Subject: RE: [AVT] New draft-ietf-avt-mpeg4-simple-07

From: Franceschini Guido <[email-masked]>
Date: Wed, 26 Feb 2003 16:40:15 +0100

Colin,

your reply makes me very happy. I'd love to see this draft becoming an RFC.
So apparently it is already specified that AU-Index will never be 0 when "useful". That is just perfect -I was assuming that 0 was an acceptable coded value for the variable duration case-.
I failed however to find such a statement. Could you or Jan point me to it ?

Thanks again
Guido

-----Original Message-----
From: Colin Perkins [mailto:[email-masked]]
Sent: Wednesday, February 26, 2003 4:19 PM
To: Franceschini Guido
Cc: [email-masked]; [email-masked]
Subject: Re: [AVT] New draft-ietf-avt-mpeg4-simple-07

Guido,

--> Franceschini Guido writes:
>Jan,
>
>unfortunately I have to disagree with the text you modified with respect 
>to Colin's text.
>I am fine with supporting early implementations, but the wording used 
>is, IMHO, not suitable. More specifically you wrote:
>
>   If the "constantDuration" parameter is not present, then Access
>   Units are assumed to have a variable duration, unless the AU-Index
>   is present and coded with the value 0 in each RTP packet.
>
>How can a receiver implement the rule above? Should it observe 1, 10, 
>1000 or infinite packets before determining that the "AU-Index is 
>present and coded with the value 0 in each RTP packet" ?

One packet is sufficient.  If the Access Units have variable duration, the
AU-Index will never be zero, if they have fixed duration it will always be
zero. The rest of the paragraph you quoted makes this explicit.

>What is the exact legacy that you want to support ? Maybe there is a 
>different mechanism to support it. For example, a specific mode 
>definition might IMPLY a specific "constantDuration" value, without 
>writing this explicitely in the SDP.

Not if it wishes to comply with this specification.

Colin
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---

From: Colin Perkins <[email-masked]>
Date: Wed, 26 Feb 2003 10:49:51 -0500

Guido,

The paragraph you quoted continues with "When transmitting Access Units
of variable duration ... the transmitter MUST use the AU-Index to encode
the index information required for reordering..." which implies non-zero
values to my reading.

Colin

--> Franceschini Guido writes:
>So apparently it is already specified that AU-Index will never be 0 when
>"useful". That is just perfect -I was assuming that 0 was an acceptable
>coded value for the variable duration case-.  I failed however to find such
>a statement. Could you or Jan point me to it ?
>
>Thanks again
>Guido
>