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<div class="moz-cite-prefix">-------- Original Message --------<br>
Subject: Re: [Live-devel] Delay problem of the first RTCP "SR"
packet<br>
From: Steve Ha <a class="moz-txt-link-rfc2396E" href="mailto:steveha@u2sr.com"><steveha@u2sr.com></a><br>
To: LIVE555 Streaming Media - development & use
<a class="moz-txt-link-rfc2396E" href="mailto:live-devel@us.live555.com"><live-devel@us.live555.com></a><br>
Date: 2021-01-22 04:52+0300<br>
</div>
<blockquote type="cite"
cite="mid:CAOckaMe=nvxvQaV_W=mf93m+VjBJatVLU+QYGotjM22kg1fhuw@mail.gmail.com">
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<div dir="ltr">Thanks for your quick and useful response,
<div>I have checked it and admit that the "SR" always comes to
the client before the first RTP packet.</div>
<div><br>
</div>
<div>But I still wonder about two things: </div>
<div>1) Since the RTPTimestamp bound to the first "SR" is
different from the one bound to the first RTP packet, how can
PTS be synchronized to the server's NTP correctly at the
client side?</div>
</div>
</blockquote>
<p>Steve,</p>
<p>This might get mangled (ASCII art formatting) but</p>
<p><br>
</p>
<p>From RFC 3550, 6.5.1</p>
<pre class="newpage"> +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
sender | NTP timestamp, most significant word |
info +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NTP timestamp, least significant word |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RTP timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+</pre>
<p>The NTP time stamp in the sender report is accompanied by the
random offset NTP stream timestamp also used RTP packet headers,
so the receiver should be able to carry forward the offset between
sender NTP time and RTP packets.</p>
<p><br>
</p>
<blockquote type="cite"
cite="mid:CAOckaMe=nvxvQaV_W=mf93m+VjBJatVLU+QYGotjM22kg1fhuw@mail.gmail.com">
<div dir="ltr">
<div>2) Does PTS at client always monotonically increase even in
case RTPTimestamp (32-bit) is wrapped around?.</div>
</div>
</blockquote>
<p><br>
</p>
<p>that I don't know....<br>
</p>
<blockquote type="cite"
cite="mid:CAOckaMe=nvxvQaV_W=mf93m+VjBJatVLU+QYGotjM22kg1fhuw@mail.gmail.com">
<div dir="ltr">
<div><br>
</div>
<div>Regards.</div>
<div>Steve.</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Fri, Jan 22, 2021 at 4:01
PM Ross Finlayson <<a href="mailto:finlayson@live555.com"
moz-do-not-send="true">finlayson@live555.com</a>> wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><br>
<br>
> On Jan 22, 2021, at 4:05 PM, Steve Ha <<a
href="mailto:steveha@u2sr.com" target="_blank"
moz-do-not-send="true">steveha@u2sr.com</a>> wrote:<br>
> <br>
> My question is how can I force the first RTCP "SR" packet
to be delivered at the same time as the first RTP packet so
that the RTSP client could get all frames with correct PTS?<br>
<br>
Basically, you can’t. (But even if you could, there’d be no
guarantee that it would be received, as it (like all RTCP (and
RTP packets) are datagrams.)<br>
<br>
However, our RTSP server implementation *does* send an initial
RTCP “SR”, before the first RTP packet, precisely for this
reason. (See “OnDemandServerMediaSubsession.cpp”, line 550.)<br>
<br>
<br>
Ross Finlayson<br>
Live Networks, Inc.<br>
<a href="http://www.live555.com/" rel="noreferrer"
target="_blank" moz-do-not-send="true">http://www.live555.com/</a><br>
<br>
<br>
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</blockquote>
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