Subject: [IPTEL] h323 and Video

From: "Amar, Yigal" <[email-masked]>
Date: Wed, 4 Oct 2000 19:22:28 +0300

Hi ,

I have two question , and I hope this is the right place to ask ..

1)  why is it that video codecs do not require jitter buffering while audio
codecs do ??

2) I'm cupturing a H.261 video stream and writing it to a file , when
transmiting/playing back  the 
    h.261 frames from the file, I need to indicate that the first frame is
an " I frame " , or else the playback is fuzzy.
    How do I do that  ? is it in the h.261 header or RTP header ??

Thanks in advance

Yigal Amar 
972-3-645-4175 
[email-masked] 

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---

From: Paul Long <[email-masked]>
Date: Wed, 4 Oct 2000 20:20:37 -0500

Yigal,

1) JItter buffers are not required by either audio or video, would benefit
both, but benefit audio the most because of the more ephemeral nature of
audio. Receiver-generated jitter estimates are very useful to a video
encoder and media scheduler. B.14.3/H.245v5 describes the semantics for the
JitterIndication messages as typically applied to a video channel, and SR/RR
interarrival jitter described in RFC 1889 is media neutral. Also check out
sections 4.2 and 4.3 in
http://www.kashpureff.org/nic/drafts/draft-ietf-mmusic-confarch-00.txt.html
and especially section 7.3 in
http://www.tik.ee.ethz.ch/~cobrow/deliverables/d3-2/d3-2.html.

2) Whether a frame is INTER or INTRA is indicated in the MTYPE field within
the H.261 data stream (see Table 2 in the H.261 Recommendation). But a frame
is either an INTER or INTRA frame inherently and cannot be converted from
one to the other simply by changing the MTYPE, so I wouldn't try to modify
the stream. If the first frame you recorded is not an INTRA because, for
example, it got lost in transmission, you might want to search the video
stream for the first INTRA and discard all frames up to that point before
re-transmission/playback.

Hope that helps.

Paul Long
Smith Micro Software, Inc.

-----Original Message-----
From: [email-masked]
[mailto:[email-masked]]On Behalf Of Amar, Yigal
Sent: Wednesday, October 04, 2000 11:22 AM
To: [email-masked]
Subject: [IPTEL] h323 and Video

Hi ,

Thanks in advance

Yigal Amar
972-3-645-4175
[email-masked]

---

From: "Dr. Carsten Bormann" <[email-masked]>
Date: Thu, 5 Oct 2000 10:35:33 +0200

One minor comment:

The most recent version of this document is at:

http://search.ietf.org/internet-drafts/draft-ietf-mmusic-confarch-03.txt

Also, you can find a printed version in

%A Mark Handley
%A Jon Crowcroft
%A Carsten Bormann
%A Jörg Ott
%T Very Large Conferences on the Internet: The Internet Multimedia
Conferencing Architecture
%J Computer Networks
%V 31
%N 3
%D February 1999
%P 191-204

Gruesse, Carsten