Opus is an adaptive codec that provides better audio call quality than G.711/G.729 voice codecs and in a low bandwidth environment. The codec has a very low algorithm delay and is it is highly scalable in terms of audio bandwidth, bitrate, and complexity. Over the recent years, the inclusion of OPUS in various cloud & collaboration deployments has only increased with more and more endpoints & devices supporting the codec.
Why OPUS Transcoding?
There are a lot of deployments that require transcoding between OPUS to other audio codecs to support interoperability in a collaboration design. Some of the use cases are based on the requirements:
Better audio quality to remote works / Contact center Agents ( over VPN)
Need for VBR performance for a large number of WFH Webex calling users
Need for transcoding for calls between enterprise users (IP Phones, Webex clients, UCM Endpoints, etc.) and PSTN callers
To transcode the recorded call leg between an agent IP Phone and a recording server.
OPUS Codec Transcoding
Starting IOS XE 17.6.1 release, transcoding OPUS encoded media streams to other voice codecs is supported for both CUBE based LTI transcoding and CUCM based SCCP transcoding but with the following specifications. It is supported with CUBE version 14.4 or CUCM 14 SU1 release.
IOS XE 17.6.1 marks phase 1 of OPUS transcoding inclusion on IOS XE platforms. In its first phase, only IP to IP flow is supported which covers both OPUS narrowband and wideband codec. Both variable bitrate (VBR) and constant bitrate (CBR) are supported with bitrate ranging from 6kbps to 32kbps.
maxaveragebitrate in SDP to remote is set to 32kbps for CPU & BW efficiency.
Frame size or packet duration can be 10ms,20ms
The existing codec CLI under dspfarm transcoding profile is modified to add a new codec option, opus.
To enable this feature, the admin needs to configure code opus under the dspfarm profile in addition to the existing dspfarm and sccp/LTI configurations.
OPUS Transcoding Scale
The table below shows the OPUS transcoding maximum sessions for each PVDM4 type under regular and universal transcoding dspfarm profile. For better scale calculation please use the DSP calculator.