Opus Interactive Audio Codec
Overview

Opus is a totally open, royalty-free, highly versatile audio codec. Opus is unmatched for interactive speech and music transmission over the Internet, but is also intended for storage and streaming applications. It is standardized by the Internet Engineering Task Force (IETF) as RFC 6716 which incorporated technology from Skype’s SILK codec and Xiph.Org’s CELT codec.

Technology

Opus can handle a wide range of audio applications, including Voice over IP, videoconferencing, in-game chat, and even remote live music performances. It can scale from low bit-rate narrowband speech to very high quality stereo music. Supported features are :
Bit-rates from 6 kb/s to 510 kb/s
Sampling rates from 8 kHz (narrowband) to 48 kHz (fullband)
Frame sizes from 2.5 ms to 60 ms
Support for both constant bit-rate (CBR) and variable bit-rate (VBR)
Audio bandwidth from narrowband to fullband
Support for speech and music
Support for mono and stereo
Support for up to 255 channels (multistream frames)
Dynamically adjustable bitrate, audio bandwidth, and frame size
Good loss robustness and packet loss concealment (PLC)
Floating point and fixed-point implementation

You can read the full specification, including the reference implementation, in RFC 6716. An up-to-date implementation of the Opus standard is also available from the downloads page.
News

Opus Standardized as RFC6716, Versions 1.0.0 and 1.0.1 Are Available

11 September, 2012

It’s official, Opus has now been standardized by the IETF as RFC 6716. Along with the RFC are the first stable releases. Version 1.0.0 includes exactly the same source code as the reference implementation in the RFC. Version 1.0.1 also includes minor fixes that were made after the RFC was « frozen ». Both releases are available from the downloads page.

Third Release Candidate for Opus 1.0.1

4 September, 2012

This third release candidate for 1.0.1 has documenation and minor portability fixes as part of the final polish before release. Source code is available from the downloads page.

Second Release Candidate for Opus 1.0.1

15 August, 2012

This second release candidate for 1.0.1 includes documentation fixes and a Windows build system. Source code is available from the archived downloads page.

Release Candidates for Opus 1.0.0 and 1.0.1

8 August, 2012

Release candidates for the upcoming 1.0.0 and 1.0.1 releases are now available. Expect the final 1.0.0 release in the next few weeks along with the final Opus RFC. Version 1.0.1 will be released at the same time and includes minor fixes that did not make it to the RFC. Source code is available from the downloads page.

WebRTC Adopts Opus as MTI Codec

27 July, 2012

Participants to the IETF rtcweb working group have accepted (through typical IETF strong consensus) a proposal to select both Opus and G.711 as mandatory-to-implement (MTI) audio codecs. This means that all browsers that implement that standard will have to ship Opus support.

Opus Ships in Firefox 15 (beta)

19 July, 2012

The latest Firefox beta now ships with support for Opus.

Opus Approved by the IETF

2 July, 2012

The IETF has just approved Opus for publication as an RFC. This should happen in the next few weeks, along with release 1.0.

Opus licensing

Opus has a freely available specification, a BSD-licensed, high-quality reference encoder and decoder, and protective, royalty-free licenses for the required patents. The copyright and patent licenses for Opus are automatically granted to everyone and do not require application or approval. The Opus FAQ has more information on why Opus is freely licensed.

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