Opus codec

Opus

Filename extension	.opus
Internet media type	audio/opus, audio/ogg
Developed by	IETF codec working group
Initial release	September 11, 2012 (2012-09-11)
Type of format	Audio
Contained by	Ogg, Matroska, WebM, MPEG-TS, MP4
Extended from	SILK, CELT
Standard	RFC 6716
Open format?	Yes
Website	opus-codec.org

Opus is a lossy audio coding format developed by the Xiph.Org Foundation and standardized by the Internet Engineering Task Force, designed to efficiently code speech and general audio in a single format, while remaining low-latency enough for real-time interactive communication and low-complexity enough for low-end ARM3 processors. Opus replaces both Vorbis and Speex for new applications, and several blind listening tests have ranked it higher-quality than any other standard audio format at any given bitrate until transparency is reached, including MP3, AAC, and HE-AAC.

Opus combines the speech-oriented linear predictive coding SILK algorithm and the lower-latency, MDCT-based CELT algorithm, switching between or combining them as needed for maximal efficiency. Bitrate, audio bandwidth, complexity, and algorithm can all be adjusted seamlessly in each frame. Opus has the low algorithmic delay (26.5 ms by default) necessary for use as part of a real-time communication link, permitting natural conversation, networked music performances, and live lip sync; by trading-off quality or bitrate, the delay can be reduced down to 5 ms. Its delay is exceptionally low compared to competing codecs, which require well over 100 ms, yet Opus performs very competitively with these formats in terms of quality per bitrate.

As an open format standardized through RFC 6716, a reference implementation called libopus is available under the New BSD License. The reference has both fixed-point and floating-point optimizations for low- and high-end devices, with SIMD optimizations on platforms that support them. All known software patents that cover Opus are licensed under royalty-free terms.