/* * Copyright (c) 2016 The ZLMediaKit project authors. All Rights Reserved. * * This file is part of ZLMediaKit(https://github.com/xia-chu/ZLMediaKit). * * Use of this source code is governed by MIT license that can be found in the * LICENSE file in the root of the source tree. All contributing project authors * may be found in the AUTHORS file in the root of the source tree. */ #include "Stamp.h" #define MAX_DELTA_STAMP 1000 #define MAX_CTS 500 #define ABS(x) ((x) > 0 ? (x) : (-x)) namespace mediakit { int64_t DeltaStamp::deltaStamp(int64_t stamp) { if(!_last_stamp){ //第一次计算时间戳增量,时间戳增量为0 if(stamp){ _last_stamp = stamp; } return 0; } int64_t ret = stamp - _last_stamp; if(ret >= 0){ //时间戳增量为正，返回之 _last_stamp = stamp; //在直播情况下，时间戳增量不得大于MAX_DELTA_STAMP return ret < MAX_DELTA_STAMP ? ret : 0; } //时间戳增量为负，说明时间戳回环了或回退了 _last_stamp = stamp; //如果时间戳回退不多，那么返回负值 return -ret < MAX_CTS ? ret : 0; } void Stamp::setPlayBack(bool playback) { _playback = playback; } void Stamp::syncTo(Stamp &other){ _sync_master = &other; } //限制dts回退 void Stamp::revise(int64_t dts, int64_t pts, int64_t &dts_out, int64_t &pts_out,bool modifyStamp) { revise_l(dts, pts, dts_out, pts_out, modifyStamp); if (_playback) { //回放允许时间戳回退 return; } if (dts_out < _last_dts_out) { // WarnL << "dts回退:" << dts_out << " < " << _last_dts_out; dts_out = _last_dts_out; pts_out = _last_pts_out; return; } _last_dts_out = dts_out; _last_pts_out = pts_out; } //音视频时间戳同步 void Stamp::revise_l(int64_t dts, int64_t pts, int64_t &dts_out, int64_t &pts_out,bool modifyStamp) { revise_l2(dts, pts, dts_out, pts_out, modifyStamp); if (!_sync_master || modifyStamp || _playback) { //自动生成时间戳或回放或同步完毕 return; } if (_sync_master && _sync_master->_last_dts_in) { //音视频dts当前时间差 int64_t dts_diff = _last_dts_in - _sync_master->_last_dts_in; if (ABS(dts_diff) < 5000) { //如果绝对时间戳小于5秒，那么说明他们的起始时间戳是一致的，那么强制同步 _relative_stamp = _sync_master->_relative_stamp + dts_diff; } //下次不用再强制同步 _sync_master = nullptr; } } //求取相对时间戳 void Stamp::revise_l2(int64_t dts, int64_t pts, int64_t &dts_out, int64_t &pts_out,bool modifyStamp) { if (!pts) { //没有播放时间戳,使其赋值为解码时间戳 pts = dts; } if (_playback) { //这是点播 dts_out = dts; pts_out = pts; _relative_stamp = dts_out; _last_dts_in = dts; return; } //pts和dts的差值 int64_t pts_dts_diff = pts - dts; if (_last_dts_in != dts) { //时间戳发生变更 if (modifyStamp) { //内部自己生产时间戳 _relative_stamp = _ticker.elapsedTime(); } else { _relative_stamp += deltaStamp(dts); } _last_dts_in = dts; } dts_out = _relative_stamp; //////////////以下是播放时间戳的计算////////////////// if (ABS(pts_dts_diff) > MAX_CTS) { //如果差值太大，则认为由于回环导致时间戳错乱了 pts_dts_diff = 0; } pts_out = dts_out + pts_dts_diff; } void Stamp::setRelativeStamp(int64_t relativeStamp) { _relative_stamp = relativeStamp; } int64_t Stamp::getRelativeStamp() const { return _relative_stamp; } bool DtsGenerator::getDts(uint32_t pts, uint32_t &dts){ bool ret = false; if (pts == _last_pts) { //pts未变，说明dts也不会变，返回上次dts if (_last_dts) { dts = _last_dts; ret = true; } } else { //pts变了，尝试计算dts ret = getDts_l(pts, dts); if (ret) { //获取到了dts，保存本次结果 _last_dts = dts; } } if (!ret) { //pts排序列队长度还不知道，也就是不知道有没有B帧， //那么先强制dts == pts，这样可能导致有B帧的情况下，起始画面有几帧回退 dts = pts; } //记录上次pts _last_pts = pts; return ret; } //该算法核心思想是对pts进行排序，排序好的pts就是dts。 //排序有一定的滞后性，那么需要加上排序导致的时间戳偏移量 bool DtsGenerator::getDts_l(uint32_t pts, uint32_t &dts){ if(_sorter_max_size == 1){ //没有B帧，dts就等于pts dts = pts; return true; } if(!_sorter_max_size){ //尚未计算出pts排序列队长度(也就是P帧间B帧个数) if(pts > _last_max_pts){ //pts时间戳增加了，那么说明这帧画面不是B帧(说明是P帧或关键帧) if(_frames_since_last_max_pts && _count_sorter_max_size++ > 0){ //已经出现多次非B帧的情况，那么我们就能知道P帧间B帧的个数 _sorter_max_size = _frames_since_last_max_pts; //我们记录P帧间时间间隔(也就是多个B帧时间戳增量累计) _dts_pts_offset = (pts - _last_max_pts); //除以2，防止dts大于pts _dts_pts_offset /= 2; } //遇到P帧或关键帧，连续B帧计数清零 _frames_since_last_max_pts = 0; //记录上次非B帧的pts时间戳(同时也是dts)，用于统计连续B帧时间戳增量 _last_max_pts = pts; } //如果pts时间戳小于上一个P帧，那么断定这个是B帧,我们记录B帧连续个数 ++_frames_since_last_max_pts; } //pts放入排序缓存列队，缓存列队最大等于连续B帧个数 _pts_sorter.emplace(pts); if(_sorter_max_size && _pts_sorter.size() > _sorter_max_size){ //如果启用了pts排序(意味着存在B帧)，并且pts排序缓存列队长度大于连续B帧个数， //意味着后续的pts都会比最早的pts大，那么说明可以取出最早的pts了，这个pts将当做该帧的dts基准 auto it = _pts_sorter.begin(); //由于该pts是前面偏移了个_sorter_max_size帧的pts(也就是那帧画面的dts), //那么我们加上时间戳偏移量，基本等于该帧的dts dts = *it + _dts_pts_offset; if(dts > pts){ //dts不能大于pts(基本不可能到达这个逻辑) dts = pts; } //pts排序缓存出列 _pts_sorter.erase(it); return true; } //排序缓存尚未满 return false; } void NtpStamp::setNtpStamp(uint32_t rtp_stamp, uint32_t sample_rate, uint64_t ntp_stamp_ms) { _rtp_stamp_ms = uint64_t(rtp_stamp) * 1000 / sample_rate; _ntp_stamp_ms = ntp_stamp_ms; } uint64_t NtpStamp::getNtpStamp(uint32_t rtp_stamp, uint32_t sample_rate) { uint64_t rtp_stamp_ms = uint64_t(rtp_stamp) * 1000 / sample_rate; if (!_rtp_stamp_ms && !_ntp_stamp_ms) { return rtp_stamp_ms; } if (rtp_stamp_ms > _rtp_stamp_ms) { //时间戳正常增长 _last_ret = _ntp_stamp_ms + (rtp_stamp_ms - _rtp_stamp_ms); return _last_ret; } if (_rtp_stamp_ms - rtp_stamp_ms < 10 * 1000) { //小于10秒的时间戳回退，说明收到rtp乱序了 return _ntp_stamp_ms - (_rtp_stamp_ms - rtp_stamp_ms); } uint64_t max_rtp_ms = uint64_t(UINT32_MAX) * 1000 / sample_rate; if (rtp_stamp_ms < 60 * 1000 && _rtp_stamp_ms > max_rtp_ms - 60 * 1000) { //确定是时间戳溢出 return _ntp_stamp_ms + rtp_stamp_ms + (max_rtp_ms - _rtp_stamp_ms); } //不明原因的时间戳回退，直接返回上次值 return _last_ret; } }//namespace mediakit