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48-457: CELT was meant to bridge the gap between Vorbis and Speex for applications where both high quality audio and low delay are desired. It is suitable for both speech and music. It borrows ideas from the CELP algorithm, but avoids some of its limitations by operating in the frequency domain exclusively. The original stand-alone CELT has been merged into Opus . Therefore, CELT as stand-alone format

96-533: A range encoder . In connection with the PVQ, CELT uses a technique known as band folding, which delivers a similar effect to spectral band replication (SBR) by reusing coefficients of lower bands for higher ones, but has much less impact on the algorithmic delay and computational complexity than the SBR. This works against “birdie” artifacts by preserving more richness in the appropriate frequency bands. The decoder unpacks

144-414: A "Venue=" tag or files could have multiple genre definitions. Most applications also support common de facto standards such as disc number and ReplayGain information. aoTuV is a notable forks which adds support for encoding at lower bitrates. aoTuV's changes were intended to be merged into the reference encoder periodically, but that only happened once in libvorbis 1.1, due to future merges being

192-549: A "taks [ sic ] that requires uninterrupted time, something I [ Chris Montgomery ] don't have alot [ sic ] of." Knowledge of Vorbis' specifications is in the public domain . Concerning the specification itself, the Xiph.Org Foundation reserves the right to set the Vorbis specification and certify compliance. Its libraries are released under the revised 3-clause BSD license and its tools are released under

240-488: A Vorbis successor was done in 2005 at Xiph.org as part of the Ghost project (initially talked about as “Vorbis II”). This discussion together with Vorbis creator Christopher Montgomery led to Jean-Marc Valin′s interest in a particularly low-latency codec. Valin has worked on CELT since 2007. In December 2007, the first draft version of libcelt was published as version 0.0.1, initially named “Code-Excited Lapped Transform”. CELT

288-508: A constant K (i.e. whose L1-norm equals K ). In set-builder notation : where ‖ p → ‖ 1 {\displaystyle \left\|{\vec {p}}\right\|_{1}} denotes the L1-norm of p → {\displaystyle {\vec {p}}} . As it stands, the set S tesselates the surface of an N -dimensional pyramid. If desired, we may reshape it into

336-428: A court of law. Vorbis is supported by several large digital audio player manufacturers such as Samsung , SanDisk , Rio , Neuros Technology , Cowon , and iriver . Tremor , a version of the Vorbis decoder which uses fixed-point arithmetic (rather than floating point ), was made available to the public on September 2, 2002 (also under a BSD-style license ). Tremor, or platform-specific versions based on it,

384-401: A decoder to jump into a running stream. With transform codecs so-called pre-echo artifacts can get audible, because the quantisation error of sharp, energy-heavy sounds ( transients ) can spread over the entire DCT block and the transient doesn't mask them backward in time as well as forward. With CELT each block can be further divided to thwart such artifacts. First work on plans and drafts for

432-485: A more "accurate" approximation of the original unit vector v → {\displaystyle {\vec {v}}} at the cost of larger integer codewords that require more bits to transmit. Suppose we wish to quantize three-dimensional unit vectors using the parameter K =2. Our codebook becomes: (0.707 = 2 / 2 {\displaystyle {\sqrt {2}}/2} rounded to 3 decimal places.) Now, suppose we wish to transmit

480-462: A patent search that supports its claims, outside parties (notably engineers working on rival formats) have expressed doubt that Vorbis is free of patented technology. The Xiph.Org Foundation has not released an official statement on the patent status of Vorbis, pointing out that such a statement is technically impossible due to the number and scope of patents in existence and the questionable validity of many of them. Such issues can only be resolved by

528-485: A sphere by "projecting" the points onto the sphere, i.e. by normalizing them: where ‖ p → ‖ 2 {\displaystyle \left\|{\vec {p}}\right\|_{2}} denotes the L2-norm of p → {\displaystyle {\vec {p}}} . Increasing the parameter K results in more quantization points, and hence typically yields

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576-898: A steady rate. Apple's iPod does not natively support Vorbis but through the use of Rockbox , an open-source firmware project, is capable of decoding Vorbis files on certain models. Similar statements apply to other devices capable of running Rockbox, as well. The Xiph.Org Foundation wiki has an up-to-date list of Vorbis-supporting hardware, such as portables, PDAs, and microchips. Also see Internet radio device for an overview. Software supporting Vorbis exists for many platforms. The multi-platform open-source VLC media player and MPlayer can play Ogg Vorbis files, as can Winamp and foobar2000 . Windows Media Player does not natively support Vorbis; however, DirectShow filters exist to decode Vorbis in Windows Media Player and other Windows multimedia players that support DirectShow. Vorbis

624-492: Is also supported in the multi-platform audio editing software Audacity , in the multi-platform multimedia frameworks FFmpeg , GStreamer and Helix DNA . Vorbis is well-supported on the Linux platform in programs like XMMS , xine , Amarok . A list of Vorbis-supporting software can be found at the Xiph.Org Foundation wiki and Vorbis.com website. Users can test these programs using the list of Vorbis audio streams available on

672-415: Is broken into noise floor and residue components, and then quantized and entropy coded using a codebook -based vector quantization algorithm. The decompression algorithm reverses these stages. The noise-floor approach gives Vorbis its characteristic analog noise-like failure mode when the bitrate is too low to encode the audio without perceptible loss. The sound of compression artifacts at low bitrates

720-399: Is more suited to implementation on the limited facilities available in commercial portable players. A number of versions that make adjustments for specific platforms and include customized optimizations for given embedded microprocessors have been produced. Several hardware manufacturers have expressed intentions to produce Vorbis-compliant devices and new Vorbis devices seem to be appearing at

768-591: Is named after the character Exquisitor Vorbis in the Discworld novel Small Gods by Terry Pratchett . The Ogg format is named after ogging , jargon from the computer game Netrek . Vorbis faces competition from other audio formats, such as MP3. Though Vorbis is technically superior (addressing many of the limitations inherent to the MP3 design), MP3 has a far higher public profile. Because Vorbis does not have financial support from large organisations, support for

816-415: Is now abandoned and obsolete. Development is going on only for its hybridised form as a layer of Opus, integrated with SILK . This article covers the historic, stand-alone format; for the integrated form and its evolution since the integration into Opus see the article on Opus. CELT's central feature is low algorithmic delay. It allows for latencies of typically 3 to 9 ms but is configurable to below 2 ms at

864-402: Is published under a permissive open-source license (the 2-clause BSD ). Like Vorbis , CELT is a fullband (entire human hearing range ) general-purpose codec, i.e. not specialized for special types of audio signals and therefore different from its sibling project Speex . The format enables for transparent results at high bitrates, as well as very decent quality at lower bitrates. All in all,

912-432: Is robust to transmission errors. Loss of whole packets as well as bit errors can be masked with a steady degradation of audio quality ( packet loss concealment , PLC). CELT is a transform codec based on the modified discrete cosine transform (MDCT) and concepts from CELP (with a code book for excitation, but in the frequency domain). The initial PCM-coded signal is handled in relatively small, overlapping blocks for

960-478: Is similar to reverberations in a large space. Vorbis streams can be encapsulated in other media container formats besides Ogg. A commonly used alternative is Matroska . It is also used in WebM , a container format based on a subset of Matroska. Vorbis streams can also be encapsulated in an RTP payload format. Vorbis metadata , called Vorbis comments , supports metadata tags similar to those implemented in

1008-555: Is the first version of that program to drop MP3 support in favor of Ogg Vorbis. In October 2017, Microsoft released support for Ogg media container, and Theora and Vorbis media formats as an optional add-on to Windows 10 and Xbox One, available for free in the Microsoft Store . Pyramid vector quantization Pyramid vector quantization ( PVQ ) is a method used in audio and video codecs to quantize and transmit unit vectors , i.e. vectors whose magnitudes are known to

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1056-643: Is therefore often referred to as Ogg Vorbis . Vorbis is a continuation of audio compression development started in 1993 by Chris Montgomery . Intensive development began following a September 1998 letter from the Fraunhofer Society announcing plans to charge licensing fees for the MP3 audio format. The Vorbis project started as part of the Xiphophorus company's Ogg project (also known as OggSquish multimedia project). Chris Montgomery began work on

1104-673: Is used in the CELT audio codec (inherited into Opus ) and the Daala video codec. As a form of vector quantization , PVQ defines a codebook of M quantization points, each of which is assigned an integer codeword from 0 to M −1. The goal of the encoder is to find the codeword of the closest vector, which the decoder must decode back into a vector. The PVQ codebook consists of all N -dimensional points p → {\displaystyle {\vec {p}}} with integer-only coordinates whose absolute values sum to

1152-586: The GNU General Public License . The libraries were originally released under the GNU Lesser General Public Licence , but a BSD license was later chosen with the endorsement of Richard Stallman . The Xiph.Org Foundation states that Vorbis, like all its developments, is completely free from the licensing or patent issues raised by proprietary formats. Although the Xiph.Org Foundation states it has conducted

1200-506: The ID3 standard for MP3. The metadata is stored in a vector of byte strings of arbitrary length and size. The size of the vector and the size of each string in bytes is limited to 2  − 1 (about 4.3 billion , or any positive integer that can be expressed in 32 bits). This vector is stored in the second header packet that begins a Vorbis bitstream. The strings are assumed to be encoded as UTF-8 . Music tags are typically implemented as strings of

1248-728: The .m4b of Myst IV: Revelation . As originally recommended by HTML 5 , these web browsers natively support Vorbis audio (without a plug-in) using the <audio> element: Mozilla Firefox 3.5 (and later versions), Google Chrome (from version 3.0.182.2), SeaMonkey (from version 2.0). Opera 9.5 experimental video builds released in 2007 and 2008 have only <video> support and play back Vorbis audio included in Ogg video files. Opera 10.5 browser has support for Vorbis audio, WAVE PCM audio and Theora video. The game design software RPG Maker MV, released in October 2015,

1296-552: The French music site Qobuz offers its customers the possibility to download their purchased songs in Vorbis format, as does the American music site Bandcamp . Vorbis I is a forward-adaptive monolithic transform codec based on the modified discrete cosine transform (MDCT). Vorbis uses the modified discrete cosine transform for converting sound data from the time domain to the frequency domain . The resulting frequency-domain data

1344-473: The MDCT ( window function ) and transformed to frequency coefficients. Choosing an especially short block size on the one hand enables for a low latency, but also leads to poor frequency resolution that has to be compensated. For a further reduction of the algorithmic delay to the expense of a minor sacrifice in audio quality, the by nature 50% of overlap between the blocks is practically cut down to half by silencing

1392-561: The Python code below, K =5 (codebook size: 102) yields an error of only 0.097 units, and K =20 (codebook size: 1602) yields an error of only 0.042 units. The PVQ codebook can be searched in O ( K N ) {\displaystyle O(KN)} . Encoding and decoding can likewise be performed in O ( K N ) {\displaystyle O(KN)} using O ( K + N ) {\displaystyle O(K+N)} memory. The codebook size obeys

1440-443: The compression capabilities are said to be significantly superior to those of MP3 , and as another useful feature for realtime applications like telephony, CELT's audio quality at lower bitrates are even on par with HE-AAC v1, thanks to the band folding. In comparative double-blind listening tests it proved to be noticeably superior to HE-AACv1 at ~64 kbit/s. It has a comparably low computational complexity that resembles that of

1488-403: The decoder but whose directions are unknown. PVQ may also be used as part of a gain/shape quantization scheme, whereby the magnitude and direction of a vector are quantized separately from each other. PVQ was initially described in 1986 in the paper "A Pyramid Vector Quantizer" by Thomas R. Fischer. One caveat of PVQ is that it operates under the taxicab distance (L1-norm). Conversion to/from

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1536-410: The form "[TAG]=[VALUE]", for instance, "ARTIST=The John Smith Band". The tag names are case-insensitive, thus typing "ARTIST=The John Smith Band" would be the same as "artist=The John Smith Band". Like the current version of ID3, users and encoding software are free to use whichever tags are appropriate for the content. For example, an encoder could use localized tag labels, live music tracks might contain

1584-1061: The format is not as widespread, though programs such as Audacity can convert to more popular formats, and support in games has gradually improved. The Vorbis format has proven popular among supporters of free software . They argue that its higher fidelity and completely free nature, unencumbered by patents, make it a well-suited replacement for patented and restricted formats. Vorbis has different uses for consumer products. Many video games store in-game audio as Vorbis, including Amnesia: The Dark Descent , Grand Theft Auto: San Andreas , Halo: Combat Evolved , Minecraft , and World of Warcraft , among others. Popular software players support Vorbis playback either natively or through an external plugin . A number of websites, including Misplaced Pages , use it. Others include Jamendo and Mindawn , as well as several national radio stations like JazzRadio, Absolute Radio , NPR , Radio New Zealand and Deutschlandradio . The Spotify audio streaming service primarily uses Vorbis as well as AAC . Also,

1632-478: The format was tentatively frozen (“soft freeze”) – reserving the possibility of unexpectedly necessary last changes. Shortly after the advent of the CELT/ SILK hybrid codec Opus (formerly known as Harmony), the development of CELT as a separate project was halted, instead living on the basis of Opus, which aims to treat the lower part of the spectral range in the time domain with linear prediction (SILK) and

1680-740: The higher part in the frequency domain with the MDCT . The draft for Opus has been registered at the IETF since September 2010. The software library libcelt serves as the reference implementation for CELT, written in C and published as free software under Xiph's own 3-clause BSD-ish license. Despite the format not being finally frozen, it was being used in many VoIP applications such as Ekiga and FreeSWITCH , which switched to CELT upon entering soft-freeze in January 2009, as well as Mumble , TeamSpeak and other software. In April 2011, support for CELT

1728-523: The individual components from the range coded bitstream, multiplies the band energy to the band shape coefficients and transforms them back (via iMDCT) to PCM data. The individual blocks are rejoined using weighted overlap-add (WOLA). Many parameters are not explicitly coded, but instead reconstructed by using the same functions as the encoder. For the channel coupling CELT may use M/S stereo or intensity stereo . Blocks can be described independent from adjacent frames ( Intra-frame ); for example to enable

1776-447: The low-delay variant of AAC (AAC-LD) and stays significantly below the complexity of Vorbis. It enables for constant and variable bitrate. If the signal disappears into the noise floor in speech pauses and similar cases, the transmission can be limited to signal the output of comfort noise to the decoder. Most settings of the naturally streaming-enabled format can be changed on the fly without interrupting transmission. The format

1824-570: The more familiar Euclidean distance (L2-norm) is possible via vector projection , though results in a less uniform distribution of quantization points (the poles of the Euclidean n -sphere become denser than non-poles). No efficient algorithm for the ideal (i.e., uniform) vector quantization of the Euclidean n -sphere is known as of 2010. This non-uniformity can be reduced by applying deformation like coordinate-wise power before projection, reducing mean-squared quantization error by ~10%. PVQ

1872-466: The price of more bitrate to reach a similar audio quality. CELT supports mono and stereo audio and is applicable to both speech and music. It can use a sampling rate from 32 kHz to 48 kHz and above and an adaptive bitrate from 24 kbit/s to 128 kbit/s per channel and above. There are no known intellectual property issues pertaining to the CELT algorithm, and its reference implementation

1920-564: The project and was assisted by a growing number of other developers. They continued refining the source code until the Vorbis file format was frozen for 1.0 in May 2000. Originally licensed as LGPL , in 2001 the Vorbis license was changed to the BSD license to encourage adoption, with the endorsement of Richard Stallman . A stable version (1.0) of the reference software was released on July 19, 2002. Since February 2013, Xiph.Org has stated that

1968-430: The raw DCT coefficients (normalisation). The coefficients of the resulting residual signal (so-called “band shape”) are coded by Pyramid Vector Quantisation (PVQ, a spherical vector quantisation ). This encoding leads to code words of fixed (predictable) length, which in turn enables for robustness against bit errors and leaves no need for entropy encoding . Finally, all output of the encoder are coded to one bitstream by

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2016-483: The recurrence with V ( N , 0 ) = 1 {\displaystyle V(N,0)=1} for all N ≥ 0 {\displaystyle N\geq 0} and V ( 0 , K ) = 0 {\displaystyle V(0,K)=0} for all K ≠ 0 {\displaystyle K\neq 0} . A closed-form solution is given by where 2 F 1 {\displaystyle {}_{2}F_{1}}

2064-441: The same wiki. For more information about support in software media players there is a comparison of media players available. Some newer Ubisoft games use Vorbis files renamed with the filename extension .sb0. It can therefore be played using a compatible player, although sometimes one must force a different sampling rate to hear it correctly. A number of tools are available for extracting sound from archived files such as

2112-432: The signal during one eight at both ends of a block, respectively. The coefficients are grouped to resemble the critical bands of the human auditory system. The entire amount of energy of each group is analysed and the values quantised for data reduction and compressed through prediction by only transmitting the difference to the predicted values ( delta encoding ). The (unquantised) band energy values are removed from

2160-413: The unit vector <0.592, −0.720, 0.362> (rounded here to 3 decimal places, for clarity). According to our codebook, the closest point we can pick is codeword 13 (<0.707, −0.707, 0.000>), located approximately 0.381 units away from our original point. Increasing the parameter K results in a larger codebook, which typically increases the reconstruction accuracy. For example, based on

2208-506: The use of Vorbis should be deprecated in favor of the Opus codec, which is also a Xiph.Org Foundation project and also free and open-source. Compared to Vorbis, Opus can simultaneously achieve higher compression efficiency—per both Xiph.Org itself and third-party listening tests —and lower encode/decode latency (in most cases, low enough for real-time applications such as internet telephony or live singing, rarely possible with Vorbis). Vorbis

2256-549: Was established as an IETF technology in July 2009 under the "ietfcodec" working group. In May 2009, a draft of RTP payload format for the CELT Codec was published. In version 0.9, the pitch prediction operating in the frequency domain used until then was replaced by a less complex solution with a pre- and postfilter pair in time domain, which was contributed by Raymond Chen of Broadcom . With CELT 0.11 from February 4, 2011

2304-553: Was included in FFmpeg . CELT is also supported or used by: Vorbis Vorbis is a free and open-source software project headed by the Xiph.Org Foundation . The project produces an audio coding format and software reference encoder/decoder ( codec ) for lossy audio compression , libvorbis . Vorbis is most commonly used in conjunction with the Ogg container format and it

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