You should never need to concern yourself with “RTP timestamps”.  Instead, you 
should consider only “presentation times”.  (Our software automatically 
converts presentation times to RTP timestamps (when sending), and RTP 
timestamps to presentation times (when receiving).  Our proxy server (and other 
application code that acts as RTSP clients and/or RTSP servers) works only with 
presentation times.  So, from now on, “presentation times” are the only things 
you should concern yourself with.

When streaming video codecs, frames (or, more precisely, “NAL units” for H.264 
and its successors) are transmitted in "decoding order" (the order in which the 
received frames will be fed to the decoder), not “display order” (the order in 
which the received frames will be displayed on a screen).  Sometimes, video 
frame N can’t be decoded without information from video frame N+1; in such a 
case, therefore, frame N+1 will be transmitted before frame N.

Presentation times correspond to display order, not decoding order - which is 
why you sometimes see them decrease.


Ross Finlayson
Live Networks, Inc.
http://www.live555.com/


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