Transcoding with RTPengine and Kamailio

I’ve talked a bit in the past about using RTPengine to act as an RTP proxy / media proxy in conjunction with Kamailio.

Recently transcoding support was added to RTPengine, and although the Kamailio rtpengine module doesn’t yet recognise the commands when we put them in, they do work to transcode from one codec to another.

If you’ve setup your RTPengine installation as per this tutorial, and have it working with Kamailio to relay RTP, you can simply change the rtpengine_manage() to add transcoding support.

For example to allow only PCMU calls and transcode anything else we’d change the rtpengine_manage(); to:

rtpengine_manage("codec-mask-all codec-transcode-PCMU");

This will mask all the other codecs and transcode into PCMU, simple as that.

Beware software based transcoding is costly to resources, this works fine in small scale, but if you’re planning on transcoding more than 10 or so streams you’ll start to run into issues, and should look at hardware based transcoding.

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