添加dts生成算法，兼容含B帧的rtsp推流

src/Common/Stamp.cpp

@@ -42,13 +42,14 @@ int64_t DeltaStamp::deltaStamp(int64_t stamp) {
     }
 
     int64_t ret = stamp - _last_stamp;
-    if(ABS(ret) < MAX_DELTA_STAMP){
-        //时间戳变化不明显
+    if(ret >= 0){
+        //时间戳增量为正，返回之
         _last_stamp = stamp;
-        return ret;
+        //在直播情况下，时间戳增量不得大于MAX_DELTA_STAMP
+        return  ret < MAX_DELTA_STAMP ? ret : (_playback ? ret : 0);
     }
 
-    //时间戳变化太明显，可能回环了或者seek了
+    //时间戳增量为负，说明时间戳回环了或回退了
     _last_stamp = stamp;
     return _playback ? ret : 0;
 }
@@ -99,4 +100,52 @@ int64_t Stamp::getRelativeStamp() const {
 }
 
 
+bool DtsGenerator::getDts(uint32_t pts, uint32_t &dts){
+    bool ret = false;
+    if(pts == _last_pts){
+        //pts未变，返回上次结果
+        if(_last_dts){
+            dts = _last_dts;
+            ret = true;
+        }
+        return ret;
+    }
+
+    ret = getDts_l(pts,dts);
+    if(ret){
+        //保存本次结果
+        _last_dts = dts;
+    }
+    //记录上次pts
+    _last_pts = pts;
+    return ret;
+}
+
+bool DtsGenerator::getDts_l(uint32_t pts, uint32_t &dts){
+    if(pts > _last_max_pts){
+        if(!_sorter_max_size && _frames_since_last_max_pts && _count_sorter_max_size++ > 0){
+            _sorter_max_size = _frames_since_last_max_pts;
+            _dts_pts_offset = (pts - _last_max_pts) / 2;
+            InfoL << _sorter_max_size << " " << _dts_pts_offset;
+        }
+        _frames_since_last_max_pts = 0;
+        _last_max_pts = pts;
+    }
+
+    _pts_sorter.emplace(pts);
+    ++_frames_since_last_max_pts;
+
+    if(_sorter_max_size && _pts_sorter.size() >  _sorter_max_size){
+        auto it = _pts_sorter.begin();
+        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_sorter.erase(it);
+        return true;
+    }
+    return false;
+}
+
 }//namespace mediakit