Opus

2012-12-14T17:30:44Z

84.209.84.211:

{{Software Infobox
| name = Opus
| logo = [[Image:opus-logo.png|250px|Official Opus logo]]
| screenshot =
| caption = Opus Interactive Audio Codec
| maintainer = [http://xiph.org/ Xiph.Org Foundation]
| stable_release = 1.0.2
| preview_release = exp_analysis7
| operating_system = Windows, Mac OS/X, Linux/BSD
| use = Encoder/Decoder
| license = 3-clause BSD license
| website = [http://www.opus-codec.org/ opus-codec.org]
}}{{stub}}

'''Opus''' is a lossy audio compression format developed by the Internet Engineering Task Force (IETF) and made especially suitable for interactive real-time applications over the Internet<ref name=homepage />. As an open format standardised through Request for Comments (RFC) 6716, a reference implementation is provided under the 3-clause BSD license<ref name=homepage />. Many Software patents which cover Opus are licensed under royalty-free terms<ref name=FAQ />.

Opus incorporates technology from two codecs, the speech-oriented SILK codec and the low-latency CELT codec<ref name=RFC />. Opus can 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<ref name=RFC />. 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. 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<ref name=RFC />.

==Caracteristics==

==Notes and references==
# ''Opus Codec''. Opus (Home page). Xiph.org Foundation. Retrieved September 21, 2012. <ref name="homepage">{{cite web |url=http://opus-codec.org/ |title=Opus Codec |work=Opus |publisher=Xiph.org Foundation |type=Home page |accessdate=September 21, 2012}}</ref>
# ''Opus FAQ''. Opus (FAQ). Xiph.org Foundation. Retrieved September 21, 2012. <ref name="FAQ">{{cite web |url=hhttps://wiki.xiph.org/OpusFAQ |title=Opus FAQ |work=Opus |publisher=Xiph.org Foundation |type=Home page |accessdate=September 21, 2012}}</ref>
# ''RFC6716''. Mozilla Corporation, Skype Technologies S. A. Retrieved September 21, 2012.<ref name="RFC">{{cite web |url=http://tools.ietf.org/html/rfc6716 |title=RFC6716 |work=Opus |publisher=Mozilla Corporation, Skype Technologies S. A. |type=Home page |accessdate=September 21, 2012}}</ref>

Lossy

2012-12-12T09:31:25Z

84.209.84.211: /* List of common lossy formats */

'''Lossy''' compression is a form of compression that significantly reduce multimedia file size by throwing away information imperceptible to humans.

Human audio perception is not perfect. Lossy compression takes advantage of this characteristic. By selective discarding, much unnecessary information is thrown away. The amount of information discarded is usually adjustable, giving a compromise between smaller size with less quality and larger size with higher quality.

The downside to this is that waveform reconstructed from compressed information will never exactly match the original waveform.

== Does Lossy Encoding Preserve Surround Information? ==
Depending on the encoder and settings, degradation of surround imaging may happen. Use higher [[bitrate]] to prevent this from happening. Mid/Side stereo of [[LAME]] or [[Advanced Audio Coding|AAC]] does not destroy surround information. Also [[Musepack|MPC]] preserves surround information with standard settings reasonably well. The lower the [[bitrate]], the worse you can expect the surround imaging become.

* [http://www.hydrogenaudio.org/forums/index.php?act=ST&f=15&t=4639 More discussion]

== List of common lossy formats ==
* [[Advanced Audio Coding]] (AAC, also improperly known as [[MP4]] or [[M4A]])
* [[AC3]]
* [[ATRAC3]]
* [[DTS]]
* [[MP2]]
* [[MP3]]
* [[Musepack]] (also known as MPC, formerly known as MPEGplus or MP+)
* [[Opus]]
* (Ogg) [[Vorbis]]
* [[QDesign]]
* [[Speex]] (speech only)
* [[VQF]]
* [[Windows Media Audio]] (WMA)

== See Also ==
* [[Choosing the best codec]]
* [[Lossless]]

[[Category:Codecs]]

Hydrogenaudio Knowledgebase - User contributions [en]

Opus

Lossy