[sr-dev] [kamailio/kamailio] Kamailio 5.1.8, error in sdpops, sdp_keep_codecs function (#1983)

Henning Westerholt notifications at github.com
Fri Feb 28 18:56:32 CET 2020

I looked into the SDPops module and also the SDP core parser. Furthermore I read the relevant RFCs more closely.

It seems that this particular situation (having two ftmp for one media/codec) is not valid.

> RFC 4566:
> 6.  SDP Attributes
> [...]
> a=fmtp:<format> <format specific parameters>
>          This attribute allows parameters that are specific to a
>          particular format to be conveyed in a way that SDP does not
>          have to understand them.  The format must be one of the formats
>          specified for the media.  Format-specific parameters may be any
>          set of parameters required to be conveyed by SDP and given
>          unchanged to the media tool that will use this format.  At most
>          one instance of this attribute is allowed for each format.

> RFC 5939:
> 3.13.1.  The "rtpmap" and "fmtp" Attributes
> [...]
>  An "fmtp" attribute capability in a
>    potential configuration for a media format that already has an "fmtp"
>    attribute in the actual configuration may lead to multiple fmtp
>    format parameters for that media format and that is not allowed by
>    SDP [RFC4566].  The delete-attributes MUST be used to ensure that
>    there are not multiple "fmtp" attributes for a given media format in
>    a media description.

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