Interpolate sender time in case of missing re ference timestamp meta, sync with sender.

Hi.
 
Given following chunk of code:
 
 var metaTs = buf.GetReferenceTimestampMeta();
  if (metaTs.Timestamp > 0)
  { //ok 
    cameraTs = metaTs.Timestamp;
   }
 else
  {  //what to do here??
       cameraTs = UtcNow;
 }
 
For now I use machine time which is not great —  few seconds shift can be.
The obvious  but coarse and not robust solution is to use cameraTs += 1/fps, but
it will give millisecond precision. Can we do better? Can I use pipeline clocks to interpolate
missing camera timestamps? Maybe it can be done automatically by gst within some settings, like
Rtspsrc-buffer-mode or   Rtspsrc-ntp-time-source ?
 
My current rtsp settings are:
 rtspSrc["add-reference-timestamp-meta"] = true;
 rtspSrc["buffer_mode"] = 0; //Only use RTP timestamps
 
Thanks in advance.
 
 
 
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С Уважением,
Шаров Антон