blob: 3496fc07244d94b2709302d63bcf20afdb7e32de [file] [log] [blame]
/*
* 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 "system_wrappers/include/rtp_to_ntp_estimator.h"
#include "rtc_base/checks.h"
#include "rtc_base/logging.h"
#include "system_wrappers/include/clock.h"
namespace webrtc {
namespace {
// Number of RTCP SR reports to use to map between RTP and NTP.
const size_t kNumRtcpReportsToUse = 2;
// Calculates the RTP timestamp frequency from two pairs of NTP/RTP timestamps.
bool CalculateFrequency(int64_t ntp_ms1,
uint32_t rtp_timestamp1,
int64_t ntp_ms2,
uint32_t rtp_timestamp2,
double* frequency_khz) {
if (ntp_ms1 <= ntp_ms2)
return false;
*frequency_khz = static_cast<double>(rtp_timestamp1 - rtp_timestamp2) /
static_cast<double>(ntp_ms1 - ntp_ms2);
return true;
}
// Detects if there has been a wraparound between |old_timestamp| and
// |new_timestamp|, and compensates by adding 2^32 if that is the case.
bool CompensateForWrapAround(uint32_t new_timestamp,
uint32_t old_timestamp,
int64_t* compensated_timestamp) {
int64_t wraps = CheckForWrapArounds(new_timestamp, old_timestamp);
if (wraps < 0) {
// Reordering, don't use this packet.
return false;
}
*compensated_timestamp = new_timestamp + (wraps << 32);
return true;
}
bool Contains(const std::list<RtpToNtpEstimator::RtcpMeasurement>& measurements,
const RtpToNtpEstimator::RtcpMeasurement& other) {
for (const auto& measurement : measurements) {
if (measurement.IsEqual(other))
return true;
}
return false;
}
} // namespace
RtpToNtpEstimator::RtcpMeasurement::RtcpMeasurement(uint32_t ntp_secs,
uint32_t ntp_frac,
uint32_t timestamp)
: ntp_time(ntp_secs, ntp_frac), rtp_timestamp(timestamp) {}
bool RtpToNtpEstimator::RtcpMeasurement::IsEqual(
const RtcpMeasurement& other) const {
// Use || since two equal timestamps will result in zero frequency and in
// RtpToNtpMs, |rtp_timestamp_ms| is estimated by dividing by the frequency.
return (ntp_time == other.ntp_time) || (rtp_timestamp == other.rtp_timestamp);
}
// Class for converting an RTP timestamp to the NTP domain.
RtpToNtpEstimator::RtpToNtpEstimator() : consecutive_invalid_samples_(0) {}
RtpToNtpEstimator::~RtpToNtpEstimator() {}
void RtpToNtpEstimator::UpdateParameters() {
if (measurements_.size() != kNumRtcpReportsToUse)
return;
int64_t timestamp_new = measurements_.front().rtp_timestamp;
int64_t timestamp_old = measurements_.back().rtp_timestamp;
if (!CompensateForWrapAround(timestamp_new, timestamp_old, &timestamp_new))
return;
int64_t ntp_ms_new = measurements_.front().ntp_time.ToMs();
int64_t ntp_ms_old = measurements_.back().ntp_time.ToMs();
if (!CalculateFrequency(ntp_ms_new, timestamp_new, ntp_ms_old, timestamp_old,
&params_.frequency_khz)) {
return;
}
params_.offset_ms = timestamp_new - params_.frequency_khz * ntp_ms_new;
params_.calculated = true;
}
bool RtpToNtpEstimator::UpdateMeasurements(uint32_t ntp_secs,
uint32_t ntp_frac,
uint32_t rtp_timestamp,
bool* new_rtcp_sr) {
*new_rtcp_sr = false;
RtcpMeasurement new_measurement(ntp_secs, ntp_frac, rtp_timestamp);
if (Contains(measurements_, new_measurement)) {
// RTCP SR report already added.
return true;
}
if (!new_measurement.ntp_time.Valid())
return false;
int64_t ntp_ms_new = new_measurement.ntp_time.ToMs();
bool invalid_sample = false;
for (const auto& measurement : measurements_) {
if (ntp_ms_new <= measurement.ntp_time.ToMs()) {
// Old report.
invalid_sample = true;
break;
}
int64_t timestamp_new = new_measurement.rtp_timestamp;
if (!CompensateForWrapAround(timestamp_new, measurement.rtp_timestamp,
&timestamp_new)) {
invalid_sample = true;
break;
}
if (timestamp_new <= measurement.rtp_timestamp) {
LOG(LS_WARNING)
<< "Newer RTCP SR report with older RTP timestamp, dropping";
invalid_sample = true;
break;
}
}
if (invalid_sample) {
++consecutive_invalid_samples_;
if (consecutive_invalid_samples_ < kMaxInvalidSamples) {
return false;
}
LOG(LS_WARNING) << "Multiple consecutively invalid RTCP SR reports, "
"clearing measurements.";
measurements_.clear();
}
consecutive_invalid_samples_ = 0;
// Insert new RTCP SR report.
if (measurements_.size() == kNumRtcpReportsToUse)
measurements_.pop_back();
measurements_.push_front(new_measurement);
*new_rtcp_sr = true;
// List updated, calculate new parameters.
UpdateParameters();
return true;
}
bool RtpToNtpEstimator::Estimate(int64_t rtp_timestamp,
int64_t* rtp_timestamp_ms) const {
if (!params_.calculated || measurements_.empty())
return false;
uint32_t rtp_timestamp_old = measurements_.back().rtp_timestamp;
int64_t rtp_timestamp_unwrapped;
if (!CompensateForWrapAround(rtp_timestamp, rtp_timestamp_old,
&rtp_timestamp_unwrapped)) {
return false;
}
// params_.calculated should not be true unless params_.frequency_khz has been
// set to something non-zero.
RTC_DCHECK_NE(params_.frequency_khz, 0.0);
double rtp_ms =
(static_cast<double>(rtp_timestamp_unwrapped) - params_.offset_ms) /
params_.frequency_khz +
0.5f;
if (rtp_ms < 0)
return false;
*rtp_timestamp_ms = rtp_ms;
return true;
}
int CheckForWrapArounds(uint32_t new_timestamp, uint32_t old_timestamp) {
if (new_timestamp < old_timestamp) {
// This difference should be less than -2^31 if we have had a wrap around
// (e.g. |new_timestamp| = 1, |rtcp_rtp_timestamp| = 2^32 - 1). Since it is
// cast to a int32_t, it should be positive.
if (static_cast<int32_t>(new_timestamp - old_timestamp) > 0) {
// Forward wrap around.
return 1;
}
} else if (static_cast<int32_t>(old_timestamp - new_timestamp) > 0) {
// This difference should be less than -2^31 if we have had a backward wrap
// around. Since it is cast to a int32_t, it should be positive.
return -1;
}
return 0;
}
} // namespace webrtc