Support for Octet Align

[Zoren Dela Cruz]

Hello,

I am setting up a VoIP-to-VoLTE call using the MicroSIP softphone. MicroSIP advertises support for AMR and AMR-WB codecs in octet-aligned mode.

Could you please clarify how octet alignment should be enabled on RTPengine? Specifically, is octet alignment controlled by RTPengine configuration, or is it determined by the codec negotiation with the VoLTE device?

Thank you,
Zoren

[Richard Fuchs]

On 15/12/2025 19.10, Zoren Dela Cruz wrote:

I am setting up a VoIP-to-VoLTE call using the MicroSIP softphone. MicroSIP advertises support for AMR and AMR-WB codecs in octet-aligned mode.

Could you please clarify how octet alignment should be enabled on RTPengine? Specifically, is octet alignment controlled by RTPengine configuration, or is it determined by the codec negotiation with the VoLTE device?

The details depend on the exact scenario you're working with, but in general there is no need to "enable" octet aligned mode.

For a normal call, codec negotiation happens between end devices, and rtpengine is not involved in the decision making process.

If you instruct rtpengine to transcode from/to AMR, then it depends on whether you're offering or accepting AMR.

If you're accepting an AMR offer from an end device, then the mode (octet aligned or bandwidth efficient) is mandated by the end device, and rtpengine will accept whichever mode was offered. If both are offered, then the first one listed will be accepted, but there are ways to tell rtpengine to prefer one over the other, or even reject one or both.

If you're instructing rtpengine to offer AMR to some end device, then the offer flags determine which mode will be offered. The default is octet aligned, but bandwidth efficient can be used instead, or even both can be offered. If the mode being offered is not supported by the end device, then AMR would likely be rejected.

Cheers

[Avremy Cohen]

how is it possible to offer octet-aligned and bandwidth-efficient modes at the same time , meaning to offer 2 variants of the same codec?  

[Richard Fuchs]

On 04/01/2026 09.05, Avremy Cohen wrote:
> how is it possible to offer octet-aligned and bandwidth-efficient
> modes at the same time , meaning to offer 2 variants of the same codec?

You just tell rtpengine to offer it twice, using two offer/transcode flags.

Note that octet aligned mode is the default if not otherwise specified,
so to offer bandwidth efficient mode, you explicitly have to put
"octet-align=0"

Cheers

[Avremy Cohen]

I Tried that, for some reason it wasnt accepted , 

'internal internal codec-offer-telephone-event codec-mask-all codec-transcode-AMR-WB/16000/1///octet-align--1;mode-change-capability--2;max-red--220 codec-transcode-AMR-WB/16000/1///octet-align--0;mode-change-capability--2;max-red--220 replace-origin ICE=remove RTP/AVP'

I beleive it couldn't do 2 variants of the same codec, is that possible ?

[Richard Fuchs]

On 06/01/2026 09.08, Avremy Cohen wrote:

I Tried that, for some reason it wasnt accepted , 

'internal internal codec-offer-telephone-event codec-mask-all codec-transcode-AMR-WB/16000/1///octet-align--1;mode-change-capability--2;max-red--220 codec-transcode-AMR-WB/16000/1///octet-align--0;mode-change-capability--2;max-red--220 replace-origin ICE=remove RTP/AVP'

I beleive it couldn't do 2 variants of the same codec, is that possible ?

It definitely can do that, and this is how you do it.

What exactly does "it wasn't accepted" mean?

Cheers