[Users] add/rewrite a tag/parameter in SDP

[Lenir]

Hey guys,

 

What is the best way to modify the SDP message to always include (if not
replace) the a= tags in a SDP message?

My problem is specifically with g729, according to the RFC, if the
parameter: "a=fmtp:18 annexb=yes" is present or missing then it is assumed
that g729b (g729 with VAD) and if  "a=fmtp:18 annexb=no" is present then the
devices will use g729a (g729 with VAD Disabled). My problem is that some
cisco gateways and ATAs behave differently (of course Cisco always doing it
their way), if "a=fmtp:18 annexb=no" is missing then it assumes that g729a
will be used, instead of following the RFC where it should negotiate g729b.
Also, asterisk doesn't support g729b so I want to avoid using g729b
everywhere in my network.

 

So what is the best way or is there a way, to either:
a) insert "a=fmtp:18 annexb=no" if is not present

b) replace "a=fmtp:18 annexb=yes" for "a=fmtp:18 annexb=no" if it is present

 

 

Thanks in advance!!

 

 

 

Lenir

 

 

p.s. Please see the below excerpt from RFC 3555 regarding how to specify
G729. 

 

RFC 3555 MIME Type Registration of RTP Payload Formats July 2003 

4.1.9. Registration of MIME media type audio/G729 

MIME media type name: audio 

MIME subtype name: G729 

Required parameters: None 

Optional parameters: 

ptime, maxptime 

annexb: indicates that Annex B, voice activity detection, is used or
preferred. Permissible values are "yes" and "no" (without the quotes); "yes"
is implied if this parameter is omitted

 

 

 

 

 

 

 

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