Subject: [MMUSIC] question on draft-ietf-mmusic-sdp-new-12 ...

From: John Lazzaro <[email-masked]>
Date: Mon, 24 Mar 2003 18:09:13 -0800

Hi everyone,

        Quick 'wording' question on draft-ietf-mmusic-sdp-new-12,
now that maxptime exists as an SDP attribute, is there an
implied "typical" in the ptime attribute definition, i.e.

  This gives the typical length in milliseconds ...

        If maxptime and ptime are intended to be used together
in a session description, this "typical" would seem to be 
implied. However, if maxptime and ptime are intended to be
mutually exclusive (one or the other but not both are permitted
in a session description), the "typical" is probably not 
implied.   

        Thanks in advance ...

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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: Magnus Westerlund <[email-masked]>
Date: Wed, 26 Mar 2003 13:15:18 +0100

Hi John,

The usage of ptime and maxptime is not mutually exclusive neither are 
they required or even recommended to be used together. The usage is 
dependent on application and can be seen as two attributes for 
controlling how the packetization/encoding work. For ptime the "typical" 
you imply does exist in my opinion. It seems reinforced by the following 
sentence from the ptime definition: "It should not be necessary to know 
ptime to decode RTP or vat audio, and it is intended as a recommendation 
for the encoding/packetisation of audio."

when looking at the version 12 draft I think the definition of maxptime 
needs to be addressed. The following sentence:
"The time SHOULD be a multiple of the frame size." This text comes 
directly from AMR definition that has a frame structure but in the SDP 
specification this should be reformulated to cover the more general and 
take sample based codecs into consideration. My proposal for text is:
"The time SHOULD be a multiple of any frame size."

Best Regards

Magnus

-- 

Magnus Westerlund 

Multimedia Technologies, Ericsson Research ERA/TVA/A
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