Subject: Re: In band signalling of PT

From: John Lazzaro <[email-masked]>
Date: Wed, 13 Sep 2000 14:27:19 -0700

[Colin Perkins writes ...]

> Does it help? Since you need out of band information to know where to find
> the media stream, you may as well include information about the format of
> the media.

I think it could really help move the conversation forward if one of
the pro-inband folks explicitly describes the out-of-band system they
have in mind for finding the initial media stream, and explain why this
out-of-band system can't be based on IETF protocols known to be able
to handle the tasks that the pro-inband folks are requesting RTP changes
to handle. There's an implicit sense of "implementing those IETF protocols
on a dumb MPEG-4 terminal is too complex/costly" -- once you make that
implicit statement explicit and supported, there's an opportunity to   
move forward with the discussion ...

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John Lazzaro -- Research Specialist -- CS Division -- EECS -- UC Berkeley
lazzaro [at] cs [dot] berkeley [dot] edu     www.cs.berkeley.edu/~lazzaro
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From: Ross Finlayson <[email-masked]>
Date: Wed, 13 Sep 2000 22:40:26 -0700

Another point to keep in mind here is that - in the general case - a 
multimedia session can consist of *more than one* RTP stream (e.g., one RTP 
stream for video; another for audio; another for subtitles).  Even if each 
individual stream were - somehow - to have in-band information about its 
payload format, etc., you'd still need a way of describing which individual 
RTP streams make up an entire session.

Although the MPEG world has often assumed that multiple media are 
multiplexed together in a single stream, RTP has more flexibility than this.

         Ross.