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

[Chris Burns]

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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