1 /* 2 * Copyright (c) 2012 The WebRTC project authors. All Rights Reserved. 3 * 4 * Use of this source code is governed by a BSD-style license 5 * that can be found in the LICENSE file in the root of the source 6 * tree. An additional intellectual property rights grant can be found 7 * in the file PATENTS. All contributing project authors may 8 * be found in the AUTHORS file in the root of the source tree. 9 */ 10 11 #include "webrtc/system_wrappers/interface/rtp_to_ntp.h" 12 13 #include "webrtc/system_wrappers/interface/clock.h" 14 15 #include <assert.h> 16 17 namespace webrtc { 18 19 RtcpMeasurement::RtcpMeasurement() 20 : ntp_secs(0), ntp_frac(0), rtp_timestamp(0) {} 21 22 RtcpMeasurement::RtcpMeasurement(uint32_t ntp_secs, uint32_t ntp_frac, 23 uint32_t timestamp) 24 : ntp_secs(ntp_secs), ntp_frac(ntp_frac), rtp_timestamp(timestamp) {} 25 26 // Calculates the RTP timestamp frequency from two pairs of NTP and RTP 27 // timestamps. 28 bool CalculateFrequency( 29 int64_t rtcp_ntp_ms1, 30 uint32_t rtp_timestamp1, 31 int64_t rtcp_ntp_ms2, 32 uint32_t rtp_timestamp2, 33 double* frequency_khz) { 34 if (rtcp_ntp_ms1 <= rtcp_ntp_ms2) { 35 return false; 36 } 37 *frequency_khz = static_cast<double>(rtp_timestamp1 - rtp_timestamp2) / 38 static_cast<double>(rtcp_ntp_ms1 - rtcp_ntp_ms2); 39 return true; 40 } 41 42 // Detects if there has been a wraparound between |old_timestamp| and 43 // |new_timestamp|, and compensates by adding 2^32 if that is the case. 44 bool CompensateForWrapAround(uint32_t new_timestamp, 45 uint32_t old_timestamp, 46 int64_t* compensated_timestamp) { 47 assert(compensated_timestamp); 48 int64_t wraps = CheckForWrapArounds(new_timestamp, old_timestamp); 49 if (wraps < 0) { 50 // Reordering, don't use this packet. 51 return false; 52 } 53 *compensated_timestamp = new_timestamp + (wraps << 32); 54 return true; 55 } 56 57 bool UpdateRtcpList(uint32_t ntp_secs, 58 uint32_t ntp_frac, 59 uint32_t rtp_timestamp, 60 RtcpList* rtcp_list, 61 bool* new_rtcp_sr) { 62 *new_rtcp_sr = false; 63 if (ntp_secs == 0 && ntp_frac == 0) { 64 return false; 65 } 66 67 RtcpMeasurement measurement; 68 measurement.ntp_secs = ntp_secs; 69 measurement.ntp_frac = ntp_frac; 70 measurement.rtp_timestamp = rtp_timestamp; 71 72 for (RtcpList::iterator it = rtcp_list->begin(); 73 it != rtcp_list->end(); ++it) { 74 if (measurement.ntp_secs == (*it).ntp_secs && 75 measurement.ntp_frac == (*it).ntp_frac) { 76 // This RTCP has already been added to the list. 77 return true; 78 } 79 } 80 81 // We need two RTCP SR reports to map between RTP and NTP. More than two will 82 // not improve the mapping. 83 if (rtcp_list->size() == 2) { 84 rtcp_list->pop_back(); 85 } 86 rtcp_list->push_front(measurement); 87 *new_rtcp_sr = true; 88 return true; 89 } 90 91 // Converts |rtp_timestamp| to the NTP time base using the NTP and RTP timestamp 92 // pairs in |rtcp|. The converted timestamp is returned in 93 // |rtp_timestamp_in_ms|. This function compensates for wrap arounds in RTP 94 // timestamps and returns false if it can't do the conversion due to reordering. 95 bool RtpToNtpMs(int64_t rtp_timestamp, 96 const RtcpList& rtcp, 97 int64_t* rtp_timestamp_in_ms) { 98 assert(rtcp.size() == 2); 99 int64_t rtcp_ntp_ms_new = Clock::NtpToMs(rtcp.front().ntp_secs, 100 rtcp.front().ntp_frac); 101 int64_t rtcp_ntp_ms_old = Clock::NtpToMs(rtcp.back().ntp_secs, 102 rtcp.back().ntp_frac); 103 int64_t rtcp_timestamp_new = rtcp.front().rtp_timestamp; 104 int64_t rtcp_timestamp_old = rtcp.back().rtp_timestamp; 105 if (!CompensateForWrapAround(rtcp_timestamp_new, 106 rtcp_timestamp_old, 107 &rtcp_timestamp_new)) { 108 return false; 109 } 110 double freq_khz; 111 if (!CalculateFrequency(rtcp_ntp_ms_new, 112 rtcp_timestamp_new, 113 rtcp_ntp_ms_old, 114 rtcp_timestamp_old, 115 &freq_khz)) { 116 return false; 117 } 118 double offset = rtcp_timestamp_new - freq_khz * rtcp_ntp_ms_new; 119 int64_t rtp_timestamp_unwrapped; 120 if (!CompensateForWrapAround(rtp_timestamp, rtcp_timestamp_old, 121 &rtp_timestamp_unwrapped)) { 122 return false; 123 } 124 double rtp_timestamp_ntp_ms = (static_cast<double>(rtp_timestamp_unwrapped) - 125 offset) / freq_khz + 0.5f; 126 if (rtp_timestamp_ntp_ms < 0) { 127 return false; 128 } 129 *rtp_timestamp_in_ms = rtp_timestamp_ntp_ms; 130 return true; 131 } 132 133 int CheckForWrapArounds(uint32_t new_timestamp, uint32_t old_timestamp) { 134 if (new_timestamp < old_timestamp) { 135 // This difference should be less than -2^31 if we have had a wrap around 136 // (e.g. |new_timestamp| = 1, |rtcp_rtp_timestamp| = 2^32 - 1). Since it is 137 // cast to a int32_t, it should be positive. 138 if (static_cast<int32_t>(new_timestamp - old_timestamp) > 0) { 139 // Forward wrap around. 140 return 1; 141 } 142 } else if (static_cast<int32_t>(old_timestamp - new_timestamp) > 0) { 143 // This difference should be less than -2^31 if we have had a backward wrap 144 // around. Since it is cast to a int32_t, it should be positive. 145 return -1; 146 } 147 return 0; 148 } 149 150 } // namespace webrtc 151
