system_wrappers/source/rtp_to_ntp_estimator.cc

/*
 *  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;
// Number of parameters samples used to smooth.
const size_t kNumSamplesToSmooth = 20;

// 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;
}

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

bool RtpToNtpEstimator::Parameters::operator<(const Parameters& other) const {
  if (frequency_khz < other.frequency_khz - 1e-6) {
    return true;
  } else if (frequency_khz > other.frequency_khz + 1e-6) {
    return false;
  } else {
    return offset_ms < other.offset_ms - 1e-6;
  }
}

bool RtpToNtpEstimator::Parameters::operator==(const Parameters& other) const {
  return !(other < *this || *this < other);
}

bool RtpToNtpEstimator::Parameters::operator!=(const Parameters& other) const {
  return other < *this || *this < other;
}

bool RtpToNtpEstimator::Parameters::operator<=(const Parameters& other) const {
  return !(other < *this);
}

RtpToNtpEstimator::RtcpMeasurement::RtcpMeasurement(uint32_t ntp_secs,
                                                    uint32_t ntp_frac,
                                                    int64_t unwrapped_timestamp)
    : ntp_time(ntp_secs, ntp_frac),
      unwrapped_rtp_timestamp(unwrapped_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) ||
         (unwrapped_rtp_timestamp == other.unwrapped_rtp_timestamp);
}

// Class for converting an RTP timestamp to the NTP domain.
RtpToNtpEstimator::RtpToNtpEstimator()
    : consecutive_invalid_samples_(0),
      smoothing_filter_(kNumSamplesToSmooth),
      params_calculated_(false) {}

RtpToNtpEstimator::~RtpToNtpEstimator() {}

void RtpToNtpEstimator::UpdateParameters() {
  if (measurements_.size() != kNumRtcpReportsToUse)
    return;

  Parameters params;
  int64_t timestamp_new = measurements_.front().unwrapped_rtp_timestamp;
  int64_t timestamp_old = measurements_.back().unwrapped_rtp_timestamp;

  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;
  smoothing_filter_.Insert(params);
}

bool RtpToNtpEstimator::UpdateMeasurements(uint32_t ntp_secs,
                                           uint32_t ntp_frac,
                                           uint32_t rtp_timestamp,
                                           bool* new_rtcp_sr) {
  *new_rtcp_sr = false;

  int64_t unwrapped_rtp_timestamp = unwrapper_.Unwrap(rtp_timestamp);

  RtcpMeasurement new_measurement(ntp_secs, ntp_frac, unwrapped_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;
  if (!measurements_.empty()) {
    int64_t old_rtp_timestamp = measurements_.front().unwrapped_rtp_timestamp;
    int64_t old_ntp_ms = measurements_.front().ntp_time.ToMs();
    if (ntp_ms_new <= old_ntp_ms) {
      invalid_sample = true;
    } else if (unwrapped_rtp_timestamp <= old_rtp_timestamp) {
      RTC_LOG(LS_WARNING)
          << "Newer RTCP SR report with older RTP timestamp, dropping";
      invalid_sample = true;
    } else if (unwrapped_rtp_timestamp - old_rtp_timestamp > (1 << 25)) {
      // Sanity check. No jumps too far into the future in rtp.
      invalid_sample = true;
    }
  }

  if (invalid_sample) {
    ++consecutive_invalid_samples_;
    if (consecutive_invalid_samples_ < kMaxInvalidSamples) {
      return false;
    }
    RTC_LOG(LS_WARNING) << "Multiple consecutively invalid RTCP SR reports, "
                           "clearing measurements.";
    measurements_.clear();
    smoothing_filter_.Reset();
    params_calculated_ = false;
  }
  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_)
    return false;

  int64_t rtp_timestamp_unwrapped = unwrapper_.Unwrap(rtp_timestamp);

  Parameters params = smoothing_filter_.GetFilteredValue();

  // params_calculated_ should not be true unless ms params.frequency_khz has
  // been calculated 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;
}

const absl::optional<RtpToNtpEstimator::Parameters> RtpToNtpEstimator::params()
    const {
  absl::optional<Parameters> res;
  if (params_calculated_) {
    res.emplace(smoothing_filter_.GetFilteredValue());
  }
  return res;
}
}  // namespace webrtc