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Re: [AVT] Generic RTP payload format for time-lined static media

Ross Finlayson <finlayson@live.com> Sat, 14 July 2001 02:04 UTC

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Date: Fri, 13 Jul 2001 19:03:40 -0700
To: avt@ietf.org
From: Ross Finlayson <finlayson@live.com>
Subject: Re: [AVT] Generic RTP payload format for time-lined static media
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At 07:18 AM 7/13/01, Magnus Westerlund wrote:
>I have submitted a new draft with the title: Generic RTP payload format
>for time-lined static media.
...
>Untill the draft is available in the IETF directory you can find it
>here:
>http://standards.ericsson.net/westerlund/draft-westerlund-avt-rtp-static-media-00.txt
>
>Please read the draft and comment on it. I also hope to have the
>possiblity to present and discuss it in London.

Overall, I like this approach a lot.  For a while this working group has 
been considering how to transport time-based 'metadata' over RTP, and the 
general approach you're taking - a common payload format defined, along 
with various application-specific 'profiles' - seems like a good way to do 
this.  Personally, I'm interested in using something like this to transport 
"ID3" tags <http://www.id3.org/>; these are commonly used to describe 
meta-data for music tracks (and also allow for features like 
time-synchronized lyrics).

Some specific comments on your proposal:

- Section 4 - Requirements:
         - Multicast capabilities The payload format specification SHOULD
         allow streaming of time-lined static media objects using 
multicasting.

I'd make this a MUST, not SHOULD.

- Section 5.1 - RTP Header Usage:
         Timestamp: The timestamp is used for identifying the time when
         the object shall be used by the receiver(s). The timestamp MUST
         be identical for all packets being part of the same object, i.e. the
         timestamp is used for binding packets to the correct object.
         If two different objects are going to be used at the same time,
         they MUST have different timestamps.

This last requirement seems unnecessary.  What's wrong with having two or 
more objects with the same start time?  There seems to be no reason to 
disallow this.

- Section 8.1: Confidentiality
         To achieve confidentiality of the transported media, all RTP payload
         bits MUST be encrypted.

This wording implies that the use of encryption is manditory with this 
payload format, which is not what you really meant here, right?

         Ross.



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