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

[Colin Perkins <csp@isi.edu>]

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:csp@isi.edu]
>Sent: Wednesday, February 26, 2003 4:19 PM
>To: Franceschini Guido
>Cc: jan.vandermeer@philips.com; avt@ietf.org
>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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