rtp_to_ntp_estimator.h

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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.

*/

#ifndef SYSTEM_WRAPPERS_INCLUDE_RTP_TO_NTP_ESTIMATOR_H_

#define SYSTEM_WRAPPERS_INCLUDE_RTP_TO_NTP_ESTIMATOR_H_

#include <stdint.h>

#include <list>

#include <optional>

#include "rtc_base/checks.h"

#include "rtc_base/numerics/sequence_number_unwrapper.h"

#include "system_wrappers/include/ntp_time.h"

namespace webrtc {

// Converts an RTP timestamp to the NTP domain.

// The class needs to be trained with (at least 2) RTP/NTP timestamp pairs from

// RTCP sender reports before the convertion can be done.

class RtpToNtpEstimator {

 public:

  static constexpr int kMaxInvalidSamples = 3;

  RtpToNtpEstimator() = default;

  RtpToNtpEstimator(const RtpToNtpEstimator&) = delete;

  RtpToNtpEstimator& operator=(const RtpToNtpEstimator&) = delete;

  ~RtpToNtpEstimator() = default;

  enum UpdateResult { kInvalidMeasurement, kSameMeasurement, kNewMeasurement };

  // Updates measurements with RTP/NTP timestamp pair from a RTCP sender report.

  UpdateResult UpdateMeasurements(NtpTime ntp, uint32_t rtp_timestamp);

  // Converts an RTP timestamp to the NTP domain.

  // Returns invalid NtpTime (i.e. NtpTime(0)) on failure.

  NtpTime Estimate(uint32_t rtp_timestamp) const;

  // Returns estimated rtp_timestamp frequency, or 0 on failure.

  double EstimatedFrequencyKhz() const;

 private:

  // Estimated parameters from RTP and NTP timestamp pairs in `measurements_`.

  // Defines linear estimation: NtpTime (in units of 1s/2^32) =

  //   `Parameters::slope` * rtp_timestamp + `Parameters::offset`.

  struct Parameters {

    double slope;

    double offset;

};

  // RTP and NTP timestamp pair from a RTCP SR report.

  struct RtcpMeasurement {

    NtpTime ntp_time;

    int64_t unwrapped_rtp_timestamp;

};

  void UpdateParameters();

  int consecutive_invalid_samples_ = 0;

  std::list<RtcpMeasurement> measurements_;

  std::optional<Parameters> params_;

  mutable RtpTimestampUnwrapper unwrapper_;

};

}  // namespace webrtc

#endif  // SYSTEM_WRAPPERS_INCLUDE_RTP_TO_NTP_ESTIMATOR_H_