Re: Replacing an attribute in the SDP

Hi Henning and Daniel,

Thank you very much for the replies. We moved the following configuration
to reply_route{}, and now it inserts "a=sendonly" immediately before the
"a=sendrecv" rather than appending it to the SDP as before. This
configuration does use RTPengine as the call is from a WebRTC client. Have
you any further idea why it's not actually replacing the "a=sendonly"?

                                replace_body_all( "a=sendrecv",
"a=sendonly" );
                                msg_apply_changes();

Daniel, from reading the sdpops documentation it's not clear how to iterate
through an SDP. Could you please give us a pointer on that?

Thanks again.


On Thu, 18 Dec 2025 at 00:23, Daniel-Constantin Mierla <[email protected]>
wrote:

> Hello,
>
>
> On 17.12.25 02:08, David Cunningham via sr-users wrote:
>
> Hello,
>
> We need to replace a=sendrecv with a=sendonly in the 200 OK reply to an
> INVITE. In theory it should be something straightforward, like in the
> onreply_route using:
>
> replace_body_all( "a=sendrecv", "a=sendonly" );
>
> or:
>
> subst_body( '/^a=sendrecv/a=sendonly/' )
>
> Our first problem is that these both are appending a=sendonly to the end
> of the SDP, not replacing values within it. Does anyone know why this might
> happen?
>
> it could be because of conflicting operations with rtpengine (or
> rtpproxy). You could try the replacement in the core reply_route() and then
> use msg_apply_changes.
>
>
>
> Our second problem is that we really only want to do this for video media,
> and not touch the audio media. Are there any text tools that allow you to
> work with specific media within the SDP?
>
> The sdpops has an sdp iterator that could help: once you match the video
> stream, look for the sendrecv attrbute and replace the line.
>
> Cheers,
> Daniel
>
> --
> Daniel-Constantin Mierla (@ asipto.com)twitter.com/miconda -- linkedin.com/in/miconda
> Kamailio Consultancy, Training and Development Services -- asipto.com
> Kamailio World Conference, May 7-8, 2026 - Berlin, Germany -- kamailioworld.com
>
>

-- 
David Cunningham, Voisonics Limited
http://voisonics.com/
USA: +1 213 221 1092
New Zealand: +64 (0)28 2558 3782

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