[SR-Users] RTPEngine / Transcoding question

[Richard Fuchs]

On 21/05/2019 18.42, Carsten Bock wrote:
> Hi Richard,
>
> Thanks for your reply, understood.
>
> The issue is following (not really an issue, more an optimization):
> At the moment of the offer, I simply don't know, what will be 
> supported by the callee. G711 is however always supported, that's why 
> I don't want to strip it. I send the call to our upstream provider; if 
> he sends it to Telefonica, we get an answer with G722 and G711. If he 
> sends it to Deutsche Telekom, the answer is only G711. However, we 
> don't know, if it's gonna be Telefonica or Deutsche Telekom...
>
> I was thinking about avoiding uneccessary RTP traffic (in HD) between 
> RTPEngine and the device in case of an outbound call. From a 
> signalling perspective, I get the right result, if I use 
> sdp_remove_codecs() in my reply. However, that won't work, since the 
> RTP stream sent from RTPEngine to the device is in HD, regardless of 
> the signalling.

Maybe you want to make your transcoding options also dependent on 
whether G.711 was present in the original offer, and/or in what order 
the codecs were listed? Rtpengine won't do transcoding if both sides 
support the same codec, even if other codec pairings are possible 
(unless `always-transcode` is given). Are you using that option? Are you 
using other options to reorder codecs in the offer? Because normally the 
first supported codec will be used, and rtpengine adds transcoding codec 
offers to the end of the list. So they should only be used if no other 
codec is supported by the callee, unless the callee ignores the listed 
codec preferences, or codecs were reordered, or `always-transcode` was used.

Cheers