Codec

Coder-decoder algorithm that compresses and decompresses voice data for VoIP transmission

What is a codec?

A codec (coder-decoder) is an algorithm that compresses voice or video data for transmission over a network and decompresses it at the receiving end. In VoIP, the choice of codec directly impacts call quality, bandwidth consumption, and latency.

Common VoIP codecs

Popular codecs include G.711 (uncompressed, toll quality), G.729 (compressed, low bandwidth), and Opus (adaptive, used in WebRTC). Each trades off between bandwidth efficiency and audio fidelity.

Codec negotiation in softphones

During call setup, SIP endpoints negotiate which codec to use via SDP (Session Description Protocol). Modern softphone platforms support multiple codecs and select the optimal one based on network conditions.