[AVT] Signalling comments on draft-hatanaka-avt-atrac-family-00.txt

[Magnus Westerlund <magnus.westerlund at ericsson.com>]

Hi Hatanaka and Matthew,

I have looked at the draft and will divide the comments into separate 
mails as they have different importance's. The simplification looks 
promising. This mails discuss the rather major signalling problem.

There is need to resolve how the setup signalling for this payload 
format will work. The normal model is that one defines a MIME type, 
potentially with parameters that represents the codec over the defined 
payload format. If one has configuration information that needs to be 
conveyed these are included as MIME parameters that then is mapped into 
the description format, like the a=fmtp line in SDP. You will need to do 
the same. However as you have defined one payload format for a family of 
codecs there is importance that the you ensure that it can conveyed 
exactly what codec version, and its necessary parameters. I see two main 
branch of solutions, either use separate MIME types for each codec 
(probably more suitable if the number of codecs are few) or use a 
parameter that declares what codec is to be used. The first alternative 
is also more appropriate if the configuration information is different 
between the codecs.

Please look also at my recent mails regarding channel information. To my 
understanding some of the ATRAC codecs support multi-channel content, 
thus also you will have these considerations.

Please look at RFC 3267 or RFC 3558 for how it can look when defining 
the MIME parameter list. Please note that most of these parameters are 
in regards to the payload format configuration. For a proposal 
containing more codec related parameters, please look at 
draft-ietf-avt-rtp-h264-03.txt

I am sorry that I can't be more specific, however my knowledge of the 
ATRAC codec is very limited. However if you want help you are welcome to 
contact us chairs.

Cheers


Magnus Westerlund 
Multimedia Technologies, Ericsson Research EAB/TVA/A
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