mirror of
https://github.com/ZLMediaKit/ZLMediaKit.git
synced 2024-11-25 20:27:34 +08:00
291 lines
9.6 KiB
C++
291 lines
9.6 KiB
C++
/*
|
||
* 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"
|
||
|
||
//时间戳最大允许跳变30秒，主要是防止网络抖动导致的跳变
|
||
#define MAX_DELTA_STAMP (30 * 1000)
|
||
#define STAMP_LOOP_DELTA (60 * 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, uint64_t ntp_stamp_ms) {
|
||
update(rtp_stamp, ntp_stamp_ms);
|
||
}
|
||
|
||
void NtpStamp::update(uint32_t rtp_stamp, uint64_t ntp_stamp_ms) {
|
||
if (ntp_stamp_ms == 0) {
|
||
//实测发现有些rtsp服务器发送的rtp时间戳和ntp时间戳一直为0
|
||
return;
|
||
}
|
||
_last_rtp_stamp = rtp_stamp;
|
||
_last_ntp_stamp_ms = ntp_stamp_ms;
|
||
}
|
||
|
||
uint64_t NtpStamp::getNtpStamp(uint32_t rtp_stamp, uint32_t sample_rate) {
|
||
if (rtp_stamp == _last_rtp_stamp) {
|
||
return _last_ntp_stamp_ms;
|
||
}
|
||
return getNtpStamp_l(rtp_stamp, sample_rate);
|
||
}
|
||
|
||
uint64_t NtpStamp::getNtpStamp_l(uint32_t rtp_stamp, uint32_t sample_rate) {
|
||
if (!_last_ntp_stamp_ms) {
|
||
//尚未收到sender report rtcp包，那么赋值为本地系统时间戳吧
|
||
update(rtp_stamp, getCurrentMillisecond(true));
|
||
}
|
||
|
||
//rtp时间戳正增长
|
||
if (rtp_stamp >= _last_rtp_stamp) {
|
||
auto diff = static_cast<int>((rtp_stamp - _last_rtp_stamp) / (sample_rate / 1000.0f));
|
||
if (diff < MAX_DELTA_STAMP) {
|
||
//时间戳正常增长
|
||
update(rtp_stamp, _last_ntp_stamp_ms + diff);
|
||
return _last_ntp_stamp_ms;
|
||
}
|
||
|
||
//时间戳大幅跳跃
|
||
uint64_t loop_delta = STAMP_LOOP_DELTA * sample_rate / 1000;
|
||
if (_last_rtp_stamp < loop_delta && rtp_stamp > UINT32_MAX - loop_delta) {
|
||
//应该是rtp时间戳溢出+乱序
|
||
uint64_t max_rtp_ms = uint64_t(UINT32_MAX) * 1000 / sample_rate;
|
||
return _last_ntp_stamp_ms + diff - max_rtp_ms;
|
||
}
|
||
//不明原因的时间戳大幅跳跃，直接返回上次值
|
||
WarnL << "rtp stamp abnormal increased:" << _last_rtp_stamp << " -> " << rtp_stamp;
|
||
update(rtp_stamp, _last_ntp_stamp_ms);
|
||
return _last_ntp_stamp_ms;
|
||
}
|
||
|
||
//rtp时间戳负增长
|
||
auto diff = static_cast<int>((_last_rtp_stamp - rtp_stamp) / (sample_rate / 1000.0f));
|
||
if (diff < MAX_DELTA_STAMP) {
|
||
//正常范围的时间戳回退，说明收到rtp乱序了
|
||
return _last_ntp_stamp_ms - diff;
|
||
}
|
||
|
||
//时间戳大幅度回退
|
||
uint64_t loop_delta = STAMP_LOOP_DELTA * sample_rate / 1000;
|
||
if (rtp_stamp < loop_delta && _last_rtp_stamp > UINT32_MAX - loop_delta) {
|
||
//确定是时间戳溢出
|
||
uint64_t max_rtp_ms = uint64_t(UINT32_MAX) * 1000 / sample_rate;
|
||
update(rtp_stamp, _last_ntp_stamp_ms + (max_rtp_ms - diff));
|
||
return _last_ntp_stamp_ms;
|
||
}
|
||
//不明原因的时间戳回退，直接返回上次值
|
||
WarnL << "rtp stamp abnormal reduced:" << _last_rtp_stamp << " -> " << rtp_stamp;
|
||
update(rtp_stamp, _last_ntp_stamp_ms);
|
||
return _last_ntp_stamp_ms;
|
||
}
|
||
|
||
}//namespace mediakit
|