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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 "modules/rtp_rtcp/source/ulpfec_generator.h"
#include <string.h>
#include <cstdint>
#include <memory>
#include <utility>
#include "modules/rtp_rtcp/include/rtp_rtcp_defines.h"
#include "modules/rtp_rtcp/source/byte_io.h"
#include "modules/rtp_rtcp/source/forward_error_correction.h"
#include "modules/rtp_rtcp/source/forward_error_correction_internal.h"
#include "modules/rtp_rtcp/source/rtp_utility.h"
#include "rtc_base/checks.h"
#include "rtc_base/critical_section.h"
namespace webrtc {
namespace {
constexpr size_t kRedForFecHeaderLength = 1;
// This controls the maximum amount of excess overhead (actual - target)
// allowed in order to trigger EncodeFec(), before |params_.max_fec_frames|
// is reached. Overhead here is defined as relative to number of media packets.
constexpr int kMaxExcessOverhead = 50; // Q8.
// This is the minimum number of media packets required (above some protection
// level) in order to trigger EncodeFec(), before |params_.max_fec_frames| is
// reached.
constexpr size_t kMinMediaPackets = 4;
// Threshold on the received FEC protection level, above which we enforce at
// least |kMinMediaPackets| packets for the FEC code. Below this
// threshold |kMinMediaPackets| is set to default value of 1.
//
// The range is between 0 and 255, where 255 corresponds to 100% overhead
// (relative to the number of protected media packets).
constexpr uint8_t kHighProtectionThreshold = 80;
// This threshold is used to adapt the |kMinMediaPackets| threshold, based
// on the average number of packets per frame seen so far. When there are few
// packets per frame (as given by this threshold), at least
// |kMinMediaPackets| + 1 packets are sent to the FEC code.
constexpr float kMinMediaPacketsAdaptationThreshold = 2.0f;
// At construction time, we don't know the SSRC that is used for the generated
// FEC packets, but we still need to give it to the ForwardErrorCorrection ctor
// to be used in the decoding.
// TODO(brandtr): Get rid of this awkwardness by splitting
// ForwardErrorCorrection in two objects -- one encoder and one decoder.
constexpr uint32_t kUnknownSsrc = 0;
} // namespace
UlpfecGenerator::Params::Params() = default;
UlpfecGenerator::Params::Params(FecProtectionParams delta_params,
FecProtectionParams keyframe_params)
: delta_params(delta_params), keyframe_params(keyframe_params) {}
UlpfecGenerator::UlpfecGenerator(int red_payload_type,
int ulpfec_payload_type,
Clock* clock)
: red_payload_type_(red_payload_type),
ulpfec_payload_type_(ulpfec_payload_type),
clock_(clock),
fec_(ForwardErrorCorrection::CreateUlpfec(kUnknownSsrc)),
num_protected_frames_(0),
min_num_media_packets_(1),
keyframe_in_process_(false),
fec_bitrate_(/*max_window_size_ms=*/1000, RateStatistics::kBpsScale) {}
// Used by FlexFecSender, payload types are unused.
UlpfecGenerator::UlpfecGenerator(std::unique_ptr<ForwardErrorCorrection> fec,
Clock* clock)
: red_payload_type_(0),
ulpfec_payload_type_(0),
clock_(clock),
fec_(std::move(fec)),
num_protected_frames_(0),
min_num_media_packets_(1),
keyframe_in_process_(false),
fec_bitrate_(/*max_window_size_ms=*/1000, RateStatistics::kBpsScale) {}
UlpfecGenerator::~UlpfecGenerator() = default;
void UlpfecGenerator::SetProtectionParameters(
const FecProtectionParams& delta_params,
const FecProtectionParams& key_params) {
RTC_DCHECK_GE(delta_params.fec_rate, 0);
RTC_DCHECK_LE(delta_params.fec_rate, 255);
RTC_DCHECK_GE(key_params.fec_rate, 0);
RTC_DCHECK_LE(key_params.fec_rate, 255);
// Store the new params and apply them for the next set of FEC packets being
// produced.
rtc::CritScope cs(&crit_);
pending_params_.emplace(delta_params, key_params);
}
void UlpfecGenerator::AddPacketAndGenerateFec(const RtpPacketToSend& packet) {
RTC_DCHECK_RUNS_SERIALIZED(&race_checker_);
RTC_DCHECK(generated_fec_packets_.empty());
if (media_packets_.empty()) {
rtc::CritScope cs(&crit_);
if (pending_params_) {
current_params_ = *pending_params_;
pending_params_.reset();
if (CurrentParams().fec_rate > kHighProtectionThreshold) {
min_num_media_packets_ = kMinMediaPackets;
} else {
min_num_media_packets_ = 1;
}
}
keyframe_in_process_ = packet.is_key_frame();
}
RTC_DCHECK_EQ(packet.is_key_frame(), keyframe_in_process_);
bool complete_frame = false;
const bool marker_bit = packet.Marker();
if (media_packets_.size() < kUlpfecMaxMediaPackets) {
// Our packet masks can only protect up to |kUlpfecMaxMediaPackets| packets.
auto fec_packet = std::make_unique<ForwardErrorCorrection::Packet>();
fec_packet->data = packet.Buffer();
media_packets_.push_back(std::move(fec_packet));
// Keep a copy of the last RTP packet, so we can copy the RTP header
// from it when creating newly generated ULPFEC+RED packets.
RTC_DCHECK_GE(packet.headers_size(), kRtpHeaderSize);
last_media_packet_ = packet;
}
if (marker_bit) {
++num_protected_frames_;
complete_frame = true;
}
auto params = CurrentParams();
// Produce FEC over at most |params_.max_fec_frames| frames, or as soon as:
// (1) the excess overhead (actual overhead - requested/target overhead) is
// less than |kMaxExcessOverhead|, and
// (2) at least |min_num_media_packets_| media packets is reached.
if (complete_frame &&
(num_protected_frames_ == params.max_fec_frames ||
(ExcessOverheadBelowMax() && MinimumMediaPacketsReached()))) {
// We are not using Unequal Protection feature of the parity erasure code.
constexpr int kNumImportantPackets = 0;
constexpr bool kUseUnequalProtection = false;
fec_->EncodeFec(media_packets_, params.fec_rate, kNumImportantPackets,
kUseUnequalProtection, params.fec_mask_type,
&generated_fec_packets_);
if (generated_fec_packets_.empty()) {
ResetState();
}
}
}
bool UlpfecGenerator::ExcessOverheadBelowMax() const {
RTC_DCHECK_RUNS_SERIALIZED(&race_checker_);
return ((Overhead() - CurrentParams().fec_rate) < kMaxExcessOverhead);
}
bool UlpfecGenerator::MinimumMediaPacketsReached() const {
RTC_DCHECK_RUNS_SERIALIZED(&race_checker_);
float average_num_packets_per_frame =
static_cast<float>(media_packets_.size()) / num_protected_frames_;
int num_media_packets = static_cast<int>(media_packets_.size());
if (average_num_packets_per_frame < kMinMediaPacketsAdaptationThreshold) {
return num_media_packets >= min_num_media_packets_;
} else {
// For larger rates (more packets/frame), increase the threshold.
// TODO(brandtr): Investigate what impact this adaptation has.
return num_media_packets >= min_num_media_packets_ + 1;
}
}
const FecProtectionParams& UlpfecGenerator::CurrentParams() const {
RTC_DCHECK_RUNS_SERIALIZED(&race_checker_);
return keyframe_in_process_ ? current_params_.keyframe_params
: current_params_.delta_params;
}
size_t UlpfecGenerator::MaxPacketOverhead() const {
RTC_DCHECK_RUNS_SERIALIZED(&race_checker_);
return fec_->MaxPacketOverhead();
}
std::vector<std::unique_ptr<RtpPacketToSend>> UlpfecGenerator::GetFecPackets() {
RTC_DCHECK_RUNS_SERIALIZED(&race_checker_);
if (generated_fec_packets_.empty()) {
return std::vector<std::unique_ptr<RtpPacketToSend>>();
}
// Wrap FEC packet (including FEC headers) in a RED packet. Since the
// FEC packets in |generated_fec_packets_| don't have RTP headers, we
// reuse the header from the last media packet.
RTC_CHECK(last_media_packet_.has_value());
last_media_packet_->SetPayloadSize(0);
std::vector<std::unique_ptr<RtpPacketToSend>> fec_packets;
fec_packets.reserve(generated_fec_packets_.size());
size_t total_fec_size_bytes = 0;
for (const auto* fec_packet : generated_fec_packets_) {
std::unique_ptr<RtpPacketToSend> red_packet =
std::make_unique<RtpPacketToSend>(*last_media_packet_);
red_packet->SetPayloadType(red_payload_type_);
red_packet->SetMarker(false);
uint8_t* payload_buffer = red_packet->SetPayloadSize(
kRedForFecHeaderLength + fec_packet->data.size());
// Primary RED header with F bit unset.
// See https://tools.ietf.org/html/rfc2198#section-3
payload_buffer[0] = ulpfec_payload_type_; // RED header.
memcpy(&payload_buffer[1], fec_packet->data.data(),
fec_packet->data.size());
total_fec_size_bytes += red_packet->size();
red_packet->set_packet_type(RtpPacketMediaType::kForwardErrorCorrection);
red_packet->set_allow_retransmission(false);
fec_packets.push_back(std::move(red_packet));
}
ResetState();
rtc::CritScope cs(&crit_);
fec_bitrate_.Update(total_fec_size_bytes, clock_->TimeInMilliseconds());
return fec_packets;
}
DataRate UlpfecGenerator::CurrentFecRate() const {
rtc::CritScope cs(&crit_);
return DataRate::BitsPerSec(
fec_bitrate_.Rate(clock_->TimeInMilliseconds()).value_or(0));
}
int UlpfecGenerator::Overhead() const {
RTC_DCHECK_RUNS_SERIALIZED(&race_checker_);
RTC_DCHECK(!media_packets_.empty());
int num_fec_packets =
fec_->NumFecPackets(media_packets_.size(), CurrentParams().fec_rate);
// Return the overhead in Q8.
return (num_fec_packets << 8) / media_packets_.size();
}
void UlpfecGenerator::ResetState() {
RTC_DCHECK_RUNS_SERIALIZED(&race_checker_);
media_packets_.clear();
last_media_packet_.reset();
generated_fec_packets_.clear();
num_protected_frames_ = 0;
}
} // namespace webrtc