Installing audio codecs (g729 and friends) for VICIdial

A Codec is how your call's audio gets squeezed onto the wire. VICIdial runs on Asterisk, which ships G.711 codec free and clear. The narrowband codecs people actually ask for — g729 and g723 — are licensed, and that licensing is the part that trips operators up.

G711 versus the narrowband codecs

G711 sounds great and costs nothing in licensing, but it's hungry — roughly 64 kbps of payload per leg before overhead. G.729 codec compresses the same speech to about 8 kbps with a small quality trade. On a box running many concurrent RTP streams, that's the difference between saturating an uplink and having room to spare. G723 squeezes even harder at a bigger quality cost and is rarely worth it today.

Whether you even need g729 depends on your Carrier. If your SIP trunk accepts g711, run g711 and skip the licensing entirely — you only need g729 when the carrier requires it or your bandwidth is tight.

Why g729 needs registration

G729 is a patented codec. The transcoding module isn't part of stock Asterisk for that reason; you add it separately, and a commercial-grade build is per-channel licensed. The free passthrough route — where Asterisk never decodes the audio, just relays g729 between two endpoints that both speak it — needs no transcoding license, and for a dialer that's often all you need, because the carrier and the agent leg agree on g729 end to end.

You only need real transcoding when Asterisk has to convert — for example, mixing a g729 carrier leg with a g711 Webphone, or recording in a format that requires decoding. Each simultaneous transcode then consumes a license channel and CPU. Know which path you're on before you buy anything.

flowchart TD
  A[Carrier offers g729] --> B{Agent endpoint speaks g729}
  B -- yes --> C[Passthrough no transcode license]
  B -- no --> D{Asterisk must convert}
  D -- yes --> E[Transcoding needs g729 module and per channel license]
  D -- no --> F[Fall back to g711 free]
  C --> G[Lower bandwidth call]
  E --> G

Installing the module

Place the codec module where Asterisk loads its modules, match the build to your exact Asterisk version and architecture, and reload. A mismatched module fails to load and logs a clear error at startup — check the CLI for it. Then confirm with the core CLI that g729 shows up in the active codec list; if it's listed, allow it on the relevant SIP peer so the codec gets offered in negotiation.

Two gotchas. The module must match the Asterisk version precisely — a build for the wrong minor release silently refuses to load. And codec order matters: list g729 ahead of g711 in the peer config if you want it preferred, or Asterisk will happily settle on the free one.

The practical recommendation

Start on g711. It's free, it sounds best, and most carriers take it. Reach for g729 only when bandwidth or the carrier forces the issue, and prefer passthrough over transcoding to avoid the per-channel license. Our install guide covers the surrounding Asterisk build, and the Asterisk version compatibility notes matter here because the codec module is version-locked.

On our managed boxes the codecs are configured and the Asterisk build is matched, so g711 works out of the box and g729 is a config change away — provisioned in under 40 seconds, root SSH yours. See plans on our pricing page.