121 lines
4.8 KiB
C++
121 lines
4.8 KiB
C++
/*
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* Copyright (c) 2018 The WebRTC project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#include "call/receive_time_calculator.h"
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#include <memory>
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#include <string>
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#include <type_traits>
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#include "rtc_base/experiments/field_trial_parser.h"
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#include "rtc_base/numerics/safe_minmax.h"
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#include "system_wrappers/include/field_trial.h"
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namespace webrtc {
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namespace {
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using ::webrtc::field_trial::IsEnabled;
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const char kBweReceiveTimeCorrection[] = "WebRTC-Bwe-ReceiveTimeFix";
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} // namespace
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ReceiveTimeCalculatorConfig::ReceiveTimeCalculatorConfig()
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: max_packet_time_repair("maxrep", TimeDelta::Millis(2000)),
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stall_threshold("stall", TimeDelta::Millis(5)),
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tolerance("tol", TimeDelta::Millis(1)),
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max_stall("maxstall", TimeDelta::Seconds(5)) {
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std::string trial_string =
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field_trial::FindFullName(kBweReceiveTimeCorrection);
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ParseFieldTrial(
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{&max_packet_time_repair, &stall_threshold, &tolerance, &max_stall},
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trial_string);
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}
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ReceiveTimeCalculatorConfig::ReceiveTimeCalculatorConfig(
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const ReceiveTimeCalculatorConfig&) = default;
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ReceiveTimeCalculatorConfig::~ReceiveTimeCalculatorConfig() = default;
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ReceiveTimeCalculator::ReceiveTimeCalculator()
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: config_(ReceiveTimeCalculatorConfig()) {}
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std::unique_ptr<ReceiveTimeCalculator>
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ReceiveTimeCalculator::CreateFromFieldTrial() {
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if (!IsEnabled(kBweReceiveTimeCorrection))
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return nullptr;
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return std::make_unique<ReceiveTimeCalculator>();
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}
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int64_t ReceiveTimeCalculator::ReconcileReceiveTimes(int64_t packet_time_us,
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int64_t system_time_us,
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int64_t safe_time_us) {
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int64_t stall_time_us = system_time_us - packet_time_us;
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if (total_system_time_passed_us_ < config_.stall_threshold->us()) {
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stall_time_us = rtc::SafeMin(stall_time_us, config_.max_stall->us());
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}
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int64_t corrected_time_us = safe_time_us - stall_time_us;
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if (last_packet_time_us_ == -1 && stall_time_us < 0) {
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static_clock_offset_us_ = stall_time_us;
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corrected_time_us += static_clock_offset_us_;
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} else if (last_packet_time_us_ > 0) {
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// All repairs depend on variables being intialized
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int64_t packet_time_delta_us = packet_time_us - last_packet_time_us_;
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int64_t system_time_delta_us = system_time_us - last_system_time_us_;
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int64_t safe_time_delta_us = safe_time_us - last_safe_time_us_;
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// Repair backwards clock resets during initial stall. In this case, the
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// reset is observed only in packet time but never in system time.
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if (system_time_delta_us < 0)
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total_system_time_passed_us_ += config_.stall_threshold->us();
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else
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total_system_time_passed_us_ += system_time_delta_us;
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if (packet_time_delta_us < 0 &&
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total_system_time_passed_us_ < config_.stall_threshold->us()) {
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static_clock_offset_us_ -= packet_time_delta_us;
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}
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corrected_time_us += static_clock_offset_us_;
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// Detect resets inbetween clock readings in socket and app.
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bool forward_clock_reset =
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corrected_time_us + config_.tolerance->us() < last_corrected_time_us_;
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bool obvious_backward_clock_reset = system_time_us < packet_time_us;
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// Harder case with backward clock reset during stall, the reset being
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// smaller than the stall. Compensate throughout the stall.
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bool small_backward_clock_reset =
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!obvious_backward_clock_reset &&
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safe_time_delta_us > system_time_delta_us + config_.tolerance->us();
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bool stall_start =
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packet_time_delta_us >= 0 &&
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system_time_delta_us > packet_time_delta_us + config_.tolerance->us();
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bool stall_is_over = safe_time_delta_us > config_.stall_threshold->us();
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bool packet_time_caught_up =
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packet_time_delta_us < 0 && system_time_delta_us >= 0;
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if (stall_start && small_backward_clock_reset)
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small_reset_during_stall_ = true;
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else if (stall_is_over || packet_time_caught_up)
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small_reset_during_stall_ = false;
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// If resets are detected, advance time by (capped) packet time increase.
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if (forward_clock_reset || obvious_backward_clock_reset ||
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small_reset_during_stall_) {
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corrected_time_us = last_corrected_time_us_ +
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rtc::SafeClamp(packet_time_delta_us, 0,
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config_.max_packet_time_repair->us());
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}
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}
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last_corrected_time_us_ = corrected_time_us;
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last_packet_time_us_ = packet_time_us;
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last_system_time_us_ = system_time_us;
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last_safe_time_us_ = safe_time_us;
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return corrected_time_us;
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}
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} // namespace webrtc
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