rtt calculation handles time go backwards

webrtc/modules/rtp_rtcp/source/time_util.h

 /*
  *  Copyright (c) 2015 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.
  */
 
@@ skipping 21 matching lines @@
 // Wallclock time is represented using the timestamp format of
 // the Network Time Protocol (NTP).
 // ...
 // In some fields where a more compact representation is
 // appropriate, only the middle 32 bits are used; that is, the low 16
 // bits of the integer part and the high 16 bits of the fractional part.
 inline uint32_t CompactNtp(NtpTime ntp) {
   return (ntp.seconds() << 16) | (ntp.fractions() >> 16);
 }
 // Converts interval between compact ntp timestamps to milliseconds.
-// This interval can be upto ~18.2 hours (2^16 seconds).
-inline uint32_t CompactNtpIntervalToMs(uint32_t compact_ntp_interval) {
-  uint64_t value = static_cast<uint64_t>(compact_ntp_interval);
-  return (value * 1000 + (1 << 15)) >> 16;
-}
+// This interval can be up to ~9.1 hours (2^15 seconds).
+// Values close to 2^16 seconds consider negative and result in minimum rtt = 1.
+int64_t CompactNtpRttToMs(uint32_t compact_ntp_interval);
 
 }  // namespace webrtc
 #endif  // WEBRTC_MODULES_RTP_RTCP_SOURCE_TIME_UTIL_H_