c Opus has very low algorithmic delay (typ 22.5 ms) compared to popular music formats such as MP3, Ogg Vorbis, LC-AAC and HE-AAC (all over 100 ms), yet performs very competitively with them in terms of quality per bitrate, making it comparably viable as a storage & playback format. c Opus can seamlessly transition among high and low bitrates, using a linear prediction codec (the SILK layer) at lower bitrates and a lapped transform codec (the CELT layer) at higher bitrates, as well as a hybrid of the two for a short overlap in which SILK encodes the 0–8 kHz spectrum and the CELT layer encodes only the frequencies above 8kHz. Opus incorporates technology from two codecs, the speech-oriented SILK codec developed by Skype and the multi-purpose low-latency CELT codec developed by with significant changes to each to ensure they can work together.

b Opus is also a Mandatory To Implement (MTI) codec for the upcoming WebRTC (Web Real Time Communication) specification of the World Wide Web Consortium (W3C).

Many Software patents which cover Opus are licensed under royalty-free terms.

As an open format standardised through Request for Comments (RFC) 6716, c a high quality reference implementation is provided under the 3-clause BSD license a which compiles and runs on the vast majority of general purpose and embedded (fixed point) processors. Opus is a lossy audio compression format developed by the Internet Engineering Task Force (IETF) designed to be suitable for interactive real-time applications over the Internet, a including music as well as speech, yet it is also very competitive for use as a storage and playback format, being a class leader at around 64 kbps and also at 96 kbps.

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