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Vorbis is a completely open and free audio compression (codec) project from the Xiph.org Foundation. It is frequently used in conjunction with the Ogg container and is then called Ogg Vorbis.
Vorbis was started following a September 1998 letter from Fraunhofer Gesellschaft announcing plans to charge licensing fees for the MP3 format. Soon after founder Christopher Montgomery began work on the project, he was assisted by a growing collection of other developers. They continued refining the code until a stable version 1.0 of the codec was released on July 19, 2002.
The Ogg Vorbis format has proved popular among open source communities; they argue that due to its higher fidelity and completely free nature, it is a natural replacement for the entrenched MP3 format. However, MP3 has a popular history dating back to the mid-1990s and as of 2004 is still the primary lossy audio format. It may be some time before one sees more Ogg format files than MP3 files. In the commercial sector, Vorbis has already had success with many newer video game titles employing Vorbis as opposed to MP3. An increasing number of hardware players is encouraging its growth as of July 2004; see the compatible hardware below.
Given 44.1 kHz (standard CD audio sample frequency) stereo input, the current encoder as of July 2004 will produce output from 45 to 500 kbit/s depending on the specified quality setting. Though Vorbis 1.0.1 is tuned for bitrates of 16 to 128 kbit/s/channel it is still possible to encode arbitrary bitrates chosen by the user. Such figures are only approximate, however, as Vorbis is inherently variable-bitrate (VBR).
Vorbis uses the modified discrete cosine transform (MDCT) for converting sound data from the time domain to the frequency domain. The resulting frequency-domain data 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.
Vorbis's specifications are in the public domain, its libraries are released under a BSD-style license, and its tools are released under the GPL (GNU General Public License).
The Xiph.org Foundation says that Vorbis, like all its developments, is completely free from the licensing or patent issues raised by other proprietary formats such as MP3. Although Xiph claims to have conducted a limited patent search that supports its claims, outside parties have expressed doubt that Vorbis is free of patented technology. Xiph says that it was issued a legal opinion privately subject to attorney/client privilege, and has not released an official statement on the patent status of Vorbis. No conclusive evidence has been presented that Vorbis is or is not patent-free as of 2004. Some Vorbis proponents have derided the uncertainty concerning the patent status as "FUD" disinformation spread by large companies with a vested interest.
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, is more suited to implementation on the limited facilities available in commercial audio systems (such as portable players). A number of versions, which make adjustments for specific platforms, and which include customised optimisations for given embedded microprocessors, have been produced. Several hardware manufacturers have expressed an intention to produce Vorbis-compliant devices, and new Vorbis devices seem to be appearing at a steady rate, especially in South Korea, although availability might differ from country to country.
The has an up-to-date list of Vorbis-supporting hardware, such as portables, PDAs, and microchips.
Here are a few examples of devices that play Ogg Vorbis files:
In July 2002, RealNetworks announced that they will support Ogg Vorbis in their products. See Helix project for more details.
"Ogg" is not named after the witch Nanny Ogg in Terry Pratchett's Discworld books. However, "Vorbis" is named after another Discworld character, High Priest Vorbis in Small Gods.
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