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

[Roland]

> Is there any reference or commonly cited material about how these values
are calculated?

 

"The RTP timestamp represents the sampling instant of the first octet of
data in the frame. It starts from a random initial value and increments at a
media-dependent rate."

 

>From "RTP, Audio and Video for the Internet", Colin Perkins, 2003, ISBN:
0-672-32249-8

 

 

 

From: live-devel-bounces at ns.live555.com
[mailto:live-devel-bounces at ns.live555.com] On Behalf Of Chris Burns
Sent: Thursday, August 07, 2008 3:32 AM
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;rtptime=38
3841717,

 
url=rtsp://172.28.15.239/rtpencoder/Blah.sdp/streamid=0;seq=59095;rtptime=67
1239890

 

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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