Subject: [AVT] RTP TimeStamp-A query

From: shobana meenakshi <[email-masked]>
Date: Thu, 3 Nov 2005 06:23:40 -0800 (PST)

Hi 
 
I would like to ask a doubt from the RFC 2326(RTSP).
It says that for aggregate control the particular stream may not actually generate a packet for the Range time value returned or implied. Thus, there is no guarantee that the packet with the sequence number indicated by seq actually has the timestamp indicated by rtptime.
Why would it be so
?If the server is able to determine the RTP timestamp that would be in synch in the RTSP play response why not use the send the packet with the same RTP time stamp?
If anyone could explain it would be of great help..
 
Thanks and Regards
Shobana V

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From: Magnus Westerlund <[email-masked]>
Date: Thu, 03 Nov 2005 16:11:52 +0100

Hi,

This almost belong more on the MMUSIC list. However your particular 
question is sufficiently related to AVT to be answered here.

> ?If the server is able to determine the RTP timestamp that would be in synch in the RTSP play response why not use the send the packet with the same RTP time stamp?

The reasons that there may not be packet for the same time instant in 
both video and audio. The range + RTP-Info header provides a 
synchronization point. To avoid needing to specify two range <-> TS 
pairs as RTCP does. RTSP compresses this to provide the corresponding TS 
values for one specific point in the range. That allows the receiving 
client to calculate the range value for any received RTP TS.

You should also check sections 14.38 and Appendix B in the updated RTSP 
spec that should provide more explanation on this:
http://www.ietf.org/internet-drafts/draft-ietf-mmusic-rfc2326bis-11.txt

cheers

Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
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