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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 RTC_BASE_RTP_TO_NTP_ESTIMATOR_H_
#define RTC_BASE_RTP_TO_NTP_ESTIMATOR_H_
#include <cstdint>
#include <list>
#include <optional>
#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 // RTC_BASE_RTP_TO_NTP_ESTIMATOR_H_
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