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Opus (audio format)

Opus
Filename extension
.opus[1]
Internet media typeaudio/ogg[2]
audio/opus (RTP)[3]
Developed byIETF codec working group
Initial releaseSeptember 11, 2012 (2012-09-11)
Type of formatLossy audio
Contained byOgg, Matroska, WebM, MPEG-TS, ISOBMFF, CAF
Extended fromSILK, CELT
StandardRFC 6716
Open format?Yes
Free format?Yes
Websiteopus-codec.org
libopus
Developer(s)Xiph.Org Foundation
Initial releaseAugust 26, 2012 (2012-08-26)
Stable release
1.5.2 / April 12, 2024 (2024-04-12)
Written inC89
PlatformCross-platform
TypeAudio codec, reference implementation
License3-clause BSD license (with patent license)
WebsiteOpus codec downloads

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 embedded processors.[4][5] 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.[6][7]

Opus combines the speech-oriented LPC-based SILK algorithm and the lower-latency MDCT-based CELT algorithm, switching between or combining them as needed for maximal efficiency.[4] 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)[8] necessary for use as part of a real-time communication link, 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.[9]

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.[10] Opus is widely used as a voice over IP (VoIP) codec in applications such as Discord,[11] WhatsApp,[12][13][14] and the PlayStation 4.[15]

  1. ^ "MIME Types and File Extensions". XiphWiki.
  2. ^ Terriberry, Timothy; Lee, Ron; Giles, Ralph (April 2016). "Content Type". Ogg Encapsulation for the Opus Audio Codec. IETF. p. 30. sec. 9. doi:10.17487/RFC7845. RFC 7845. Retrieved 2016-04-30.
  3. ^ Spittka, Julian; Vos, Koen; Valin, Jean-Marc (2015-06-30). "Opus Media Type Registration". RTP Payload Format for the Opus Speech and Audio Codec. IETF. p. 9. sec. 6.1. doi:10.17487/RFC7587. ISSN 2070-1721. RFC 7587. Retrieved 2015-06-30.
  4. ^ a b "Opus Codec". Opus (Home page). Xiph.org Foundation. Retrieved July 31, 2012.
  5. ^ Bright, Peter (2012-09-12). "Newly standardized Opus audio codec fills every role from online chat to music". Ars Technica. Retrieved 2014-05-28.
  6. ^ Cite error: The named reference testsummary was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference 96kListeningTest was invoked but never defined (see the help page).
  8. ^ Jean-Marc Valin; Gregory Maxwell; Timothy B. Terriberry; Koen Vos (October 17–20, 2013). "High-Quality, Low-Delay Music Coding in the Opus Codec" (PDF). www.xiph.org. New York, NY: Xiph.Org Foundation. p. 2. Archived from the original (PDF) on 14 July 2018. Retrieved 19 August 2014. CELT's look-ahead is 2.5 ms, while SILK's look-ahead is 5 ms, plus 1.5 ms for the resampling (including both encoder and decoder resampling). For this reason, the CELT path in the encoder adds a 4 ms delay. However, an application can restrict the encoder to CELT and omit that delay. This reduces the total look-ahead to 2.5 ms.
  9. ^ Chen, Raymond (April 1, 2011). "Opus Testing" (PDF). Retrieved 2016-01-02.
  10. ^ Cite error: The named reference OpusLicense was invoked but never defined (see the help page).
  11. ^ "What Features Does Discord Have?". Discord. Retrieved 2017-10-29.
  12. ^ Cite error: The named reference Register was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference Srivastava was invoked but never defined (see the help page).
  14. ^ Cite error: The named reference Hazra was invoked but never defined (see the help page).
  15. ^ Cite error: The named reference playstation was invoked but never defined (see the help page).

Opus (audio format)

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