[Live-devel] RTCP and synchronization

[Julian Lamberty]

Hi!

As RTCP SR packets carry NTP ans RTP timestamps I would like to know how 
they are used to sync to streams. 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? 
For example I have (taken from wireshark):

RTCP Sender Report:

Arrival Time: Jul  2, 2007 14:34:00.669515000
MSW and LSW as NTP timestamp: Jul  2, 2007 12:27:10.3529 UTC
RTP timestamp: 2965177770

But my video stream has timestamps beginning at higher values.

RTP packet:

Arrival Time: Jul  2, 2007 14:34:00.651933000
Timestamp: 3583401060

How do these times correspond to each other?

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)? When I 
send out the manipulated videoframes, they get a new RTP timestamp 
offset and the receiver will not be able to sync them to the 
unmanipulated audio stream...?