Re: [AVT] RFC 3984 offer/answer Question

[Randell Jesup <rjesup at wgate.com>]

"Even, Roni" <roni.even at polycom.co.il> writes:
>>      m=video 49170 RTP/AVP 98
>>      a=rtpmap:97 H264/90000
>>      a=fmtp:97 profile-level-id=42A00A; packetization-mode=0;
>
>You just have a problem with the payload type 98 

>>      m=video 49170 RTP/AVP 98
>>      a=rtpmap:98 H264/90000
>>      a=fmtp:98 profile-level-id=42A00A; packetization-mode=0;

Roni -

I think that's invalid for offer/answer, per 8.2.2.  If the offerer wants
to support only level 1.0 (in this case, 42a00a), it *has* to offer it
as a separate payload type in the offer.  The answer cannot add it as
the same payload type, and you're not supposed to add media formats
(payloads) in an answer.


8.2.2.  Usage with the SDP Offer/Answer Model

   When H.264 is offered over RTP using SDP in an Offer/Answer model [7]
   for negotiation for unicast usage, the following limitations and
   rules apply:

   o  The parameters identifying a media format configuration for H.264
      are "profile-level-id", "packetization-mode", and, if required by
      "packetization-mode", "sprop-deint-buf-req".  These three
      parameters MUST be used symmetrically; i.e., the answerer MUST
      either maintain all configuration parameters or remove the media
      format (payload type) completely, if one or more of the parameter
      values are not supported.

         Informative note: The requirement for symmetric use applies
         only for the above three parameters and not for the other
         stream properties and capability parameters.

>
> 
>
> 
>
>> -----Original Message-----
>
>> From: Yuval Nissan [mailto:Yuval.Nissan at audiocodes.com]
>
>> Sent: Wednesday, August 15, 2007 9:19 AM
>
>> To: Randell Jesup; ctrobianni at ecotronics.com
>
>> Cc: Even, Roni; avt at ietf.org
>
>> Subject: RE: [AVT] RFC 3984 offer/answer Question
>
>> 
>
>> I now understand that the following scenario is legal:
>
>> 
>
>> Offerer support up to level 3.
>
>> Offerer -> Answerer SDP message:
>
>> 
>
>>       m=video 49170 RTP/AVP 98
>
>>       a=rtpmap:98 H264/90000
>
>>       a=fmtp:98 profile-level-id=42A01E; packetization-mode=0;
>
>> 
>
>> Answerer support level 1 only.
>
>> Answerer -> Offerer SDP message:
>
>> 
>
>>      m=video 49170 RTP/AVP 98
>
>>      a=rtpmap:97 H264/90000
>
>>      a=fmtp:97 profile-level-id=42A00A; packetization-mode=0;
>
>> 
>
>> The offerer understands that the session should be in level 1.
>
>> 
>
>> Thanks for your feedback,
>
>> Yuval
>
>> 
>
>> 
>
>> -----Original Message-----
>
>> From: Randell Jesup [mailto:rjesup at wgate.com]
>
>> Sent: Tuesday, August 14, 2007 19:25
>
>> To: ctrobianni at ecotronics.com
>
>> Cc: Yuval Nissan; roni.even at polycom.co.il; avt at ietf.org
>
>> Subject: Re: [AVT] RFC 3984 offer/answer Question
>
>> 
>
>> "Cesar Trobianni" <ctrobianni at ecotronics.com> writes:
>
>> >>The level is the highest level supported so level 3 means that you
>
>> also
>
>> >>support level 1. This is specified in RFC 3984.
>
>> >>
>
>> >>B can offer level 3.
>
>> >
>
>> >But still a separate profile-level-id ftmp line per level should be
>
>> >acceptable (as worst-case scenario), right?
>
>> 
>
>> You can only have one fmtp line per payload value.
>
>> 
>
>> You can define multiple payloads with different fmtp's for a media
>
>> stream,
>
>> however.  Responses (payloads and their fmtp's) are matched up against
>
>> the
>
>> offer using a combination of profile-level-id, packetization-mode, and
>
>> (if
>
>> used) the sprop interleave (if I remember correctly - that last one
>only
>
>> applies to packetization-mode 2).
>
>> 
>
>> Assuming anyone implements all of that totally correctly... :-/
>
>> 
>
>> --
>
>> Randell Jesup, Worldgate (developers of the Ojo videophone), ex-Amiga
>OS
>
>> team
>
>> rjesup at wgate.com
>
>> "The fetters imposed on liberty at home have ever been forged out of
>the
>
>> weapons
>
>> provided for defence against real, pretended, or imaginary dangers
>from
>
>> abroad."
>
>>           - James Madison, 4th US president (1751-1836)
>
>> 
>
>> 
>
>> _______________________________________________
>
>> Audio/Video Transport Working Group
>
>> avt at ietf.org
>
>> https://www1.ietf.org/mailman/listinfo/avt


-- 
Randell Jesup, Worldgate (developers of the Ojo videophone), ex-Amiga OS team
rjesup at wgate.com
"The fetters imposed on liberty at home have ever been forged out of the weapons
provided for defence against real, pretended, or imaginary dangers from abroad."
		- James Madison, 4th US president (1751-1836)


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