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

From: [email-masked]
Date: Wed, 26 Feb 2003 03:02:45 +0100

Dear all,

This is to let you know that I just submitted 
draft-ietf-avt-mpeg4-simple-07 for upload to the IETF. For your 
convenience I attached the draft to this email.

Compared to -06 there are several editorial improvements. In addition, all 
comments provided by Colin are incorporated with one small difference. 
Colin suggested the following text on interleaving in 3.2.3.2 (page 17):

    If the "constantDuration" parameter is not present, then Access Units
    are assumed to have a variable duration. In this case, the transmitter
    MUST use the AU-Index to encode the index information required for
    re-ordering, and the receiver MUST use that value to determine the
    index of the first AU in the RTP packet. ...

I changed this to the following text, in order to accomodate "early 
implementations" that do not use the constantDuration parameter when 
transmitting constant duration AUs. 

   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. When 
   transmitting Access Units of variable duration, then the 
   "constantDuration" parameter MUST NOT be present, and the 
   transmitter MUST use the AU-Index to encode the index information 
   required for re-ordering, and the receiver MUST use that value to 
   determine the index of each AU in the RTP packet. ...

From my perspective the document is ready now. All known comments are 
incorporated (Colin and Steve thanks for your help !) and therefore I 
think we are done, unless any further issues are identified. 

Best regards / Groeten,

Jan

-----------------------------------------------------------
Jan van der Meer
Philips - MP4Net
Prof Holstlaan 4
Building WDB-1
P.O. Box 80021
5600 JZ Eindhoven
The Netherlands
Phone +31 402 735 774
Fax +31 402 735 545

---

From: [email-masked]
Date: Wed, 26 Feb 2003 23:28:41 +0100

Guido,

I agree with Colin to a large extend. We are talking about the case of 
interleaving where we have a certain interleaving pattern. In case of 
variable duration, any AU-index value (including zero) only occurs again 
after the applied interleaving pattern "passed sufficiently". If there are 
two subsequent RTP packets with the same AU-index value, then this is 
clearly one of the roll-over problems that the referenced rule states 
"MUST NOT" occur. 

But note that the value zero (as any other value) may occur once in a 
while, but that the AU-index value always differs in subsequent RTP 
packets in case of variable duration. Which means that the answer to your 
original question is that you don't need to look further than two 
subsequent RTP packets. 

Best regards,

Jan

Colin Perkins <[email-masked]>
2003-02-26 04:49 PM

        To:     Franceschini Guido <[email-masked]>
        cc:     Jan vanderMeer/EHV/CE/PHILIPS@EMEA3
[email-masked]
        Subject:        Re: [AVT] New draft-ietf-avt-mpeg4-simple-07
        Classification: 

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:
>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:
>>
>>   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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