[MMUSIC] Wisdom sought: Prioritization of codecs

[Harald Alvestrand <[e-mail]>]

I've been searching RFC 4566 (SDP) for this info, but came up blank....

in an M-line, we typically have

m=video blabla 111 112 113
a=rtpmap:111 ....
a=rtpmap:112 ...
a=rtpmap:113 ....

Section 5.14 says this:

       If the <proto> sub-field is "RTP/AVP" or "RTP/SAVP" the <fmt>
       sub-fields contain RTP payload type numbers.  When a list of
       payload type numbers is given, this implies that all of these
       payload formats MAY be used in the session, but the first of these
       formats SHOULD be used as the default format for the session.

Now, the questions...

1) In offer/answer, does this sequence in an offer mean that the offerer 
prefers that the answerer use codec 111, if supported?

2) in offer/answer, does this sequence in an answer mean that the 
answerer prefers that the offerer use codec 111?

3) is there any preference expressed between codec 112 and codec 113?

4) Should the sequence of a=rtpmap: lines be completely ignored, or does 
it matter?

I'm trying to fix a bug, and want to make sure I fix it according to spec.

                Harald