[Freeswitch-users] SDP with 2 m=audio lines

[Sergey Okhapkin]

Which ptime will be selected for codec 0? It is in both m=audio lines.

m=audio 24598 RTP/AVP 0 101 13
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
a=ptime:30
m=audio 24598 RTP/AVP 98 0 8 3 101 13
a=rtpmap:98 SILK/8000
a=fmtp:98 useinbandfec=1; usedtx=0
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
a=ptime:20


On Tuesday 14 February 2012 13:10:56 Anthony Minessale wrote:
> In your case FS to FS, your FS will parse both m= lines in order they
> are put in the sdp and choose the first stream it prefers based on
> your codec prefs.  Its functionally identical to putting them all in
> one m= line only they are grouped by ptime.
> 
> 
> 
> 
> 
> On Tue, Feb 14, 2012 at 12:40 PM, Sergey Okhapkin
> 
> <sos at sokhapkin.dyndns.org> wrote:
> > But RFC 3388 says (in 1. Introduction):
> > 
> >   An SDP session description typically contains one or more media lines
> >   - they are commonly known as "m" lines.  When a session description
> >   contains more than one "m" line, SDP does not provide any means to
> >   express a particular relationship between two or more of them.  When
> >   an application receives an SDP session description with more than one
> >   "m" line, it is up to the application what to do with them.  SDP does
> >   not carry any information about grouping media streams.
> > 
> > On Tuesday 14 February 2012 11:40:40 Anthony Minessale wrote:
> >> The word undefined does not even appear in that RFC.
> >> 
> >> RFC 2327 (the one that actually describes SDP) is the relevant one:
> >> 
> >> " A session description may contain a number of media descriptions.
> >>    Each media description starts with an "m=" field, and is terminated
> >>    by either the next "m=" field or by the end of the session
> >>    description.  A media field also has several sub-fields: "
> >> 
> >> 
> >> The ptime attribute cannot be applied to a single codec mentioned in a
> >> m= line it must apply to all of them.
> >> Once you have 2 different ptimes in the same description you have no
> >> choice but to split it into different m= lines for each sep ptime.
> >> 
> >> If you dislike this behavior then set:
> >> 
> >> sdp_m_per_ptime=false
> >> 
> >> either globally in vars.xml or in your dialplan on a per leg basis.
> >> 
> >> 
> >> 
> >> 
> >> 
> >> 
> >> 
> >> On Tue, Feb 14, 2012 at 7:39 AM, Sergey Okhapkin
> >> 
> >> <sos at sokhapkin.dyndns.org> wrote:
> >> > I noticed that recent freeswitch versions could send SDP with 2
> >> > m=audio lines. Per RFC 3388, the behavior is undefined this case.
> >> > I don't know how to reproduce the problem, I see such packets
> >> > coming from my customers. Here is an example:
> >> > 
> >> > INVITE sip:xxxxxxxxxxxx at sip.callwithus.com SIP/2.0
> >> > ...
> >> > User-Agent: FreeSWITCH-mod_sofia/1.0.head-git-eeeaf41 2012-02-10
> >> > 17-27-50 -0600 ....
> >> > 
> >> > v=0
> >> > o=FreeSWITCH 1329167961 1329167962 IN IP4 xx.xx.xx.xx
> >> > s=FreeSWITCH
> >> > c=IN IP4 xx.xx.xx.xx
> >> > t=0 0
> >> > m=audio 24598 RTP/AVP 0 101 13
> >> > a=rtpmap:101 telephone-event/8000
> >> > a=fmtp:101 0-16
> >> > a=ptime:30
> >> > m=audio 24598 RTP/AVP 98 0 8 3 101 13
> >> > a=rtpmap:98 SILK/8000
> >> > a=fmtp:98 useinbandfec=1; usedtx=0
> >> > a=rtpmap:101 telephone-event/8000
> >> > a=fmtp:101 0-16
> >> > a=ptime:20
> >> > 
> >> > 
> >> > Hmm, I just realized that this SDP is buggy - 2 audio streams on
> >> > the
> >> > same
> >> > port, with common codecs, but with different ptime :-)
> >> > 
> >> > __________________________________________________________________
> >> > ______ _
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> >> > 
> >> > 
> >> > 
> >> > 
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> > _
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> > 
> > 
> > 
> > 
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