Re: [AVT] Representing Boolean MIME-type parameters in SDP?

[Magnus Westerlund <magnus.westerlund at ericsson.com>]

Hi Ross,

It is required for RTP media types to have values. This is due to the 
following in RFC 3555:

"3. Mapping to SDP Parameters

   The representation of a MIME media type is specified in the syntax of
   the Content-Type header field in RFC 2045 [6] as follows:

      type "/" subtype  *(";" parameter)

   Parameters may be required for a particular type or subtype or they
   may be optional.  For media types which represent RTP payload
   formats, the parameters "rate", "channels", "ptime", and "maxptime"
   have general definitions (given above) that may apply across types
   and subtypes.  The format for a parameter is specified in RFC 2045 as

      attribute "=" value

   where attribute is the parameter name and the permissible values are
   specified for each parameter.  The value may need to be a quoted
   string if it contains any of the special characters listed in RFC
   2045."


So the usage you have witnessed is ilegal.

Cheers

Magnus


Ross Finlayson wrote:
> I recently encountered a MPEG-4 video + AMR audio RTSP/RTP session whose 
> SDP lines contained the following (for the AMR audio stream):
>
> 	a=rtpmap:97 AMR/8000
> ...
> 	a=fmtp:97 octet-align
>
> Is that last line legal?  I had thought that only the following would be legal:
> 	a=fmtp:97 octet-align=1
>
> RFC 3267 (which defines the RTP payload format for AMR) defines the 
> "octet-align" MIME parameter as follows:
> 	"octet-align: Permissible values are 0 and 1."
>
> So, for Boolean MIME parameters like this, is it permissible to omit the 
> value assignment in the SDP "a=fmtp:" line, thereby assuming the value 
> 1?  I had assumed not (and in fact our own RTSP client code got confused by 
> the example above), but it would be nice to get some clarification of this 
> question, in case examples like the one above become commonplace.
>
> 	Ross Finlayson
> 	LIVE.COM
> 	<http://www.live.com/>
>
>
> _______________________________________________
> Audio/Video Transport Working Group
> avt at ietf.org
> https://www1.ietf.org/mailman/listinfo/avt


--

Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
----------------------------------------------------------------------
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Torshamsgatan 23           | Fax   +46 8 7575550
S-164 80 Stockholm, Sweden | mailto: magnus.westerlund at ericsson.com

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