Opus (audio format)

{{short description|Lossy audio coding format}}{{Infobox file format | name = Opus | logo = 150px | caption = | extension = .opus<ref name="MIME-and-FileExt">{{cite web | url = https://wiki.xiph.org/MIME_Types_and_File_Extensions | title = MIME Types and File Extensions | website = XiphWiki }}</ref> |_nomimecode = true | mime = <code>audio/ogg</code><ref name="Ogg">{{cite IETF | title = Ogg Encapsulation for the Opus Audio Codec | rfc = 7845 | sectionname = Content Type | section = 9 | page = 30 | last1 = Terriberry | first1 = Timothy | last2 = Lee | first2 = Ron | last3 = Giles | first3 = Ralph | date = April 2016 | publisher = IETF | access-date = 2016-04-30}}</ref> <code>audio/opus</code> (RTP)<ref name="OpusMIME">{{cite IETF | title = RTP Payload Format for the Opus Speech and Audio Codec | rfc = 7587 | sectionname = Opus Media Type Registration | section = 6.1 | page = 9 | last1 = Spittka | first1 = Julian | last2 = Vos | first2 = Koen | last3 = Valin | first3 = Jean-Marc | date = 2015-06-30 | publisher = IETF | access-date = 2015-06-30 | issn = 2070-1721}}</ref> | owner = IETF [http://www.ietf.org/mailman/listinfo/codec codec] working group | released = {{start date and age|2012|09|11}} | type = Lossy audio | contained by = Ogg, Matroska, WebM, MPEG-TS, ISOBMFF, CAF | extended from = SILK, CELT | extended to = | standard = {{IETF RFC|6716}} | open = Yes | free = Yes | url = {{URL|https://opus-codec.org/}} }}

{{Infobox software | title = libopus | name = libopus | screenshot = 250px | caption = Screenshot of <code>opusinfo</code> showing information of an .opus file | developer = Xiph.Org Foundation | released = {{Start date|2012|08|26}} | latest release version = 1.6 | latest release date = {{Start date and age|2025|12|15}} | repo = {{URL|https://gitlab.xiph.org/xiph/opus}} | programming language = C89 | platform = Cross-platform | genre = Audio codec, reference implementation | license = 3-clause BSD license ({{URL|https://opensource.org/license/bsdpluspatent|with patent license}}) | website = {{URL|https://opus-codec.org/downloads/|Opus codec downloads}} }}

'''Opus''' is a free and open source lossy audio coding format developed by the Xiph.Org Foundation and standardized by the Internet Engineering Task Force, designed for efficient low-latency encoding of both speech and general audio. Due to its lower latency relative to other standard codecs, Opus finds specific use cases in real-time interactive communication for low-end embedded processors.<ref name="homepage">{{cite web |url = https://opus-codec.org/ |title=Opus Codec |work=Opus |publisher=Xiph.org Foundation |type=Home page |access-date=July 31, 2012 }}</ref><ref name="ars-role">{{cite web |url = https://arstechnica.com/gadgets/2012/09/newly-standardized-opus-audio-codec-fills-every-role-from-online-chat-to-music/ |title=Newly standardized Opus audio codec fills every role from online chat to music |first=Peter |last=Bright |work=Ars Technica |date=2012-09-12 |access-date=2014-05-28 }}</ref> Opus replaces both Vorbis and Speex for new applications.

Opus combines the speech-oriented LPC-based SILK algorithm and the lower-latency MDCT-based CELT algorithm and pyramid vector quantization, switching between or combining them as needed.<ref name="homepage" /> Bitrate, audio bandwidth, complexity, and algorithm choice can be adjusted for each individual frame. Opus has low algorithmic delay (26.5 ms by default)<ref name="ValinAES135" />{{rp|p=2}} ideal 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 further reduced down to 5 ms. Its delay thus is significantly lower compared to competing codecs, which require well over 100 ms. Opus remains competitive with these formats in terms of quality per bitrate.<ref name="testing">{{cite web |first=Raymond |last=Chen |url = http://www.ietf.org/proceedings/80/slides/codec-4.pdf |title=Opus Testing |date=April 1, 2011 |access-date=2016-01-02}}</ref>

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.<ref name="OpusLicense"/> Opus is widely used as a voice over IP (VoIP) codec in applications such as Discord,<ref name="What Features Does Discord Have">{{cite web |title=What Features Does Discord Have? |url=https://discordapp.com/features |url-status=dead |access-date=2017-10-29 |website=Discord |language=en-US |archive-date=2017-06-06 |archive-url=https://web.archive.org/web/20170606090311/https://discordapp.com/features }}</ref> WhatsApp,<ref name="Register"/><ref name="Srivastava"/><ref name="Hazra"/> and the PlayStation 4.<ref name="playstation"/> Listening tests have ranked it higher-quality than other standard audio formats at any given bitrate until transparency is reached, including MP3, AAC, and HE-AAC.<ref name="testsummary" /><ref name="96kListeningTest" />

==Features== {{More citations needed section||date=August 2025}}

thumb|left|Possible bitrate and latency combinations compared with other audio formats

Opus supports constant and variable bitrate encoding from 6 kbit/s to 510 kbit/s (or up to 256 kbit/s per channel for multi-channel tracks), frame sizes from 2.5 ms to 60 ms, and five sampling rates from 8 kHz (with 4 kHz bandwidth) to 48 kHz (with 20 kHz bandwidth, the human hearing range). An Opus stream can support up to 255 audio channels, and it allows channel coupling between channels in groups of two using mid-side coding.<ref name="ValinAES135" />{{rp|p=1}}

Opus has very short latency (26.5 ms using the libopus default of 20 ms frames and default application setting), which makes it suitable for real-time applications such as telephony, voice over IP and videoconferencing;<ref name="ars-role" /> research by Xiph led to the CELT codec currently adopted by Opus, which preserved quality while maintaining low delay. In any Opus stream, the bitrate, bandwidth, and delay can be continually varied without introducing any distortion or discontinuity; mixing packets from different streams will cause a smooth non-intrusive change, rather than the distortion common in other codecs. Unlike Vorbis, Opus does not require large codebooks for each individual file, making it relatively more efficient and resilient for short clips of audio.

[[File:FSsongmetal2-Opus-exp7.20120823-sweep.png|thumb|400px|right|Spectrogram of Opus-encoded (~1.0) audio as bitrate rises (~32 to ~160 kbit/s) clearly shows lowpass behavior and better preservation of the band energy with CELT (compare original, Vorbis, MP3, AAC).]]

The Opus format is based on a combination of the full-bandwidth CELT format and the speech-oriented SILK format, both heavily modified: CELT is based on the modified discrete cosine transform (MDCT) that most music codecs use, using CELP techniques in the frequency domain for better prediction, while SILK uses linear predictive coding (LPC) and an optional long-term prediction filter to model speech. In Opus, both were modified to support more frame sizes, as well as further algorithmic improvements and integration, such as using CELT's range encoder for both types. To minimize overhead at low bitrates, if latency is not as pressing, SILK has support for packing multiple 20 ms frames together, sharing context and headers; SILK also allows Low Bitrate Redundancy (LBRR) frames, allowing low-quality packet loss recovery. CELT includes both spectral replication and noise generation, similar to AAC's SBR and PNS, and can further save bits by filtering out all harmonics of tonal sounds entirely, then replicating them in the decoder.<ref>{{cite web |url=https://people.xiph.org/~xiphmont/demo/celt/demo.html |title=next generation audio: CELT update 20101223 |date=December 23, 2010 |first=Christopher |last=Montgomery |author-link=Chris Montgomery}}</ref> Better tone detection is an ongoing project to improve quality.

The format has three different modes: speech, hybrid, and CELT. When compressing speech, SILK is used for audio frequencies up to 8 kHz. If wider bandwidth is desired, a hybrid mode uses CELT to encode the frequency range above 8 kHz. The third mode is pure-CELT, designed for general audio. SILK is inherently VBR and cannot hit a bitrate target, while CELT can always be encoded to any specific number of bytes, enabling hybrid and CELT mode when CBR is required.

SILK supports frame sizes of 10, 20, 40 and 60 ms. CELT supports frame sizes of 2.5, 5, 10 and 20 ms. Thus, hybrid mode only supports frame sizes of 10 and 20 ms; frames shorter than 10 ms will always use CELT mode. A typical Opus packet contains a single frame, but packets of up to 120 ms are produced by combining multiple frames per packet. Opus can transparently switch between modes, frame sizes, bandwidths, and channel counts on a per-packet basis, although specific applications may choose to limit this.

The reference implementation is written in C and compiles on hardware architectures with or without a floating-point unit, although floating-point is currently required for audio bandwidth detection (dynamic switching between SILK, CELT, and hybrid encoding) and most speed optimizations.

===Containers=== Opus packets are not self-delimiting, but are designed to be used inside a container of some sort which supplies the decoder with each packet's length. Opus was originally specified for encapsulation in Ogg containers, specified as <code>audio/ogg; codecs=opus</code>, and for Ogg Opus files the <code>.opus</code> filename extension is recommended.<ref name="Ogg" /> Opus streams are also supported in Matroska,<ref name="Matroska">{{cite mailing list |url=http://lists.matroska.org/pipermail/matroska-users/2013-September/006883.html |title=MKVToolNix v6.4.0 released |first=Moritz |last=Bunkus |mailing-list=Matroska users |date=2013-09-16 |access-date=2013-12-24}}</ref> WebM,<ref name=webm-guidelines>{{cite web|title=WebM Container Guidelines|url=http://www.webmproject.org/docs/container/|website=The WebM Project|access-date=19 October 2015}}</ref> MPEG-TS,<ref name="mpeg-ts">{{cite web |url=https://smpte-ra.org/registered-mpeg-ts-ids |title=List of Registered MPEG TS Identifiers – SMPTE Registration Authority, LLC |date=2019-01-05 |publisher=SMPTE |access-date=2019-01-05}}</ref> and MP4.<ref>{{cite web |url=https://vfrmaniac.fushizen.eu/contents/opus_in_isobmff.html |title=Encapsulation of Opus in ISO Base Media File Format |date=2018-08-28 |access-date=2019-01-05 |archive-date=2019-01-06 |archive-url=https://web.archive.org/web/20190106204303/https://vfrmaniac.fushizen.eu/contents/opus_in_isobmff.html |url-status=dead }}</ref>

Alternatively, each Opus packet may be wrapped in a network packet which supplies the packet length. Opus packets may be sent over an ordered datagram protocol such as RTP.<ref>{{cite IETF |title=RTP Payload Format for the Opus Speech and Audio Codec |rfc=7587 |last1=Spittka |first1=Julian |last2=Vos |first2=Koen |last3=Valin |first3=Jean-Marc |date=2015-06-30 |issn=2070-1721 |publisher=IETF |access-date=2019-01-05}}</ref>

An optional self-delimited packet format is defined in an appendix to the specification.<ref>{{cite IETF |title=Definition of the Opus Audio Codec |rfc=6716 |sectionname=Self-Delimiting Framing |appendix=B |page=321 |last1=Valin |first1=Jean-Marc |last2=Vos |first2=Koen |last3=Terriberry |first3=Timothy B. |date=2012-09-11 |issn=2070-1721 |publisher=IETF |access-date=2019-01-05}}</ref> This uses one or two additional bytes per packet to encode the packet length, allowing packets to be concatenated without encapsulation.

===Bandwidth and sampling rate=== {{see also|Voice frequency|Wideband audio}} Opus allows the following bandwidths during encoding. Opus compression does not depend on the input sample rate; timestamps are measured in 48 kHz units even if the full bandwidth is not used. Likewise, the output sample rate may be freely chosen. For example, audio can be input at 16 kHz yet be set to encode only narrowband audio.<ref name="rfc-sample_rates">{{cite IETF |title=Definition of the Opus Audio Codec |rfc=6716 |sectionname=Opus Codec Overview |section=2 |page=8 |last1=Valin |first1=Jean-Marc |last2=Vos |first2=Koen |last3=Terriberry |first3=Timothy B. |date=2012-09-11 |access-date=2014-06-21 |issn=2070-1721}}</ref> Version 1.6 introduced an experimental build flag that enables a feature known as Opus HD, allowing sampling rates of up to 96 kHz for non-audio purposes.<ref name=":1" />

{| class="wikitable" style="text-align:center;" |- ! Abbreviation ! Audio bandwidth ! Effective sample rate |- |style="text-align:left;"| NB (narrowband) | {{0}}4 kHz | {{0}}8 kHz |- |style="text-align:left;"| MB (medium-band){{NoteTag|Unused by default since 1.3.}} | {{0}}6 kHz | 12 kHz |- |style="text-align:left;"| WB (wideband) | {{0}}8 kHz | 16 kHz |- |style="text-align:left;"| SWB (super-wideband) | 12 kHz | 24 kHz |- |style="text-align:left;"| FB (fullband){{NoteTag|Opus cuts audio above 20 kHz, the generally accepted upper limit of the human hearing range.}} | 20 kHz | 48 kHz |}

== History == {{See also|CELT#History|SILK#History}}

Opus was proposed for the standardization of a new audio format at the IETF, which was eventually accepted and granted by the ''codec'' working group. It is based on two initially separate standard proposals from the Xiph.Org Foundation and Skype Technologies S.A. (now Microsoft). Its main developers are Jean-Marc Valin (Xiph.Org, Octasic, Mozilla Corporation, Amazon), Koen Vos (Skype), and Timothy B. Terriberry (Xiph.Org, Mozilla Corporation, Amazon). Among others, Juin-Hwey (Raymond) Chen (Broadcom), Gregory Maxwell (Xiph.Org, Wikimedia), and Chris Montgomery (Xiph.Org) were also involved.

The development of the CELT part of the format originated from discussions on a successor for Vorbis under the working name ''Ghost''. As a newer speech codec from the Xiph.Org Foundation, Opus replaces Xiph's older speech codec Speex, an earlier project of Jean-Marc Valin. CELT has been worked on since November 2007.

The SILK part has been under development at Skype since January 2007 as the successor of their SVOPC, an internal project to make the company independent from third-party codecs like iSAC and iLBC and respective license payments.

In March 2009, Skype suggested the development and standardization of a wideband audio format within the IETF. Nearly a year passed with much debate on the formation of an appropriate working group.<ref name="WGformation">{{cite web |url = http://www.h-online.com/open/news/item/IETF-working-towards-royalty-free-audio-codec-859394.html |title = IETF working towards royalty-free audio codec |publisher=H-online.com |date=2009-11-13 |access-date=2016-04-07}}</ref> Representatives of several companies which were taking part in the standardization of patent-encumbered competing format, including Polycom and Ericsson—the creators and licensors of G.719—as well as France Télécom, Huawei and the Orange Labs (department of France Télécom), which were involved in the creation of G.718, stated objections against the start of the standardization process for a royalty-free format. (Some of the opponents would later claim patent rights that Xiph dismissed; see below.)<ref>{{cite web |title=Xiph.org's "Monty" on codecs and patents [LWN.net] |url=https://lwn.net/Articles/465234/ |website=lwn.net}}</ref> The working group finally formed in February 2010, and even the corresponding Study Group 16 from the ITU-T pledged to support its work.

In July 2010, a prototype of a hybrid format was presented that combined the two proposed format candidates SILK and CELT. In September 2010, Opus was submitted to the IETF as proposal for standardization. For a short time the format went under the name of ''Harmony'' before it got its present name in October 2010.<ref name="renaming">{{cite mailing list |url=http://www.ietf.org/mail-archive/web/codec/current/msg01852.html |title=Harmony became Opus |date=2010-10-15 |access-date=2016-01-03 |mailing-list=codec |publisher=IETF |last=Vos |first=Koen}}</ref> At the beginning of February 2011, the bitstream format was tentatively frozen, subject to last changes.<ref name="pre-freeze">{{cite web |url = http://www.hydrogenaud.io/forums/?showtopic=86580 |title=IETF Opus codec now ready for testing |publisher=Hydrogenaudio |access-date=2012-09-12 }}</ref> Near the end of July 2011, Jean-Marc Valin was hired by the Mozilla Corporation to continue working on Opus.<ref name="job">{{cite web |url = http://jmspeex.livejournal.com/7352.html |first = Jean-Marc |last = Valin |title = IETF update, Mozilla |website = LiveJournal.com |date=2011-08-01 |access-date=2012-10-05 }}</ref>

=== Finalization (1.0)=== In November 2011, the working group issued the last call for changes on the bitstream format. The bitstream has been frozen since January 8, 2012.<ref name="bitstream frozen">{{cite web |url = https://www.opus-codec.org/downloads/ |title=Opus Codec |publisher=Xiph.org Foundation |access-date=2012-09-12 }}</ref> On July 2, 2012, Opus was approved by the IETF for standardization.<ref name="jmvalin">{{cite web |url = http://jmspeex.livejournal.com/10981.html |title=Opus approved by the IETF |publisher=Jmspeex.livejournal.com |date=2012-07-03 |access-date=2012-09-12}}</ref> The reference software entered release candidate state on August 8, 2012.<ref name="RC">{{cite mailing list |url=http://lists.xiph.org/pipermail/opus/2012-August/001657.html |title=[opus] Release candidates for 1.0.0 and 1.0.1 are available |publisher=Xiph.org Foundation |mailing-list=opus |access-date=2012-10-05}}</ref> The final specification was released as RFC 6716 on September 10, 2012.<ref name="MozillaHacks2">{{cite web|url=https://hacks.mozilla.org/2012/09/its-opus-it-rocks-and-now-its-an-audio-codec-standard/ |title=It's Opus, it rocks and now it's an audio codec standard! |publisher=Mozilla Hacks |access-date=2012-09-12}}</ref><ref name="ietf-announce">{{cite mailing list |url=http://www.ietf.org/mail-archive/web/ietf-announce/current/msg10682.html |mailing-list=announce |title=RFC 6716 on Definition of the Opus Audio Codec |publisher=IETF |access-date=2012-09-12}}</ref> and versions 1.0 and 1.0.1 of the reference implementation libopus were released the day after.

On July 11, 2013, libopus 1.0.3 brought bug fixes and a new surround sound API that improves channel allocation and quality, especially for LFE.<ref name=opus11>{{cite web |url=http://people.xiph.org/~xiphmont/demo/opus/demo3.shtml |title=Opus update 20131205: 1.1 Release |author1=Monty |first2=Jean-Marc |last2=Valin |access-date=2013-07-17 |archive-date=2017-04-30 |archive-url=https://web.archive.org/web/20170430223047/https://people.xiph.org/~xiphmont/demo/opus/demo3.shtml |url-status=dead }}</ref>

===1.1=== On December 5, 2013, libopus 1.1 was released,<ref name=opus11/> incorporating overall speed improvements and significant encoder quality improvements: Tonality estimation boosts bitrate and quality for previously [http://listening-tests.hydrogenaud.io/igorc/Public%20Multiformat%20Listening%20Test%20@%2064kbps.htm problematic samples], like harpsichords; automated speech/music detection improves quality in mixed audio; mid-side stereo reduces the bitrate needs of many songs; band precision boosting for improved transients; and DC rejection below 3 Hz. Two new VBR modes were added: unconstrained for more consistent quality, and temporal VBR that boosts louder frames and generally improves quality.

libopus 1.1.1 was released on November 26, 2015, and 1.1.2 on January 12, 2016, both adding speed optimizations and bug fixes. July 15, 2016 saw the release of version 1.1.3 and includes bug fixes, optimizations, documentation updates and experimental Ambisonics work.

===1.2=== libopus 1.2 Beta was released on May 24, 2017. libopus 1.2 was released on June 20, 2017.<ref>{{cite web|url=https://opus-codec.org/release/stable/2017/06/20/libopus-1_2.html |title=libopus 1.2 – Opus Codec |publisher=Opus-codec.org |date=2017-06-20 |access-date=2017-08-23}}</ref> Improvements brought in 1.2 allow it to create fullband music at bitrates as low as 32 kbit/s, and wideband speech at just 12 kbit/s.<ref name="XDA Opus 1.2" />

libopus 1.2 includes optional support for the decoder specification changes made in drafts of <nowiki>RFC 8251</nowiki>, improving the quality of output from such low-rate streams.<ref>{{cite web |url=https://people.xiph.org/~jm/opus/opus-1.2/ |title=Opus 1.2 released |first=Jean-Marc |last=Valin |date=2017-06-20}}</ref>

===1.3=== libopus 1.3 was released on October 18, 2018.<ref>{{cite web|url=https://www.opus-codec.org/|title=Opus Codec|website=www.opus-codec.org|access-date=2018-10-22}}</ref> The Opus 1.3 major release again brings quality improvements, new features, and bug fixes.<ref>{{cite web|url=https://people.xiph.org/~jm/opus/opus-1.3/|title=Opus 1.3 Released|website=people.xiph.org|language=en|access-date=2018-10-22}}</ref> Changes since 1.2.x include:

* Improvements to voice activity detection (VAD) and speech/music classification using a recurrent neural network (RNN) * Support for ambisonics coding using channel mapping families 2 and 3 * Improvements to stereo speech coding at low bitrate * Using wideband speech encoding down to 9 kbit/s (mediumband is no longer used) * Making it possible to use SILK down to bitrates around 5 kbit/s * Minor quality improvement on tones * Enabling the spec fixes in <nowiki>RFC 8251</nowiki> by default * Security/hardening improvements

Notable bug fixes include: * Fixes to the CELT PLC * Bandwidth detection fixes

====1.3.1==== libopus 1.3.1 was released on April 12, 2019.<ref>{{cite web|url=https://www.opus-codec.org/|title=Opus Codec|website=www.opus-codec.org|access-date=2019-04-12}}</ref> This Opus 1.3.1 minor release fixes an issue with the analysis on files with digital silence (all zeros), especially on x87 builds (mostly affects 32-bit builds). It also includes two new features: * A new OPUS_GET_IN_DTX query to know if the encoder is in DTX mode (last frame was either a comfort noise frame or not encoded at all) * A new (and still experimental) CMake-based build system that is eventually meant to replace the VS2015 build system (the autotools build system will stay)

=== 1.4 ===

libopus 1.4 was released on April 20, 2023.<ref>{{cite web |url=https://github.com/xiph/opus/releases/tag/v1.4 |title=Opus release 1.4 |website=GitHub |date=2023-04-20 }}</ref> Opus 1.4 brings the following improvements and fixes:

* Improved tuning of the Opus in-band FEC called LBRR (Low-bitrate redundancy)<ref>{{cite web|url=https://www.amazon.science/blog/neural-encoding-enables-more-efficient-recovery-of-lost-audio-packets|title=Neural encoding enables more-efficient recovery of lost audio packets|date=24 March 2023 |access-date=2023-04-20}} ''Article cited for description of LBRR only. Neural FEC is not part of Opus 1.4.''</ref> which previously was causing a significant drop in audio quality under certain circumstances<ref>{{cite web |last=Danahy |first=Scott |title=Subjective Quality Issue: Complexity and FEC |url=https://gitlab.xiph.org/xiph/opus/-/issues/2360 |date=July 20, 2022 }}</ref> * Added a OPUS_SET_INBAND_FEC(2) option that turns on FEC, but does not force SILK mode (FEC will be disabled in CELT mode) * Improved tuning and various fixes to DTX * Added Meson support, improved CMake support

=== 1.5 === libopus 1.5 was released on March 4, 2024.<ref>{{cite web|url=https://opus-codec.org/demo/opus-1.5/ |title=Opus 1.5 Released |date=2024-03-04 |access-date=2024-03-04}}</ref> It added the following backward-compatible improvements:

* Improved packet loss concealment using a deep neural network. * Improved redundancy to prevent packet loss using a rate-distortion-optimized variational autoencoder. * Improved concealment of coding artifacts by adjusting post-filter coefficients using a deep neural network. * Support for additional SIMD CPU instructions; AVX2 on x86-64 and NEON on Aarch64.

=== 1.6 === libopus 1.6 was released on December 15, 2025.<ref name=":1">{{cite web|url=https://opus-codec.org/demo/opus-1.6/ |title=Opus 1.6 Released |date=2025-12-15 |access-date=2025-12-17}}</ref> It added the following backward-compatible improvements:

* A new wideband-to-fullband bandwidth extension (BWE) module * Experimental and optional support for 96 kHz audio with Opus HD * Significant improvement to Deep Redundancy (DRED) * A new 24-bit encoder/decoder API

=== Current development === The codec is under active development.<ref>{{Cite web |title=Commits · xiph/opus |url=https://github.com/xiph/opus |access-date=2024-03-03 |website=GitHub |language=en}}</ref> The current focus is on adding a deep learning based redundancy encoder that enhances packet loss concealment by embedding one second of recovery data in each encoded packet. The deep redundancy (DRED) algorithm was developed by among others Jean-Marc Valin, Ahmed Mustafa, Jan Büthe, Timothy Terriberry, Chris Montgomery, Michael Klingbeil, and Paris Smaragdis from Amazon Web Services<ref>{{Cite web |title=opus/dnn/README.md at main · xiph/opus |url=https://github.com/xiph/opus/blob/main/dnn/README.md |access-date=2024-03-03 |website=GitHub |language=en}}</ref> with sponsorship to open source the algorithm and subsequently extend the IETF standard from Sid Rao.<ref>{{Cite web |title=RTC @Scale 2023 |url=https://atscaleconference.com/events/rtc-scale-2023/ |access-date=2024-03-03 |website=At Scale Conferences |language=en-US}}</ref> This encoder is a backwards compatible change to the codec enabling customers to easily upgrade applications to take advantage of this machine learning capability. A [https://datatracker.ietf.org/doc/draft-ietf-mlcodec-opus-extension/ draft RFC] is underway to standardize the new capability.<ref>{{Cite report |url=https://datatracker.ietf.org/doc/draft-ietf-mlcodec-opus-extension/ |title=Extension Formatting for the Opus Codec |last1=Terriberry |first1=Timothy B. |last2=Valin |first2=Jean-Marc |date=2023-10-23 |publisher=Internet Engineering Task Force |issue=draft-ietf-mlcodec-opus-extension-01}}</ref> This RFC is one of the first attempts to standardize a deep learning algorithm in the IETF.

==Quality comparison and low-latency performance== thumb|360px|Comparison of coding efficiency between Opus and other popular audio formats

Opus performs relatively well at both low and high bitrates.<ref name="testing" />

{{listen|filename=Test mp3 opus 16kbps.wav|title=Comparison between MP3 and Opus|description=The first is an uncompressed WAV file, the second is an MP3 file encoded at 16 kbit/s using LAME, and the third is an Opus file encoded at 16 kbit/s.}} In listening tests around 64 kbit/s, Opus shows superior quality compared to HE-AAC codecs, which were previously dominant due to their use of the patented spectral band replication (SBR) technology.<ref name="slashdot">[http://news.slashdot.org/story/11/04/14/2345238 Next-Gen Low-Latency Open Codec Beats HE-AAC], Slashdot-Meldung vom 14. April 2011.</ref><ref name="testsummary">{{cite news|last1=Valin|first1=Jean-Marc|last2=Vos|first2=Koen|last3=Skoglund|first3=Jan|date=2013-05-17|editor-last=Hoene|editor-first=Christian|title=Summary of Opus listening test results|newspaper=Ietf Datatracker |url=https://datatracker.ietf.org/doc/html/draft-ietf-codec-results-03|url-status=live|archive-url=https://web.archive.org/web/20210724010424/https://datatracker.ietf.org/doc/html/draft-ietf-codec-results-03|archive-date=2021-07-24|access-date=2021-07-24|publisher=Internet Engineering Task Force}}</ref> In listening tests around 96 kbit/s, Opus shows slightly superior quality compared to AAC and significantly better quality compared to Vorbis and MP3.<ref name="96kListeningTest">{{cite web |url=http://listening-test.coresv.net/results.htm |title=Results of the public multiformat listening test |date=July 2014 |author=Kamedo2}}</ref><ref name="quality64">{{cite web |url=http://people.xiph.org/~greg/opus/ha2011/ |title=64kbit/sec stereo multiformat listening test — unofficial results page |first=Gregory |last=Maxwell |year=2011 |publisher=Xiph.Org Foundation |access-date=2011-06-19 |archive-date=2012-11-12 |archive-url=https://web.archive.org/web/20121112232722/http://people.xiph.org/~greg/opus/ha2011/ |url-status=dead }}</ref>

Opus has very low algorithmic delay,<ref name="homepage" /> a necessity for use as part of a low-audio-latency communication link, which can permit natural conversation, networked music performances, or lip sync at live events. Total algorithmic delay for an audio format is the sum of delays that must be incurred in the encoder and the decoder of a live audio stream regardless of processing speed and transmission speed, such as buffering audio samples into blocks or frames, allowing for window overlap and possibly allowing for noise-shaping look-ahead in a decoder and any other forms of look-ahead, or for an MP3 encoder, the use of bit reservoir.<ref name="algdelay">{{cite journal|last1=Lutzky|first1=Manfred|last2=Schuller|first2=Gerald|last3=Gayer|first3=Marc|last4=Krämer|first4=Ulrich|last5=Wabnik|first5=Stefan|title=A guideline to audio codec delay|journal=In AES 116th Convention, Berlin, Germany|year=2004|pages=8–11|url=https://www.iis.fraunhofer.de/content/dam/iis/de/doc/ame/conference/AES-116-Convention_guideline-to-audio-codec-delay_AES116.pdf|access-date=21 December 2016}}</ref>

Total one-way latency below 150 ms is the preferred target of most VoIP systems<ref name=VoIPlatency>{{cite book|last1=Lironi|first1=F.|last2=Masseroni|first2=C.|last3=Trivisonno|first3=R.|last4=Ball|first4=C. F.|title=VTC-2005-Fall. 2005 IEEE 62nd Vehicular Technology Conference, 2005 |chapter=Multi RAB-based multimedia services over GERAN mobile networks |year=2005|volume=3|pages=1662–1666|doi=10.1109/VETECF.2005.1558224|isbn=0-7803-9152-7|s2cid=44037728}}</ref> to enable natural conversation with turn-taking little affected by delay. Musicians typically feel in-time with up to around 30 ms audio latency,<ref name="musiclatency">{{cite book|last1=Lago|first1=Nelson Posse|last2=Kon|first2=Fabio|chapter=The quest for low latency|title=Proceedings of the International Computer Music Conference 2004|date=November 2004|pages=33–36|chapter-url=https://www.researchgate.net/publication/2876736|access-date=23 April 2019|hdl=2027/spo.bbp2372.2004.142}}</ref> roughly in accord with the fusion time of the Haas effect, though matching playback delay of each user's own instrument to the round-trip latency can also help.<ref name="carot">{{cite book|last=Carôt|first=Alexander|title="Low Latency Audio Streaming for Internet-Based Musical Interaction" in Streaming Media Architectures: Techniques and Applications: Recent Advances|year=2010|publisher=IGI Global|isbn=978-1-61692-833-9|pages=362–383|url=https://books.google.com/books?id=Cb4dWYVJ_8AC&q=Carot+2006+audio+delay&pg=PA362}}</ref> It is suggested for lip sync that around 45–100 ms audio latency may be acceptable.<ref name="lipsync">{{cite conference|first1=Nong|last1=Ye|first2=Yan|last2=Chen|first3=Toni|last3=Farley|title=Qos Requirements Of Multimedia Data On Computer Networks|work=Proceedings of the Second International Conference on Active Media Technology|location=Chongqing, PR China|date=29–31 May 2003|publisher=World Scientific Publishing Company Incorporated|isbn=978-981-238-343-3|pages=183–189|url=https://books.google.com/books?id=UJBMYx_8_2UC&pg=PA183}}</ref>

Opus permits trading-off reduced quality or increased bitrate to achieve an even smaller algorithmic delay (5.0 ms minimum).<ref name="latencyBitrateTradeoff">{{cite web|last=Montgomery|first=Christopher|title=A quick showcase of the bleeding edge... CELT 0.10.0 @ constant PEAQ value, varying latency|url=http://people.xiph.org/~xiphmont/demo/celt/demo.html#demo|work=CELT v0.10 (latest prior to Opus integration)|publisher=xiph.org|access-date=30 October 2012|archive-date=23 August 2013|archive-url=https://web.archive.org/web/20130823153533/http://people.xiph.org/~xiphmont/demo/celt/demo.html#demo|url-status=dead}}</ref> While the reference implementation's default Opus frame is 20.0 ms long, the SILK layer requires a further 5.0 ms lookahead plus 1.5 ms for resampling, giving a default delay of 26.5 ms. When the CELT layer is active, it requires 2.5 ms lookahead for window overlap to which a matching delay of 4.0 ms is added by default to synchronize with the SILK layer. If the encoder is instantiated in the special ''restricted low delay'' mode, the 4.0 ms matching delay is removed and the SILK layer is disabled, permitting the minimal algorithmic delay of 5.0 ms.<ref name="ValinAES135" />{{rp|p=2}}

==Support== The format and algorithms are openly documented and the reference implementation is published as free software. Xiph's reference implementation is called ''libopus'' and a package called ''opus-tools'' provides command-line encoder and decoder utilities. It is published under the terms of a BSD-like license. It is written in C and can be compiled for hardware architectures with or without a floating-point unit. The accompanying diagnostic tool ''opusinfo'' reports detailed technical information about Opus files, including information on the standard compliance of the bitstream format. It is based on ''ogginfo'' from the ''vorbis-tools'' and therefore — unlike the encoder and decoder — is available under the terms of version 2 of the GPL.

===Implementations=== {{IETF RFC|6716}} contains a complete source code for an older version of the reference implementation written in C. RFC {{IETF RFC|8251|plainlink=y}} contains errata. Libopus is the more up-to-date but non-normative branch of the reference implementation.

The FFmpeg project<ref>{{cite web|url=http://git.videolan.org/?p=ffmpeg.git;a=commit;h=5f47c85e5c961d5985a01e16697439d179b03a0e |title=opus: add a native Opus encoder |first=Rostislav |last=Pehlivanov |publisher=Git.videolan.org |date=11 February 2017 |access-date=2017-08-23}}</ref> has encoder and decoder implementations not derived from the reference library. The documentation describes it as CELT-only and poorer-quality than the reference.<ref>{{cite web |title=FFmpeg Codecs Documentation |url=https://ffmpeg.org/ffmpeg-codecs.html#opus |website=ffmpeg.org}}</ref>

The libopus reference library has been ported to C#, Java and Go as part of a project called Concentus. These ports sacrifice performance for the sake of being easily integrated into cross-platform applications.<ref>{{cite web|url=https://github.com/lostromb/concentus |title=lostromb/concentus: Pure portable C#/Java/Golang implementations of the Opus audio codec |publisher=GitHub |access-date=2026-02-27}}</ref>

===Software and content providers=== {{See also|Comparison of VoIP software}}

Digital Radio Mondiale – a digital radio format for AM frequencies – can broadcast and receive Opus audio (albeit not recognised in official standard) using Dream software-defined radio.

The Wikimedia Foundation sponsored a free and open source online JavaScript Opus encoder for browsers supporting the required HTML5 features.<ref name="javascript-opus">{{cite web|url=https://blog.rillke.com/opusenc.js/|title=JavaScript opus encoder|first=Rainer|last=Rillke|date=2015|access-date=2015-02-09}}</ref>

A list of radio stations that stream using Opus audio codec can be found on the Xiph.Org Foundation Icecast directory.<ref>{{Cite web|title=Xiph Directory — Codec Opus|url=https://dir.xiph.org/codecs/Opus|website=Xiph Directory|language=en}}</ref>

In late 2014 and 2015, Google's video platform YouTube started offering Opus audio along with VP9 video in the WebM file format, through DASH streaming.<ref>{{Cite web|title=A look into YouTube's video file anatomy|url=https://youtube-eng.googleblog.com/2016/04/a-look-into-youtubes-video-file-anatomy.html|website=YouTube Engineering and Developers Blog|language=en|access-date=2022-06-10|archive-date=2021-03-08|archive-url=https://web.archive.org/web/20210308172722/https://youtube-eng.googleblog.com/2016/04/a-look-into-youtubes-video-file-anatomy.html|url-status=dead}}</ref> In July 2024, YouTube rolled out an additional high quality audio format option, 256 kbit/s Opus, to YouTube Music Premium subscribers.<ref name="youtube-format-ids-2024-july">{{cite web | title = Youtube Format IDs | url = https://gist.github.com/MartinEesmaa/2f4b261cb90a47e9c41ba115a011a4aa |website=GitHub}}</ref>

Since 2016, WhatsApp has been using Opus as its audio file format.<ref>{{Cite web|last=Rashad|first=A.|date=2017-05-18|title=Audio Manager for WhatsApp: How to play WhatsApp audio messages in music player?|url=https://medium.com/@arashad_777/audio-manager-for-whatsapp-how-to-play-whatsapp-audio-messages-in-music-player-fde42489e5f1|access-date=2020-09-09|website=Medium|language=en}}</ref>

Signal switched from Speex to Opus audio codec for better audio quality in the beginning of 2017.

In 2018, SoundCloud switched from MP3 to Opus, reducing half of its required bandwidth for music streaming.<ref>{{Cite web|title=What is Opus? Here's all you need to know about SoundCloud's new audio file format|url=https://www.factmag.com/2018/01/05/what-is-opus-audio/|website=Fact Magazine|date=5 January 2018 |language=en}}</ref>

In January 2021, Vimeo introduced Opus to its video platform.<ref>{{Cite web|title=Introducing Opus, a powerful new audio codec|url=https://vimeo.com/blog/post/what-is-a-codec-audio-video-explained/|website=vimeo blog|date=12 January 2021 |language=en}}</ref>

In 2021, the Danish journalism website Zetland switched from MP3 to Opus for its articles' audio recordings, which attained a 35 percent reduction in bandwidth and reduced climate footprint.<ref>{{Cite web|title=Audio formats and their climate footprint|url=https://sustainableweb.dk/en/audio-formats/|website=Sustainable Web|date=2 February 2022 |language=en}}</ref><ref>{{Cite web|title=How a tip from a member made our audio files 35 percent greener|url=https://www.zetland.dk/historie/sO9kyxkv-mowGPqpz-7c77c|website=Zetland|date=25 November 2021 |language=da}}</ref>

====Operating system support==== Most end-user software relies on multimedia frameworks provided by the operating system. Native Opus codec support is implemented in most major multimedia frameworks for Unix-like operating systems, including GStreamer, FFmpeg, and Libav libraries.<ref name="gstreamer">{{cite web|url=http://gstreamer.freedesktop.org/news/#2012-02-21T14:00:00Z |title=GStreamer: news |publisher=Gstreamer.freedesktop.org |access-date=2012-10-05}}</ref><ref name="ffmpeg">{{cite web |url=http://ffmpeg.org/general.html#Audio-Codecs |title=Audio Codecs |work=FFmpeg General Documentation |access-date=2014-05-28}}</ref><ref name="libav">{{cite web |url=http://libav.org/general.html#Audio-Codecs |title=Audio Codecs |work=Libav General Documentation |access-date=2014-05-28 |archive-date=2014-05-29 |archive-url=https://web.archive.org/web/20140529051653/http://libav.org/general.html#Audio-Codecs |url-status=dead }}</ref>

The WebM container <code>.webm</code> is mostly used on online video platforms (e.g. YouTube), and is usually treated as a video file by operating systems & media players. Even if a WebM file contains only Opus audio and no video, some music players do not recognize WebM files as audio files and do not support reading of file metadata.<ref>{{Cite web|url=https://hydrogenaud.io/index.php?topic=116054.0|title=Recommended container/extension for opus for tagging compatibility|website=hydrogenaud.io}}</ref>

The Ogg container <code>.opus</code> is preferred for audio-only files, and most media players have support for audio file metadata tagged in the Vorbis comment format.

Google added native support for Opus audio playback in Android 5.0 "Lollipop".<ref name="android dev">{{cite web|author=Google |url=http://developer.android.com/about/versions/lollipop.html | title=Android Lollipop |access-date=2015-11-03}}</ref> However, it was limited to Opus audio encapsulated in Matroska and WebM containers, such as <code>.mkv</code>, <code>.mka</code> and <code>.webm</code> files.<ref name="Android Developers">{{cite web|url=http://developer.android.com/guide/appendix/media-formats.html |title=Supported Media Formats |access-date=2015-04-29}}</ref><ref name="android opus bug">{{cite web|author=Google |url=https://code.google.com/p/android/issues/detail?id=80729 | title= Issue 80729: Opus support not working. |access-date=2016-04-19}}</ref> Android 7.0 "Nougat" introduced support for Opus audio encapsulated in Ogg containers.<ref name="Android-Supported-File-Ext" /> Android 10 finally added native support for <code>.opus</code> extensions.<ref name=":0">{{Cite web|url=https://issuetracker.google.com/issues/37054258|title=Google Issue Tracker|website=issuetracker.google.com}}</ref>

Due to the addition of WebRTC support in Apple's WebKit rendering engine, macOS High Sierra and iOS 11 were released with native playback support for Opus audio encapsulated in Core Audio Format containers.<ref>{{Cite web |url=https://hetzel.net/2017-06-12/ios-11-opus-support-in-podcast-feeds/ |title=iOS 11: Opus support in podcast feeds |access-date=2017-06-25 |archive-date=2018-08-02 |archive-url=https://web.archive.org/web/20180802102121/https://hetzel.net/2017-06-12/ios-11-opus-support-in-podcast-feeds/ |url-status=dead }}</ref> macOS Sonoma added support for mono and stereo Opus audio encapsulated in MPEG-4 and WebM containers in Safari.<ref name="safari-17-notes">{{cite web |url=https://developer.apple.com/documentation/safari-release-notes/safari-17-release-notes |title=Safari 17 Release Notes |website=Apple Developer}}</ref><ref name="webkit-17-blog">{{cite web |url=https://webkit.org/blog/14445/webkit-features-in-safari-17-0/ |title=WebKit Features in Safari 17.0 |first=Jen |last=Simmons |date=September 18, 2023 |website=WebKit}}</ref> Safari 18.4 added support for Opus and Vorbis codecs with Ogg containers when using macOS Sequoia 15.4 or iOS 18.4 and later.<ref name="safari-18-4-notes">{{cite web |title=Safari 18.4 Release Notes |url=https://developer.apple.com/documentation/safari-release-notes/safari-18_4-release-notes |website=Apple Developer Documentation |access-date=25 September 2025}}</ref><ref name="webkit-18-4-blog">{{cite web |last1=Simmons |first1=Jen |title=WebKit Features in Safari 18.4 |url=https://webkit.org/blog/16574/webkit-features-in-safari-18-4/ |website=WebKit |date=31 March 2025 }}</ref>

On Windows 10, version 1607, Microsoft provided native support for Opus audio encapsulated in Matroska and WebM containers.<ref>{{Cite web|url=https://blogs.windows.com/msedgedev/2016/04/18/webm-vp9-and-opus-support-in-microsoft-edge/|title=WebM, VP9 and Opus Support in Microsoft Edge|first=Microsoft Edge|last=Blog|date=April 18, 2016|website=Microsoft Edge Blog}}</ref> On version 1709, support for Opus audio encapsulated in Ogg containers was made available through a pre-installed add-on called Web Media Extensions.<ref>{{Cite web|url=https://www.ctrl.blog/entry/windows-ogg.html|title=Microsoft adds Ogg, Theora, and Vorbis media formats to Windows 10|first=Daniel|last=Aleksandersen|website=www.ctrl.blog|date=28 December 2021 }}</ref> On Windows 10 version 1903, native support for the <code>.opus</code> extension was added.<ref name=":0" /> On Windows 8.1 and older, third-party decoders, such as LAV Filters, are available to provide support for the format.<ref name="lavfilters">{{cite web |url=http://lavfilters.googlecode.com/ |archive-url=https://archive.today/20130103042554/http://lavfilters.googlecode.com/ |url-status=dead |archive-date=2013-01-03 |title=lavfilters — Open-Source DirectShow Media Splitter and Decoders |publisher=Google Project Hosting |access-date=2012-10-05}}</ref> A January 2024 update for Windows 10 & 11 caused File Explorer to freeze up when renaming or deleting Ogg files (including .oga, .ogg, .ogm, .ogv, .ogx, .opus), due to bugs involving the '''MF Media Source Pack Property Handler''' shell extension by Microsoft and the '''Web Media Extensions''' package in Windows, which were not patched before the Windows Updates were rolled out.<ref>{{Cite web|url=https://thegeekpage.com/ogg-files-are-crashing-file-explorer/|title=ogg files are crashing file explorer in Windows 10|date=8 May 2021 }}</ref>

iOS 17 includes support for natively encoding and decoding the Opus codec through the operating system's AudioToolbox framework. Playback of Ogg files in the <code>.opus</code> container is supported through the Files application. Opus is additionally supported within the Core Audio Format <code>.caf</code> container, the QuickTime <code>.mov</code> container, and the ISOBMFF or MP4 file format <code>.mp4</code> container.{{NoteTag|name=ios-m4a|Opus will only work standalone on iOS 17 in ISOBMFF/MP4 if its "major version", the container's "brand", or "ftype", is ''not'' "M4A ". iOS expects audio files to use the <code>.m4a</code> extension,<ref name="loc">{{cite tech report |publisher=Library of Congress |location=Washington, D.C. |series=Sustainability of Digital Formats |type=Full draft |title=MPEG-4 File Format, Version 2 |date=25 April 2023 |url=https://www.loc.gov/preservation/digital/formats/fdd/fdd000155.shtml#sign |access-date=2024-06-23 |website=www.loc.gov}}</ref> relegating <code>.mp4</code> to video, so playback will present a blank video track even if none are present within the container. Re-naming a <code>.mp4</code> file to <code>.m4a</code> will work as expected, however.}} As the AudioToolbox framework is shared with macOS, similar support should be present in both operating systems as they further develop.<ref>{{Cite web |title=Audio Toolbox |url=https://docs.developer.apple.com/documentation/audiotoolbox/ |access-date=2024-06-24 |website=Apple Developer Documentation |language=en-US}}</ref> In 2024, Apple Podcasts does not support Opus.<ref>{{Cite web |title=Audio requirements – Apple Podcasts for Creators |url=https://podcasters.apple.com/support/893-audio-requirements |access-date=2024-12-31 |website=podcasters.apple.com |language=en |quote=For RSS feeds, Apple Podcasts accepts MP3 or AAC formats}}</ref>

{| class="wikitable" style="width: 100%;" |+ Opus support by different operating systems |- ! scope="row" | ! Windows ! macOS ! Linux ! Android ! iOS |- ! scope="row" | Codec support | {{yes|Yes '''Partial''': Win 10 v1607, 1709, 1809 '''Full''': Win 10 v1903}} | {{yes|Yes '''Partial''': macOS High Sierra (10.13) '''Full''': macOS Sonoma (14.0)}} | {{yes}} | {{yes|Yes '''Partial''': Android 5, 6, 7 '''Full''': Android 10}} | {{yes|Yes '''Partial''': iOS 11 '''Full''': iOS 17}} |- ! scope="row" | Container support | '''On Windows 10 Anniversary Update (1607)''': WebM (.webm is not recognised; requires pseudo extension) Matroska (.mka, .mkv) '''On Windows 10 Fall Creators Update (1709) with Web Media Extensions add-on''': Ogg (.opus is not recognised; requires pseudo extension){{NoteTag|name=Supported-File-Ext|On Android 9 and Microsoft Windows 10 (1809), the <code>.opus</code> filename extension isn't recognized by Android's MediaScanner service and Universal Windows Platform apps. A pseudo extension of another audio format (such as <code>.ogg</code> or <code>.m4a</code>) is required to detect and playback files.<ref name="Android-Supported-File-Ext">{{cite web |url = https://source.android.com/compatibility/7.0/android-7.0-cdd#5_1_1_audio_codecs |title = Android 7.0 (N) Compatibility Definition |access-date=2017-05-22}}</ref><ref name="Windows-Supported-File-Ext">{{Cite web|url=https://learn.microsoft.com/en-us/previous-versions/windows/apps/hh986969(v=win.10)|title=Supported audio and video formats (Windows Runtime apps) – Windows app development|website=learn.microsoft.com|date=13 October 2015 }}</ref>}} '''On Windows 10 October 2018 Update (1809)''': WebM (.webm is recognised officially) '''On Windows 10 May 2019 Update (1903)''': Ogg (.opus, .oga, .ogg) (.opus is recognised officially) | '''On macOS High Sierra''': Core Audio Format (.caf) '''On macOS Monterey''': WebM (.webm; experimental support)<ref>{{Cite web|url=https://webkit.org/blog/11989/new-webkit-features-in-safari-15/|title=New WebKit Features in Safari 15|first=Jen|last=Simmons|date=October 26, 2021}}</ref><ref>{{Cite web|url=https://developer.apple.com/documentation/safari-release-notes/safari-15-release-notes|title=Apple Developer Documentation|website=developer.apple.com}}</ref>'''On macOS Sonoma''': mono and stereo MPEG-4 and WebM (.webm)<ref name="safari-17-notes" /><ref name="webkit-17-blog" />'''On macOS Sequoia''': Ogg container support in Safari 18.4 and later<ref name="safari-18-4-notes" /><ref name="webkit-18-4-blog" /> | Ogg (.opus) WebM (.webm) Matroska (.mka, .mkv) MPEG-TS (.ts) | '''On Android 5''': WebM (.webm) Matroska (.mka, .mkv) '''On Android 7''': Ogg (.oga, .ogg) (.opus is not recognised; requires pseudo extension){{NoteTag|name=Supported-File-Ext}} '''On Android 10''': Ogg (.opus, .oga, .ogg) (.opus is recognised officially) MP4 (.mp4) (together with AV1 video) | '''On iOS 17 and later''': Supports playback through Files; supports Ogg as .opus; supported in MP4, standalone{{NoteTag|name=ios-m4a}} or in combination with any officially supported video codec; standalone and expanded but unofficially supported combinations in MOV; standalone support in CAF'''On iOS 18.4 and later''': Ogg container support in Safari 18.4 and later<ref name="safari-18-4-notes" /><ref name="webkit-18-4-blog" /> |- ! scope="row" | Notes | '''On Windows 10 & Windows 11''': – As of June 2023, Windows Media Player (2022) does not support Opus audio tracks that accompany videos in MP4 containers.<ref>{{Cite web|url=https://superuser.com/questions/1741619/windows-11s-new-media-player-cannot-play-opus-encoded-audio-in-mp4-file|title=Windows 11's new media player cannot play opus encoded audio in mp4 file – Super User}}</ref> '''On Windows 10''': – On Anniversary Update (1607), limited support is available in Microsoft Edge (via MSE only) and Universal Windows Platform apps. Windows Media Player does not support Ogg; only WebM and Matroska. – On April 2018 Update (1803) with [https://www.microsoft.com/store/productId/9N5TDP8VCMHS Web Media Extensions] preinstalled, Microsoft Edge (EdgeHTML 17) supports Opus audio embedded in <audio> tags. – Up till October 2018 update (1809), the filename extension .opus was not recognised. (substitute with a pseudo file extension such as .m4a)<ref name="Windows-Supported-File-Ext" /> '''On Windows 8.1 and older''': – Requires installation of a third-party multimedia framework, LAV Filters. | In Safari 15, Apple added support for Opus audio in WebM containers. Experimental support is only present in macOS.<ref>{{Cite web|url=https://zenn.dev/futa/articles/8cf0f84eadc910400b02|title=Webに最適なメディアフォーマットを整理する – 2021|website=Zenn|date=8 November 2021 }}</ref> |{{n/a}} |– Up till Android 9, the filename extension .opus was not recognised (substitute with a pseudo file extension such as .ogg or .m4a)<ref name="Android-Supported-File-Ext" /> |– When originally introduced in iOS 11, only constant bitrate Opus audio in a CAF container was supported. {{dash}}In Safari 15, Apple added support for Opus audio in WebM containers. However, it is non-functional in iOS 15, as of September 2021.<ref>{{Cite news|url=https://9to5mac.com/2021/08/10/apple-adding-webm-audio-codec-support-to-safari-with-ios-15/|title=Apple adding WebM audio codec support to Safari with iOS 15|first=Filipe|last=Espósito|newspaper=9To5Mac |date=August 10, 2021}}</ref>– In iOS 17, native support for playing variable bitrate multichannel .opus files through Quick Look in the Files app was implemented; the codec is additionally natively supported if encapsulated in ISOBMFF/MP4, CAF, or MOV.– As of iOS 17, WebM support is present in Safari, but not Files.– Opus can additionally be utilized within MP4 in combination with any video codec supported by the device. |}

====Media player support==== While support in multimedia frameworks automatically enables Opus support in software which is built on top of such frameworks, several applications developers made additional efforts for supporting the Opus audio format in their software. Such support was added to AIMP,<ref name="aimp">{{cite web|url=http://www.aimp.ru/index.php?do=changelog&ver=320 |title=AIMP: Home Page |publisher=Aimp.ru |access-date=2012-10-05}}</ref> Amarok,<ref name="amarok">{{cite web |url=http://amarok.kde.org/en/releases/2.8 |title=Amarok 2.8 "Return To The Origin" released |work=Amarok |date=2013-08-16 |access-date=2014-05-28 |archive-date=2014-06-24 |archive-url=https://web.archive.org/web/20140624064712/http://amarok.kde.org/en/releases/2.8 |url-status=dead }}</ref> cmus, Music Player Daemon, foobar2000,<ref name="foobar2000">{{cite web |url=http://www.hydrogenaud.io/forums/?showtopic=96057 |title=foobar2000 v1.1.14 beta |publisher=Hydrogenaudio Forums |access-date=2012-10-05 }}</ref> Mpxplay, MusicBee,<ref name="musicbee">{{cite web |url=http://getmusicbee.com/forum/index.php?topic=7206.0 |title=MusicBee |publisher=MusicBee Forum |access-date=2013-08-17 }}</ref> SMplayer, VLC media player,<ref name="vlc">{{cite web |url=http://www.videolan.org/vlc/releases/2.0.4.html |title= VLC 2.0.4 Twoflower |publisher=VideoLAN |access-date=2012-10-19 }}</ref> Winamp<ref name="winamp">{{cite web |url=http://forums.winamp.com/showthread.php?t=347029 |title=Winamp |date=16 August 2012 |publisher=Winamp Forums |access-date=2013-01-04}}</ref> and XMPlay audio players; Icecast,<ref name="Icecast">{{cite web |url=http://lists.xiph.org/pipermail/icecast/2012-July/012237.html |title=Icecast 2.4 beta release |date=17 July 2012 |publisher=Lists.xiph.org |access-date=2012-09-12 |archive-date=2012-09-01 |archive-url=https://web.archive.org/web/20120901234057/http://lists.xiph.org/pipermail/icecast/2012-July/012237.html |url-status=dead }}</ref> Airtime (software)<ref name="AirtimeAddsOpusSupport">{{cite web|last=Airtime|first=Changelog|title= Airtime/changelog at 2.4.x|url=https://github.com/sourcefabric/Airtime/blob/2.4.x/changelog|publisher=Sourcefabric|access-date=1 July 2013}}</ref> audio streaming software; and Asunder audio CD ripper, CDBurnerXP CD burner, FFmpeg, Libav and MediaCoder media encoding tools. Streaming Icecast radio trials are live since September 2012 and January 2013.<ref name="RadioJackieOpusTrial">{{cite web|last=Radio Jackie|first=Listen Now|title=Opus Stream|url=http://www.radiojackie.com/listennowpage.asp|publisher=Radio Jackie|access-date=14 May 2013|archive-date=12 October 2013|archive-url=https://web.archive.org/web/20131012190440/http://radiojackie.com/listennowpage.asp|url-status=dead}}</ref><ref name="AbsRadioOpusTrial">{{cite web |last=Absolute Radio|first=Listen Labs|title=Opus Streaming Trial|url=http://www.absoluteradio.co.uk/listen/labs.html#opus |publisher=Absolute Radio|access-date=30 October 2012}}</ref> SteamOS uses Opus or Vorbis for streaming audio.<ref name=steamdb>{{cite web |title=Steam Beta Update: SteamVR and In-Home Streaming Beta|url=https://steamdb.info/blog/steam-beta-vr-and-inhome-streaming/ |website=SteamDB|access-date=9 December 2015}}</ref>

====Browser support==== Opus support is mandatory for WebRTC implementations.<ref name="webrtc">{{cite web |url = http://heise.de/-1656611 |title= Zwei Audio-Codecs für Echtzeit-Kommunikation im Browser |website =Heise.de |date= 31 July 2012 |access-date=2012-09-12 }}</ref> Opus is supported in Mozilla Firefox,<ref name="gecko">{{cite web |url=https://developer.mozilla.org/En/Media_formats_supported_by_the_audio_and_video_elements#Ogg_Opus |title=Media formats supported by the HTML audio and video elements |publisher=Developer.mozilla.org |date=2012-09-03 |access-date=2012-09-12 |archive-url=https://web.archive.org/web/20100627072016/https://developer.mozilla.org/En/Media_formats_supported_by_the_audio_and_video_elements#Ogg_Opus |archive-date=2010-06-27 |url-status=dead}}</ref> Chromium and Google Chrome,<ref name="chromium-issue104241">{{cite web |url=https://code.google.com/p/chromium/issues/detail?id=104241 |title=Issue 104241: Support OPUS in Ogg files for the audio tag and Audio object |work=Chromium bug tracker |access-date=2014-05-28}}</ref> Blink-based Opera,<ref name="opera">{{cite web |url=http://my.opera.com/community/forums/topic.dml?id=1491802 |title=Why no official mention of Opus support? |publisher=My.opera.com |date=2012-07-19 |access-date=2012-09-12}}</ref><ref name="cnet">{{cite web|last=Shankland |first=Stephen |url=http://news.cnet.com/8301-1023_3-57494622-93 |title=How corporate bickering hobbled better Web audio |publisher=CNET News |date=2012-08-17 |access-date=2012-09-12 }}</ref> as well as all browsers for Unix-like systems relying on GStreamer for multimedia formats support. Although Internet Explorer will not provide Opus playback natively, support for the format is built into the Edge browser, along with VP9, for full WebM support.<ref>{{cite web |url = https://dev.windows.com/en-us/microsoft-edge/platform/status/opusaudiocodec |title=Platform status |publisher=Microsoft |date=2016-04-19 }}</ref><ref name=MSE>{{cite web |url = https://blogs.windows.com/msedgedev/2016/04/18/webm-vp9-and-opus-support-in-microsoft-edge/ |title=WebM, VP9 and Opus Support in Microsoft Edge |publisher=Microsoft |date=2016-04-18}}</ref> Safari supports Opus as of iOS 11 and macOS High Sierra.<ref name="webkit_opus">{{cite news |title=Announcing WebRTC and Media Capture |url= https://webkit.org/blog/7726/announcing-webrtc-and-media-capture/ |access-date=20 June 2017 |website=webkit.org|date=7 June 2017 |quote =available on Safari on macOS High Sierra, iOS 11, (…) Safari supports modern audio codecs such as Opus}}</ref>

====VoIP support==== Due to its abilities, Opus gained early interest from voice over IP (VoIP) software vendors. Several SIP clients, including Acrobits Softphone, CSipSimple (via additional plug-in), Empathy (via GStreamer), Jitsi,<ref name="xmpp.org-jitsi">{{cite web |url = http://xmpp.org/2013/03/jitsi-2-0-now-released/ |title=Jitsi 2.0 Now Released! |first=Ludovic |last=Bocquet |work=XMPP Foundation |date=2013-03-07 |access-date=2014-05-28 |archive-url=https://web.archive.org/web/20140529085047/http://xmpp.org/2013/03/jitsi-2-0-now-released/ |archive-date=2014-05-29 |url-status=dead }}</ref> Tuenti,<ref>{{cite web |url = https://vimeo.com/109608566|title=Tuenti+WebRTC (Voip2day 2014)|date=2014-10-21}}</ref> Line2 (currently only on iOS),<ref name="Line2">{{cite web |url = http://www.line2.com/home/2012/10/a-new-line2-for-ios-experience-with-improved-sound-quality/ |title = A new Line2 for iOS experience with improved sound quality |publisher=Line2 |date=2012-10-18 |access-date=2013-03-15 |archive-url=https://web.archive.org/web/20130315131608/http://www.line2.com/home/2012/10/a-new-line2-for-ios-experience-with-improved-sound-quality/ |archive-date=2013-03-15 |url-status=dead }}</ref> Linphone,<ref name="Linphone">{{Cite web|url=https://www.linphone.org/technical-corner/linphone?qt-technical_corner=1#qt-technical_corner|title=Linphone | Linphone|website=www.linphone.org}}</ref> Phoner and PhonerLite,<ref name="Phoner">{{Cite web|url=http://phonerlite.de/config_en.htm|title=PhonerLite: configuration|website=phonerlite.de}}</ref> SFLphone,<ref name="SFLphone">{{cite web |url = https://projects.savoirfairelinux.com/issues/14602 |archive-url=https://archive.today/20121217173556/https://projects.savoirfairelinux.com/issues/14602 |url-status=dead |archive-date=2012-12-17 |title=SFLphone — Task #14602: [Codec] Implement opus |publisher=Savoir-faire Linux |date=2012-08-13 |access-date=2012-09-12}}</ref> Telephone, Mumble, Discord<ref name="What Features Does Discord Have"/> and TeamSpeak 3 voice chat software also support Opus.<ref name="mumble">{{cite web |url = http://blog.mumblevoice.com/?p=39 |title=Mumble 1.2.4 Has been released |author=Brandon |work=Mumblevoice Blog |date=2013-06-19 |access-date=2014-05-28 |archive-url = https://web.archive.org/web/20140628191519/http://blog.mumblevoice.com/?p=39 |archive-date=2014-06-28 |url-status=dead}}</ref><ref name="teamspeak">{{cite web|url=http://forum.teamspeak.com/showthread.php/84285-TeamSpeak-3-Client-3-0-10-released |title=TeamSpeak 3 Client 3.0.10 released |publisher=TeamSpeak Forums |access-date=2013-03-04}}</ref><ref name="teamspeak2">{{cite web|url=http://forum.teamspeak.com/showthread.php/84284-TeamSpeak-3-Server-Version-3-0-7-released |title=TeamSpeak 3 Server Version 3.0.7 released |publisher=TeamSpeak Forums |access-date=2013-03-04}}</ref> TrueConf supports Opus in its VoIP products.<ref name="TrueConf">{{cite press release |url=http://trueconf.ru/company/news-events/press-release/audiocodec-opus.html |language=ru |title=TrueConf сделал ставку на аудиокодек Opus |trans-title=TrueConf opted for Opus audio codec |location=Moscow, Russia |date=2012-09-19 |access-date=2014-05-28 |url-status=dead |archive-url = https://web.archive.org/web/20140529051338/http://trueconf.ru/company/news-events/press-release/audiocodec-opus.html |archive-date=2014-05-29 }}</ref> Asterisk lacked builtin Opus support for legal reasons,<ref name="asterix-patents">{{cite mailing list |url = http://lists.digium.com/pipermail/asterisk-dev/2013-May/060419.html |title=Opus and VP8 |first=Matthew |last=Jordan |mailing-list=asterisk-dev |date=2013-05-29 |access-date=2014-05-28}}</ref> but a third-party patch was available for download<ref name="asterisk-patch">{{cite web |url = https://github.com/meetecho/asterisk-opus |title=Asterisk Opus/VP8 patch |work=GitHub |access-date=2014-05-28}}</ref> and official support via a binary blob was added in September 2016.<ref name="Opus-for-Asterisk">{{cite web |url = http://blogs.digium.com/2016/09/30/opus-in-asterisk/ |title=Opus for Asterisk |work=Inside the Asterisk |date=2016-09-30 |access-date=2016-10-03 |archive-date=2016-10-03 |archive-url=https://web.archive.org/web/20161003135358/http://blogs.digium.com/2016/09/30/opus-in-asterisk/ |url-status=dead }}</ref> Tox P2P videoconferencing software uses Opus exclusively.<ref name="tox-opus">{{cite web |url= https://github.com/irungentoo/toxcore/blob/master/toxav/audio.h#L36 |title=Tox codec handling source code |work=GitHub |access-date=2015-12-09}}</ref> Classified-ads distributed messaging app sends raw opus frames inside TLS socket in its VoIP implementation.<ref name="classified-ads">{{cite web |url = http://katiska.org/classified_ads/doc-0.09/classAudioEncoder.html |title=Classified-ads audio encoder documentation |access-date=2016-05-25}}</ref>

Opus is widely used as the voice codec in WhatsApp,<ref name="Register">{{cite news |last=Leyden |first=John |title= WhatsApp laid bare: Info-sucking app's innards probed |url = https://www.theregister.co.uk/2015/10/27/whatsapp_forensic_analysis/ |access-date=19 October 2019 |work=The Register |date=27 October 2015 }}</ref><ref name="Hazra">{{cite book |last1=Hazra |first1=Sudip |last2=Mateti |first2=Prabhaker |chapter=Challenges in Android Forensics |editor-last1=Thampi |editor-first1=Sabu M. |editor-last2=Pérez |editor-first2=Gregorio Martínez |editor-last3=Westphall |editor-first3=Carlos Becker |editor-last4=Hu |editor-first4=Jiankun |editor-last5=Fan |editor-first5=Chun I. |editor-last6=Mármol |editor-first6=Félix Gómez |title=Security in Computing and Communications: 5th International Symposium, SSCC 2017 |date=September 13–16, 2017 |publisher=Springer |isbn=9789811068980 |pages=286–299 (290) |doi=10.1007/978-981-10-6898-0_24 |chapter-url = https://books.google.com/books?id=1u09DwAAQBAJ&pg=PA290 }}</ref><ref name="Srivastava">{{cite book |last1=Srivastava |first1=Saurabh Ranjan |last2=Dube |first2=Sachin |last3=Shrivastaya |first3=Gulshan |last4=Sharma |first4=Kavita |chapter=Smartphone Triggered Security Challenges: Issues, Case Studies and Prevention |editor-last1=Le |editor-first1=Dac-Nhuong |editor-last2=Kumar |editor-first2=Raghvendra |editor-last3=Mishra |editor-first3=Brojo Kishore |editor-last4=Chatterjee |editor-first4=Jyotir Moy |editor-last5=Khari |editor-first5=Manju |title=Cyber Security in Parallel and Distributed Computing: Concepts, Techniques, Applications and Case Studies |year=2019 |publisher=John Wiley & Sons |isbn=9781119488057 |pages=187–206 (200) |doi=10.1002/9781119488330.ch12 |s2cid=214034702 |chapter-url = https://books.google.com/books?id=FzGtDwAAQBAJ&pg=PA200 }}</ref> which has over 1.5{{nbsp}}billion users worldwide.<ref name="techcrunch">{{cite news |last=Constine|first=Josh |title = WhatsApp hits 1.5 billion monthly users. $19B? Not so bad. |url = https://techcrunch.com/2018/01/31/whatsapp-hits-1-5-billion-monthly-users-19b-not-so-bad/ |access-date=February 8, 2018|website=TechCrunch|date=January 31, 2018|archive-url=https://web.archive.org/web/20180209063953/https://techcrunch.com/2018/01/31/whatsapp-hits-1-5-billion-monthly-users-19b-not-so-bad/|archive-date=February 9, 2018|url-status=live}}</ref> WhatsApp uses Opus at 8{{ndash}}16 kHz sampling rates,<ref name="Register" /><ref name="Srivastava" /> with the Real-time Transport Protocol (RTP).<ref name="Hazra"/> The PlayStation 4 video game console also uses the CELT/Opus codec for its PlayStation Network system party chat.<ref name="playstation">{{cite web |url = https://doc.dl.playstation.net/doc/ps4-oss/ |title = Open Source Software used in PlayStation®4 |publisher = Sony Interactive Entertainment Inc. |access-date=2017-12-11 }}</ref> The Source Engine uses Opus for its voice chat system.<ref>{{Cite web |last=Li |first=Zhenyang |date=2021-03-30 |title=Reversing Steam Voice Codec |url=https://zhenyangli.me/posts/reversing-steam-voice-codec/ |access-date=2023-10-22 |website=zhenyangli.me |language=en}}</ref> It is also used in the Zoom videoconferencing app.<ref>{{cite web |title=Premium Audio – Integrated Audio Makes Your Meetings Easy |url=https://explore.zoom.us/docs/doc/Zoom-Premium-Audio.pdf |website=Zoom |access-date=23 October 2023}}</ref>

===Hardware=== Since version 3.13, Rockbox enables Opus playback on supported portable media players, including some products from the iPod series by Apple, devices made by iriver, Archos and Sandisk, and on Android devices using "Rockbox as an Application".<ref name="rockbox_v313">{{cite web |author = Rockbox Contributors |url = http://www.rockbox.org/wiki/ReleaseNotes313 |title = Release notes for Rockbox v.3.13 |publisher=Rockbox |date=2013-03-05 |access-date=2013-03-21 }}</ref><ref name="RaaA">{{cite web |url=http://www.rockbox.org/wiki/RockboxAsAnApplication2010 |title=RockboxAsAnApplication2010 < Main < Wiki |website = Rockbox.org |access-date=2012-10-05 }}</ref> All recent Grandstream IP phones support Opus audio both for encoding and decoding. OBihai OBi1062, OBi1032 and OBi1022 IP phones all support Opus. Recent BlueSound wireless speakers support Opus playback.<ref>{{cite web |title = PULSE FLEX |url = http://www.bluesound.com/en-ca/products/pulse-flex/?cl#spec |website=BlueSound |access-date=28 February 2017}}</ref> Devices running Hiby OS, like the Hiby R3, are capable of decoding Opus files natively.

Many broadcast IP codecs include Opus such as those manufactured by Comrex, GatesAir and Tieline.<ref name="tieline">{{cite web |url = http://www.radiomagonline.com/studio_audio/ip_audio/tieline_integrates_opus_report-it_1218/ |title = Tieline Integrates OPUS into Report-IT and IP codecs |publisher=Radio Magazine |date=2012-12-18 |access-date=2012-12-18 |archive-url= https://web.archive.org/web/20130509230931/http://radiomagonline.com/studio_audio/ip_audio/tieline_integrates_opus_report-it_1218/ |archive-date=2013-05-09 |url-status=dead }}</ref>

The Sony PlayStation 5 supports capturing 1080p and 2160p footage using VP9 video and Opus audio in a WebM container.<ref>{{Cite web|url=https://www.operationsports.com/mlb-the-show-20-video-looks-amazing-in-4k-hdr-60-fps-on-playstation-5-load-times-also-revealed//|title=MLB The Show 20 Gameplay Video – 4K HDR 60 FPS on PlayStation 5, Load Times Also Revealed|date=14 November 2020|access-date=2021-04-19}}</ref><ref>{{Cite web|url=https://www.playstation.com/en-us/support/hardware/play-video-music-discs-usb-drives/|title=How to play video and music from discs and USB drives PlayStation (US)|website=www.playstation.com}}</ref>

Android 13 supports Opus as a bluetooth headphone (A2DP) codec, motivated by its low latency, which is important for head-tracked spatial audio. Google's Pixel Buds Pro supports this A2DP codec.<ref>{{cite web |last1=Rahman |first1=Mishaal |title=A firmware update is rolling out to the Pixel Buds Pro enabling spatial audio with head tracking. As expected, this uses the Opus codec over BT A2DP to minimize latency. |url=https://twitter.com/MishaalRahman/status/1633193898725064706 |website=Twitter |language=en}}</ref>

== Patent claims == As an open standard, the algorithms are openly documented, and a reference implementation (including the source code) is published. Broadcom and the Xiph.Org Foundation own software patents on some of the CELT algorithms, and Skype Technologies/Microsoft own some on the SILK algorithms; each offers a royalty-free perpetual license for use with Opus, reserving only the right to make use of their patents to defend against infringement suits of third parties. Qualcomm, Huawei, France Telecom, and Ericsson have claimed that their patents may apply, which Xiph's legal counsel denies, and none have pursued any legal action.<ref name="OpusLicense">{{cite web |url=https://www.opus-codec.org/license/ |title=Opus Codec License |publisher=Xiph.org |access-date=2015-12-22}}</ref><ref name="osnews">{{cite web |url=http://www.osnews.com/story/26892/Nokia_s_VP8_patent_claims_we_ve_been_here_before |title=Nokia's VP8 patent claims: we've been here before |publisher=OSNews |date=2013-05-25 |access-date=2014-07-17}}</ref> The Opus license automatically and retroactively terminates for any entity that attempts to file a patent suit.

Vectis sells a package of patents pools which are claimed that apply to Opus codec.<ref>{{cite web |url=https://www.opuspool.com | title=Opus Patent Pool}}.</ref> Opus Patent Pool is managed by Vectis and contains a series of patents owned by Dolby, Fraunhofer and NTT. Vectis have engaged in dispute against Epson and ended with an agreement.<ref>{{cite web |url=https://ipfray.com/epson-settles-audio-codec-dispute-with-dolby-takes-vectis-ip-pool-license-opus-standard-not-truly-royalty-free-arcelik-trial-next-week |title=EPSON settles audio codec dispute with Dolby, takes Vectis IP pool license: |publisher=ipfray | date=2025-10-10}}</ref> Actual legal dispute from Vectis are against Acer.<ref>{{cite web |url=https://www.vectis.com/media/vectis-opus-patent-pool-licensor-enforces-against-acer-before-the-upc |title=Vectis Opus Patent Pool Licensor Enforces Against Acer Before the UPC |date=2025-12-10 }}</ref>

== See also == {{Portal|Free and open-source software}} * Comparison of audio coding formats * FLAC (/flæk/; Free Lossless Audio Codec) * Streaming media * xHE-AAC

== Notes ==

== References == === Citations === {{refs|refs = <ref name="XDA Opus 1.2">{{cite web | first = Steven | last = Zimmerman | url = https://www.xda-developers.com/opus-codec-high-quality-audio-32-kbps/ | title = Opus 1.2 Codec Arrives on Your Phone: High Quality Audio at 32 kbps | publisher = XDA Developers | date = 2017-07-07 | access-date = 2017-07-12 | archive-url = https://web.archive.org/web/20170713002825/https://www.xda-developers.com/opus-codec-high-quality-audio-32-kbps/ | archive-date = 2017-07-13 }}</ref> <ref name="ValinAES135">{{cite web |author1=Jean-Marc Valin |author2=Gregory Maxwell |author3=Timothy B. Terriberry |author4=Koen Vos |title=High-Quality, Low-Delay Music Coding in the Opus Codec |url = http://jmvalin.ca/papers/aes135_opus_celt.pdf |website=www.xiph.org |publisher=Xiph.Org Foundation |access-date=19 August 2014 |location = New York, NY |date=October 17–20, 2013 |quote= 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. |archive-url=https://web.archive.org/web/20180714000735/http://jmvalin.ca/papers/aes135_opus_celt.pdf |archive-date=14 July 2018 |url-status=live }}</ref> }}

=== Sources ===

{{refbegin}} * 50px This article contains quotations from the Opus Codec website, which is available under the [https://creativecommons.org/licenses/by/3.0/ Creative Commons Attribution 3.0 (CC BY 3.0)] license. {{refend}}

== External links == {{Commons|Opus Audio Codec}}

* {{Official website|https://opus-codec.org/}} * [https://wiki.hydrogenaud.io/index.php?title=Opus Opus on Hydrogenaudio Knowledgebase]

Category:Speech codecs Category:Free audio codecs Category:Lossy compression algorithms Category:Xiph.Org projects Category:Software using the BSD license Category:Open formats