Re: [rtcweb] I-D Action: draft-alvestrand-one-rtp-00.txt

[Harald Alvestrand <[e-mail]>]

On 08/15/11 16:52, Randell Jesup wrote:
> On 8/15/2011 4:20 AM, Harald Alvestrand wrote:
>
>> On 08/12/11 17:24, Paul Kyzivat wrote:
>>> That brings up another peculiar case. Suppose the m-lines in question
>>> were, in order, video, audio, and timed text, and the answerer again
>>> only wanted to use audio and timed text. In that case, will it still
>>> want to use the port offered for video??? How would the answer be
>>> constructed, and where would the answering port be placed?
>> That is a strong argument in favour of "just don't give any codecs". I'm
>> adding that too.
>
> If you're suggesting "m=video 4321 RTP/AVP" as an SDP line, it's 
> illegal to
> not have a payload listed, I'm afraid (though many implementations 
> will accept
> it).  That includes when you reject an m= line with port 0.
Hm. Yes, since a=rtpmap attributes are only required for dynamic 
numbers, leaving all the a=rtpmap: attributes out doesn't help, and the 
grammar of the m= line is given in RFC 4566 as

       m=<media> <port> <proto> <fmt> ...

  which seems like "one or more". So scratch that idea.
>
>>> It occurs to me that there is another "special" port that might be
>>> co-opted for use here: port 9, the discard port.
>> Magic numbers are bad for technological health. I don't think I'd like
>> to see that.
>
> Agreed, though occasionally it's ok, even if not optimal (port 0 for 
> reject for example).
>
>
Yup, zero and one are kind of OK to have magical.