on the decodability of a frame
// immediately when it arrives. We use the following assumptions:
// * Intra frames are decodable.
// * Inter frames are decodable if all of their references were decodable.
// One possibility that is ignored, is that the packet may be corrupt.
for (int64_t ref_frame_id : frame_dependencies) {
const auto ref_frame_it = decodable_frame_ids_.find(ref_frame_id);
if (ref_frame_it == decodable_frame_ids_.end()) {
// Reference frame not decodable.
return false;
}
}
return true;
}
void LossNotificationController::HandleLoss(uint16_t last_received_seq_num,
bool decodability_flag) {
RTC_DCHECK_RUN_ON(&sequence_checker_);
if (last_decodable_non_discardable_) {
RTC_DCHECK(AheadOf(last_received_seq_num,
last_decodable_non_discardable_->first_seq_num));
loss_notification_sender_->SendLossNotification(
last_decodable_non_discardable_->first_seq_num, last_received_seq_num,
decodability_flag, /*buffering_allowed=*/true);
} else {
key_frame_request_sender_->RequestKeyFrame();
}
}
} // namespace webrtc
|
