[SR-Users] RTPEngine / Transcoding question

[Carsten Bock]

Hi,

the problem is, the device (a VoLTE phone) will ALWAYS offer AMR-WB and
AMR-NB and we will need to do transcoding to G722 / G711 in most cases
(unless the B-Party actually offers AMR-WB/AMR-NB).
The Answer may be pure G711 (RTPEngine will do Transcoding G711 <=> AMR-WB
[meaningless]) or G722 (RTPEngine will do Transcoding G722 <=> AMR-WB
[Makes sense]) or AMR-NB/-WB (no Transcoding [ideal]). If I could limit the
Answer from RTPEngine to contain only AMR-NB, that would ideal, as AMR-NB
has less complexity, than transcoding into AMR-WB and it would additionally
save bandwidth (which is important in our case).

However, I should mention that I am already more than happy with the
current result. Transcoding is working great, even with AMR/AMR-WB!

Thanks,
Carsten
--
Carsten Bock I Managing Director
ng-voice GmbH

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www.ng-voice.com

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Am Mi., 22. Mai 2019 um 01:17 Uhr schrieb Richard Fuchs <rfuchs at sipwise.com
>:

> 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
>
>
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