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I noticed this codec when I was reading the Firefox 15 release notes. It also seems to be coming in VLC 2.0.4:




  • 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 full-band
  • 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




Opus is an open and royalty-free lossy audio compression format developed by the IETF and made especially suitable for interactive real-time applications over the Internet.[4] Opus incorporates technology from the speech-oriented SILK codec and the low-latency CELT codec.[4]

Opus can seamlessly scale to high and low bitrates and can transition between a linear prediction codec at lower bitrates and a transform codec at higher bitrates, as well as a hybrid for a short overlap. Opus has very low algorithmic delay compared to popular music formats such as MP3, Vorbis, and HE-AAC, and yet performs very competitively with them in terms of quality per bitrate.[5] Also unlike these codecs, Opus does not require the definition of large codebooks for each individual file, making it also preferable for short clips of audio.[6]

The bitstream has been frozen since January 8, 2012,[7] and a reference implementation is provided under the 3-clause BSD license.


In July, a prototype of a hybrid format was presented that combined the two proposed codec candidates SILK and CELT. In September 2010, Opus was submitted to the IETF as proposal for standardization. In October 2010, the format got its present name.[14] The bitstream format is tentatively frozen since beginning of February 2011 subject to last changes.[15] Near the end of July 2011, Jean-Marc Valin got a paid job at Mozilla Corporation to continue working on Opus.[16] In November 2011, the working group issued the last call for changes on the bitstream format. On July 2 2012, Opus was approved by the IETF for standardization.[17] An approximate date of late August 2012 was given for the official release of the final specification and of version 1.0 of the reference software.[17]


Opus has been shown to have excellent quality,[5] and at higher bit rates, it turns out to be competitive with codecs with much higher delay, such as HE-AAC and Vorbis.[18]

In listening tests the codec shows superior quality compared to HE-AAC codecs, which have so far been dominant in that area because of their use of the proprietary spectral band replication (SBR) technology.[19][20]


Firefox 15 Release Notes

Firefox - Opus Support for WebRTC

VLC - Ticket #7185 - Add support for decoding new audio format: Opus

VideoLAN Dev Days '12

Edited by jaxa
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Sounds pretty cool. I mainly use Vorbis myself because I feel it sounds better than mp3 and I've been burned by proprietary formats in the past. I'm kind of surprised they only go to 48 KHz though for Opus. With the push for HD material and many people having high-bandwidth connecctions, I would imagine some folks would want 96 KHz, or possibly even higher in the future.


I was wondering the other day if someone has ever tried to design a codec based around OpenCL/CUDA? Basically, music has parts that repeat over and over again, so you take the input file, shatter it into an insane amount of fragments (one fragment = x samples). Then you use a massively parallel system to find samples that are the same by comparing them all to eachother. Then you generate a substitution table which would tell the decoder where to swap fragments around, throw out the repetative batches of samples and reassemble the file, packing in the substitution table. Back when mp3/ogg/flac/etc were designed, they did not have hardware remotely capable of doing this in a reasonable time.


You could do this and then also use traditional audio compression methods to make files even smaller.

Edited by lost_soul

--- War does not decide who is right, war decides who is left.

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Also, I was wondering if it is possible to hide a secret message in a music file. A wile ago, it came out that your e-mail address is kept inside music files purchased from Itunes. This can be viewed with a hex editor if you do not believe me. My question is, could they store the information *in the music* and have it stay intact even if you transcode it? Imagine this. There's 44.1 KHz per second. Now if you take 2 samples per second and use them to represent bits throughout the song, you could embed a message that I doubt the human could notice. You would use quiet samples at a designated low-frequency tone to avoid disturbing the human.

--- War does not decide who is right, war decides who is left.

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"It's official. The Opus audio codec is now standardized by the IETF as RFC 6716. Opus is the first state-of-the-art, fully Free and Open audio codec ratified by a major standards organization. Better, Opus covers basically the entire audio-coding application space and manages to be as good or better than existing proprietary codecs over this whole space. Opus is the result of a collaboration between Xiph.Org, Mozilla, Microsoft (yes!), Broadcom, Octasic, and Google. See the Mozilla announcement and the Xiph.Org press release for more details."
Edited by jaxa
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