webrtc/modules/rtp_rtcp/source/remote_ntp_time_estimator.cc

/*
 *  Copyright (c) 2014 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 "webrtc/modules/rtp_rtcp/interface/remote_ntp_time_estimator.h"

#include "webrtc/modules/rtp_rtcp/interface/rtp_rtcp.h"
#include "webrtc/system_wrappers/interface/clock.h"
#include "webrtc/system_wrappers/interface/timestamp_extrapolator.h"

namespace webrtc {

// TODO(wu): Refactor this class so that it can be shared with
// vie_sync_module.cc.
RemoteNtpTimeEstimator::RemoteNtpTimeEstimator(Clock* clock)
    : clock_(clock),
      ts_extrapolator_(
          new TimestampExtrapolator(clock_->TimeInMilliseconds())) {
}

RemoteNtpTimeEstimator::~RemoteNtpTimeEstimator() {}

bool RemoteNtpTimeEstimator::UpdateRtcpTimestamp(uint32_t ssrc,
                                                 RtpRtcp* rtp_rtcp) {
  assert(rtp_rtcp);
  uint16_t rtt = 0;
  rtp_rtcp->RTT(ssrc, &rtt, NULL, NULL, NULL);
  if (rtt == 0) {
    // Waiting for valid rtt.
    return true;
  }
  // Update RTCP list
  uint32_t ntp_secs = 0;
  uint32_t ntp_frac = 0;
  uint32_t rtp_timestamp = 0;
  if (0 != rtp_rtcp->RemoteNTP(&ntp_secs,
                               &ntp_frac,
                               NULL,
                               NULL,
                               &rtp_timestamp)) {
    // Waiting for RTCP.
    return true;
  }
  bool new_rtcp_sr = false;
  if (!UpdateRtcpList(
      ntp_secs, ntp_frac, rtp_timestamp, &rtcp_list_, &new_rtcp_sr)) {
    return false;
  }
  if (!new_rtcp_sr) {
    // No new RTCP SR since last time this function was called.
    return true;
  }
  // Update extrapolator with the new arrival time.
  // The extrapolator assumes the TimeInMilliseconds time.
  int64_t receiver_arrival_time_ms = clock_->TimeInMilliseconds();
  int64_t sender_send_time_ms = Clock::NtpToMs(ntp_secs, ntp_frac);
  int64_t sender_arrival_time_90k = (sender_send_time_ms + rtt / 2) * 90;
  ts_extrapolator_->Update(receiver_arrival_time_ms, sender_arrival_time_90k);
  return true;
}

int64_t RemoteNtpTimeEstimator::Estimate(uint32_t rtp_timestamp) {
  if (rtcp_list_.size() < 2) {
    // We need two RTCP SR reports to calculate NTP.
    return -1;
  }
  int64_t sender_capture_ntp_ms = 0;
  if (!RtpToNtpMs(rtp_timestamp, rtcp_list_, &sender_capture_ntp_ms)) {
    return -1;
  }
  uint32_t timestamp = sender_capture_ntp_ms * 90;
  int64_t receiver_capture_ms =
      ts_extrapolator_->ExtrapolateLocalTime(timestamp);
  int64_t ntp_offset =
      clock_->CurrentNtpInMilliseconds() - clock_->TimeInMilliseconds();
  return receiver_capture_ms + ntp_offset;
}

}  // namespace webrtc