title: RTP lipsync synchronization
body: <p>Hi could someone please explain to me how to achieve a lipsync between two RTP streams (from the same RTSP session). I'm trying to  calculate proper pts for ffmpeg AVPacket but I'm missing something and I can't get my head around this. 
  I have the following data available to me:<br>
  <strong>u64RTCP_NTP_TS</strong> - NTP timestamp from RTCP Sender Report<br>
  <strong>u32RTCP_TS</strong>  -  Timestamp from the RTCP Sender Report<br>
  <strong>u32AudioRTP_TS</strong> - Timestamp from the Audio RTP packet<br>
  <strong>u32VideoRTP_TS</strong> - Timestamp from the Video RTP Packet</p>
  
  <p>I've searched for an answer but still I can't get a clear picture of how this should be achieved calculation-wise, what am I still missing.</p>