[Live-devel] Calculating rtptime for RTSP/PLAY-Response "RTP-Info" header

[Chris Burns]

Sorry, I should have been more clear in my question...
 
I'm specifically trying to work out how to create the "RTP-Info" header
in a RTSP/PLAY-Response.
 
It looks quite simple. Grab the RTP-Time & SeqNum of the first RTP
packet sent on each stream to the client, format it correctly and we're
done. Unfortunately, this causes low-powered clients (like cell-phones)
to have terrible A/V sync.
 
If you look at the example I posted below, the first RTP packets going
to the client for each stream (packets 922 & 926) have details like
this:
 
 
922: RTP/3456 to CLIENT
    Seq: 39932
    RTP: 383841717
 
926: RTP/3458 to CLIENT
    Seq: 59095
    RTP: 671369087
 
But the RTSP/PLAY-Response looks like this:
 
925: RTSP/PLAY-Response to CLIENT
    RTP-Info:
url=rtsp://172.28.15.239/rtpencoder/Blah.sdp/streamid=1;seq=39932;rtptim
e=383841717,
 
url=rtsp://172.28.15.239/rtpencoder/Blah.sdp/streamid=0;seq=59095;rtptim
e=671239890
 
 
There is a delta of -129197 in the RTP-Time specified in the "RTP-Info"
header and the RTP-Time in the packet with SeqNum==59095. How is this
delta calculated? Anyone know?
 
Cheers,
 
ChrisB

Chris Burns
M: +64 21 391 286
chris.burns at abdeus.com

	Sent: Thursday, 07 August 2008 22:32
	To: live-devel at ns.live555.com
	Subject: [Live-devel] Calculating rtptime for RTSP/PLAY-Response
"RTP-Info"header
	
	
	
	Hi all,
	 
	I'm trying to figure out how to calculate the RTPTime values in
the RTSP/PLAY-Response "RTP-Info" header, based on an incoming live
RTP/RTCP stream(s) from a live encoder.
	 
	I've pulled apart an HUSM packet dump and the critical section
looks something like this:
	 
	 
	 
	
	769: RTCP-SR/9301 from LENC
	    NTP: MSW: 3403825895 (0xcae242e7); LSW: 133143986
(0x07ef9db2)  ==> Nov 12, 2007 03:11:35.0310 UTC
	    RTP: 670943030
	 
	803: RTCP-SR/9303 from LENC
	    NTP: MSW: 3403825896 (0xcae242e8); LSW: 64424509
(0x03d70a3d) ==> Nov 12, 2007 03:11:36.0150 UTC
	    RTP: 383790848
	 
	840: RTCP-SR/9301 from LENC
	    NTP: MSW: 3403825897 (0xcae242e9); LSW: 64424509
(0x03d70a3d) ==> Nov 12, 2007 03:11:37.0150 UTC
	    RTP: 671123120
	 
	871: RTSP/PLAY-Request from CLIENT
	 
	881: RTCP-SR/9303 from LENC
	    NTP: MSW: 3403825898 (0xcae242ea); LSW: 64424509
(0x03d70a3d) ==> Nov 12, 2007 03:11:38.0150 UTC
	    RTP: 383834926
	 
	882: RTCP-SR/3457 to CLIENT
	    Same as 881
	
	906: RTCP-RR/3457 from CLIENT
	 
	919: RTCP-SR/9301 from LENC
	    NTP: MSW: 3403825899 (0xcae242eb); LSW: 133143986
(0x07ef9db2) ==> Nov 12, 2007 03:11:39.0310 UTC
	    RTP: 671303570
	 
	920: RTCP-SR/9301 to CLIENT
	    Same as 919
	 
	921: RTP/9302 from LENC
	    Seq: 39932
	    RTP: 383841717
	 
	922: RTP/3456 to CLIENT
	    Same as 921
	 
	923: RTP/9300 from LENC
	    Seq: 59095
	    RTP: 671369087
	 
	924: RTP/9302 from LENC
	    Seq: 39933
	    RTP: 383842741
	 
	925: RTSP/PLAY-Response to CLIENT
	    RTP-Info:
url=rtsp://172.28.15.239/rtpencoder/Blah.sdp/streamid=1;seq=39932;rtptim
e=383841717,
	
url=rtsp://172.28.15.239/rtpencoder/Blah.sdp/streamid=0;seq=59095;rtptim
e=671239890
	 
	
	926: RTP/3458 to CLIENT
	    Seq: 59095
	    RTP: 671369087
	
	 
	
	927: RTP/3456 to CLIENT
	    Seq: 39933
	    RTP: 383842741
	 
	 
	 
	How in the world did HUSM come up with "rtptime=671239890"?????
	 
	Is there any reference or commonly cited material about how
these values are calculated?
	 
	Thanks in advance,
	 
	ChrisB
	 

	Chris Burns
	M: +64 21 391 286
	chris.burns at abdeus.com

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