| /* |
| * 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. |
| */ |
| |
| #include "webrtc/system_wrappers/include/rtp_to_ntp.h" |
| |
| #include "webrtc/system_wrappers/include/clock.h" |
| |
| #include <assert.h> |
| |
| namespace webrtc { |
| |
| RtcpMeasurement::RtcpMeasurement() |
| : ntp_secs(0), ntp_frac(0), rtp_timestamp(0) {} |
| |
| RtcpMeasurement::RtcpMeasurement(uint32_t ntp_secs, uint32_t ntp_frac, |
| uint32_t timestamp) |
| : ntp_secs(ntp_secs), ntp_frac(ntp_frac), rtp_timestamp(timestamp) {} |
| |
| // Calculates the RTP timestamp frequency from two pairs of NTP and RTP |
| // timestamps. |
| bool CalculateFrequency( |
| int64_t rtcp_ntp_ms1, |
| uint32_t rtp_timestamp1, |
| int64_t rtcp_ntp_ms2, |
| uint32_t rtp_timestamp2, |
| double* frequency_khz) { |
| if (rtcp_ntp_ms1 <= rtcp_ntp_ms2) { |
| return false; |
| } |
| *frequency_khz = static_cast<double>(rtp_timestamp1 - rtp_timestamp2) / |
| static_cast<double>(rtcp_ntp_ms1 - rtcp_ntp_ms2); |
| return true; |
| } |
| |
| // Detects if there has been a wraparound between |old_timestamp| and |
| // |new_timestamp|, and compensates by adding 2^32 if that is the case. |
| bool CompensateForWrapAround(uint32_t new_timestamp, |
| uint32_t old_timestamp, |
| int64_t* compensated_timestamp) { |
| assert(compensated_timestamp); |
| int64_t wraps = CheckForWrapArounds(new_timestamp, old_timestamp); |
| if (wraps < 0) { |
| // Reordering, don't use this packet. |
| return false; |
| } |
| *compensated_timestamp = new_timestamp + (wraps << 32); |
| return true; |
| } |
| |
| bool UpdateRtcpList(uint32_t ntp_secs, |
| uint32_t ntp_frac, |
| uint32_t rtp_timestamp, |
| RtcpList* rtcp_list, |
| bool* new_rtcp_sr) { |
| *new_rtcp_sr = false; |
| if (ntp_secs == 0 && ntp_frac == 0) { |
| return false; |
| } |
| |
| RtcpMeasurement measurement; |
| measurement.ntp_secs = ntp_secs; |
| measurement.ntp_frac = ntp_frac; |
| measurement.rtp_timestamp = rtp_timestamp; |
| |
| for (RtcpList::iterator it = rtcp_list->begin(); |
| it != rtcp_list->end(); ++it) { |
| if ((measurement.ntp_secs == (*it).ntp_secs && |
| measurement.ntp_frac == (*it).ntp_frac) || |
| (measurement.rtp_timestamp == (*it).rtp_timestamp)) { |
| // This RTCP has already been added to the list. |
| return true; |
| } |
| } |
| |
| // We need two RTCP SR reports to map between RTP and NTP. More than two will |
| // not improve the mapping. |
| if (rtcp_list->size() == 2) { |
| rtcp_list->pop_back(); |
| } |
| rtcp_list->push_front(measurement); |
| *new_rtcp_sr = true; |
| return true; |
| } |
| |
| // Converts |rtp_timestamp| to the NTP time base using the NTP and RTP timestamp |
| // pairs in |rtcp|. The converted timestamp is returned in |
| // |rtp_timestamp_in_ms|. This function compensates for wrap arounds in RTP |
| // timestamps and returns false if it can't do the conversion due to reordering. |
| bool RtpToNtpMs(int64_t rtp_timestamp, |
| const RtcpList& rtcp, |
| int64_t* rtp_timestamp_in_ms) { |
| if (rtcp.size() != 2) |
| return false; |
| |
| int64_t rtcp_ntp_ms_new = Clock::NtpToMs(rtcp.front().ntp_secs, |
| rtcp.front().ntp_frac); |
| int64_t rtcp_ntp_ms_old = Clock::NtpToMs(rtcp.back().ntp_secs, |
| rtcp.back().ntp_frac); |
| int64_t rtcp_timestamp_new = rtcp.front().rtp_timestamp; |
| int64_t rtcp_timestamp_old = rtcp.back().rtp_timestamp; |
| if (!CompensateForWrapAround(rtcp_timestamp_new, |
| rtcp_timestamp_old, |
| &rtcp_timestamp_new)) { |
| return false; |
| } |
| double freq_khz; |
| if (!CalculateFrequency(rtcp_ntp_ms_new, |
| rtcp_timestamp_new, |
| rtcp_ntp_ms_old, |
| rtcp_timestamp_old, |
| &freq_khz)) { |
| return false; |
| } |
| double offset = rtcp_timestamp_new - freq_khz * rtcp_ntp_ms_new; |
| int64_t rtp_timestamp_unwrapped; |
| if (!CompensateForWrapAround(rtp_timestamp, rtcp_timestamp_old, |
| &rtp_timestamp_unwrapped)) { |
| return false; |
| } |
| double rtp_timestamp_ntp_ms = (static_cast<double>(rtp_timestamp_unwrapped) - |
| offset) / freq_khz + 0.5f; |
| if (rtp_timestamp_ntp_ms < 0) { |
| return false; |
| } |
| *rtp_timestamp_in_ms = rtp_timestamp_ntp_ms; |
| return true; |
| } |
| |
| int CheckForWrapArounds(uint32_t new_timestamp, uint32_t old_timestamp) { |
| if (new_timestamp < old_timestamp) { |
| // This difference should be less than -2^31 if we have had a wrap around |
| // (e.g. |new_timestamp| = 1, |rtcp_rtp_timestamp| = 2^32 - 1). Since it is |
| // cast to a int32_t, it should be positive. |
| if (static_cast<int32_t>(new_timestamp - old_timestamp) > 0) { |
| // Forward wrap around. |
| return 1; |
| } |
| } else if (static_cast<int32_t>(old_timestamp - new_timestamp) > 0) { |
| // This difference should be less than -2^31 if we have had a backward wrap |
| // around. Since it is cast to a int32_t, it should be positive. |
| return -1; |
| } |
| return 0; |
| } |
| |
| } // namespace webrtc |