[Live-devel] RTCP and synchronization

[Ross Finlayson]

>As RTCP SR packets carry NTP ans RTP timestamps I would like to know how
>they are used to sync to streams.

As described in RFC 3550.


>  I found out that the RTP timestamp in
>the RTCP SR corresponds to the timevalue which the NTP timestamp indicates.
>
>But why can't I find the RTP timestamp in the packets of my videostream?

Because they're not useful to you.

I'll say this yet again (and hopefully for the last time): Our 
RTP/RTCP implementation automatically computes synchronized 
presentation times using RTP timestamps and RTCP reports.  Code that 
receives a RTP stream (using our library) should never have to look 
at RTP timestamps.  Instead, just use the presentation time.  If you 
are also using RTCP (which you should be), then the presentaton time 
*will* be properly synchronized.


>What leads me to this problem is the question, how I can keep a video
>stream synchronised to an audio stream when I manipulate the video
>stream on its way to the final recipient (i.e. transcoding it)?

Just make sure that frames of the transcoded stream get correct 
presentation times (and that you create a new "RTCPInstance" object 
for the new outgoing stream).
-- 

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