Re: [AVT] Interop issue with H263-1998

[Colin Perkins <csp at csperkins.org>]

On 8 Sep 2007, at 04:20, Randell Jesup wrote:
...
> As best I can tell, there were various ad-hoc SDP setups for H.263  
> before
> RFC 4629.  Many of them supported optional parameters (in particular
> resolution and MPI), in contradiction of RFC 4629 section 9.1  
> (which says
> that old implementations will ignore these parameters).  For added  
> fun, RFC
> 4629 doesn't specify the grammar for the fmtp parameters; it assumes
> silently (based on other RFCs one assumes) that they'll be  
> delimited by
> semicolons.  Many/most existing H.263/263+ applications delimit fmtp
> parameters with spaces instead.  RFC 4566 doesn't even mention  
> semicolons
> or the details of the ftmp string -- 4566 considers the fmtp string  
> to be
> none of its business.  The problem is that different implementers  
> may make
> different assumptions about the grammar for the fmtp line.  Perhaps  
> I've
> missed something...

RFC 4629 section 8.2 states:

   o The optional parameters, if any, MUST be included in the "a=fmtp"
     line of SDP.  These parameters are expressed as a media type
     string, in the form of a semicolon-separated list of
     parameter=value pairs.

The legal syntax of a media type string is specified in the MIME  
RFCs, which are included by reference via a citation to RFC 3555.

--
Colin Perkins
http://csperkins.org/



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