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Collaboration, Voice & AV · Intermediate

Opus

An open, royalty-free IETF audio codec (RFC 6716) that adapts from 6 to 510 kbps and from narrowband to fullband.

Definition

Opus combines the SILK speech codec and the CELT music codec to scale seamlessly between low-bit-rate speech and high-fidelity music. It supports variable bit rate, frame sizes from 2.5 to 60 ms, in-band forward error correction and strong packet loss concealment. Opus is mandatory in WebRTC and is used by Webex, Cisco IP phones, Expressway and Microsoft Teams among others.

Example

A Webex App call over a congested LTE link drops from 40 kbps to 16 kbps Opus without renegotiation.

Exam tip

Opus is the modern answer for adaptive, loss-resilient, wideband audio; it is variable rate, unlike fixed G.711 or G.729.

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