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/*
* Copyright (c) 2018 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 "call/receive_time_calculator.h"
#include <memory>
#include <string>
#include <type_traits>
#include "rtc_base/experiments/field_trial_parser.h"
#include "rtc_base/numerics/safe_minmax.h"
namespace webrtc {
namespace {
const char kBweReceiveTimeCorrection[] = "WebRTC-Bwe-ReceiveTimeFix";
} // namespace
ReceiveTimeCalculatorConfig::ReceiveTimeCalculatorConfig(
const FieldTrialsView& field_trials)
: max_packet_time_repair("maxrep", TimeDelta::Millis(2000)),
stall_threshold("stall", TimeDelta::Millis(5)),
tolerance("tol", TimeDelta::Millis(1)),
max_stall("maxstall", TimeDelta::Seconds(5)) {
std::string trial_string = field_trials.Lookup(kBweReceiveTimeCorrection);
ParseFieldTrial(
{&max_packet_time_repair, &stall_threshold, &tolerance, &max_stall},
trial_string);
}
ReceiveTimeCalculatorConfig::ReceiveTimeCalculatorConfig(
const ReceiveTimeCalculatorConfig&) = default;
ReceiveTimeCalculatorConfig::~ReceiveTimeCalculatorConfig() = default;
ReceiveTimeCalculator::ReceiveTimeCalculator(
const FieldTrialsView& field_trials)
: config_(field_trials) {}
std::unique_ptr<ReceiveTimeCalculator>
ReceiveTimeCalculator::CreateFromFieldTrial(
const FieldTrialsView& field_trials) {
if (!field_trials.IsEnabled(kBweReceiveTimeCorrection))
return nullptr;
return std::make_unique<ReceiveTimeCalculator>(field_trials);
}
int64_t ReceiveTimeCalculator::ReconcileReceiveTimes(int64_t packet_time_us,
int64_t system_time_us,
int64_t safe_time_us) {
int64_t stall_time_us = system_time_us - packet_time_us;
if (total_system_time_passed_us_ < config_.stall_threshold->us()) {
stall_time_us = rtc::SafeMin(stall_time_us, config_.max_stall->us());
}
int64_t corrected_time_us = safe_time_us - stall_time_us;
if (last_packet_time_us_ == -1 && stall_time_us < 0) {
static_clock_offset_us_ = stall_time_us;
corrected_time_us += static_clock_offset_us_;
} else if (last_packet_time_us_ > 0) {
// All repairs depend on variables being intialized
int64_t packet_time_delta_us = packet_time_us - last_packet_time_us_;
int64_t system_time_delta_us = system_time_us - last_system_time_us_;
int64_t safe_time_delta_us = safe_time_us - last_safe_time_us_;
// Repair backwards clock resets during initial stall. In this case, the
// reset is observed only in packet time but never in system time.
if (system_time_delta_us < 0)
total_system_time_passed_us_ += config_.stall_threshold->us();
else
total_system_time_passed_us_ += system_time_delta_us;
if (packet_time_delta_us < 0 &&
total_system_time_passed_us_ < config_.stall_threshold->us()) {
static_clock_offset_us_ -= packet_time_delta_us;
}
corrected_time_us += static_clock_offset_us_;
// Detect resets inbetween clock readings in socket and app.
bool forward_clock_reset =
corrected_time_us + config_.tolerance->us() < last_corrected_time_us_;
bool obvious_backward_clock_reset = system_time_us < packet_time_us;
// Harder case with backward clock reset during stall, the reset being
// smaller than the stall. Compensate throughout the stall.
bool small_backward_clock_reset =
!obvious_backward_clock_reset &&
safe_time_delta_us > system_time_delta_us + config_.tolerance->us();
bool stall_start =
packet_time_delta_us >= 0 &&
system_time_delta_us > packet_time_delta_us + config_.tolerance->us();
bool stall_is_over = safe_time_delta_us > config_.stall_threshold->us();
bool packet_time_caught_up =
packet_time_delta_us < 0 && system_time_delta_us >= 0;
if (stall_start && small_backward_clock_reset)
small_reset_during_stall_ = true;
else if (stall_is_over || packet_time_caught_up)
small_reset_during_stall_ = false;
// If resets are detected, advance time by (capped) packet time increase.
if (forward_clock_reset || obvious_backward_clock_reset ||
small_reset_during_stall_) {
corrected_time_us = last_corrected_time_us_ +
rtc::SafeClamp(packet_time_delta_us, 0,
config_.max_packet_time_repair->us());
}
}
last_corrected_time_us_ = corrected_time_us;
last_packet_time_us_ = packet_time_us;
last_system_time_us_ = system_time_us;
last_safe_time_us_ = safe_time_us;
return corrected_time_us;
}
} // namespace webrtc
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