Audio - Vorbis

Vorbis is an 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 . This is often shortened to simply ogg because it is shorter to write/say and because Vorbis is the most common media format found in the Ogg container.

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 "Monty" 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 latest official version is 1.1.2 released on 2005 - 11-28 , but there are some fine-tuned forks available, like aoTuV beta 4.51. Source code (called libvorbis ) for the Xiph release is available from the official Vorbis.com web site , while many Windows binaries can be downloaded at Rarewares.org . Source code and binaries for the aoTuV release are available at the author's own site .

Popularity growth

The Ogg Vorbis format has proved popular among open source communities. They argue that its higher fidelity and completely free nature make it a natural replacement for the entrenched MP3 format. However, MP3 has been widely used since the mid- 1990s and, as of 2006 , is still the most prevalent lossy audio format.

In the commercial sector, Vorbis is being used in many newer video game titles (see list below). While currently somewhat patchy, the increasing number of hardware players that support Vorbis is encouraging (see the compatible hardware list below).

Many popular software players support the Vorbis format, with a few needing an external plugin (see the compatible software below). Another indication of Ogg Vorbis's increasing popularity is the number of music websites using it, such as Jamendo or Mindawn , as well as several national radio stations such as Radio France , CBC Radio and Virgin Radio providing additional Vorbis streams .

Codec comparisons

Many other lossy audio codecs exist, including:

Some listening -based, some more technical tests have attempted to find the best quality lossy audio codecs at certain bitrates. The tests linked here appear to show that: at 128 kbit/s , Ogg Vorbis and MPC performed better than other codecs. At 64 kbit/s, HE-AAC and mp3PRO performed better than other codecs. At higher bitrates (more than 128 kbit/s), most people do not hear significant differences. Many of these tests, however, are difficult to keep up-to-date due to the ever-changing versions of the codecs.

Vorbis is considered to be one of the highest quality audio codecs in use today. For many applications, Vorbis has clear advantages over other modern codecs, in that it is patent-free, and therefore free to use, implement, or modify as one sees fit, yet produces smaller files than most other codecs at equivalent quality.

Technical details

Ogg quality levels Quality Bitrate
-q-2 (only aoTuV beta3 and later) ~32 kbit/s
-q-1 ~45 kbit/s (original vorbis) ~48 kbit/s (aoTuV beta3 and later)
-q0 ~64 kbit/s
-q1 ~80 kbit/s
-q2 ~96 kbit/s
-q3 ~112 kbit/s
-q4 ~128 kbit/s
-q5 ~160 kbit/s
-q6 ~192 kbit/s
-q7 ~224 kbit/s
-q8 ~256 kbit/s
-q9 ~320 kbit/s
-q10 ~500 kbit/s

Given 44.1 kHz (standard CD audio sampling frequency ) stereo input, the encoder will produce output from roughly 45 to 500 kbit/s (32 to 500 kbit/s for aoTuV tunings) depending on the specified quality setting. Quality settings run from -1 to 10 (-2 to 10 for aoTuV tunings) and are an arbitrary metric; files encoded at -q5, for example, should have the same quality of sound in all versions of the encoder, but newer versions should be able to achieve that quality with a lower bitrate. The bitrates mentioned above are only approximate; Vorbis is inherently variable-bitrate (VBR), so bitrate may vary considerably from sample to sample.

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. 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), which many people find more pleasing to the ears than the metallic warbling in the MP3 format.

Many users feel that Vorbis reaches transparency (sound quality that is indistinguishable from the original source recording) at a quality setting of -q5, approximately 160 kbit/s. For comparison, it is commonly felt that MP3 reaches transparency at around 192 kbit/s (except for the frequency range, which only occasionally exceeds 16kHz), resulting in larger file sizes for the same sound quality.

Various tuned versions of the encoder (Garf, aoTuV or MegaMix) attempt to provide better sound at a specified quality setting, usually by dealing with certain problematic waveforms by temporarily increasing the bitrate. The most consistently cited problem with Vorbis is pre-echo , a faint copy of a sharp attack that occurs just before the actual sound (the sound of castanets is commonly cited as causing this effect). Most of the tuned versions of Vorbis attempt to fix this problem and to increase the sound quality of lower quality settings (-q0 through -q4). Some tuning suggestions created by the Vorbis user community (especially the aoTuV tunings) have been incorporated into the 1.1.0 release.

The Vorbis format supports bitrate peeling for reducing the bitrate of already encoded files, and an experimental implemention of this can be found here . At the moment, re-encoding files at a lower bitrate will preserve more quality than the bitrate peeler.

Vorbis streams can be encapsulated in other media container formats aside Ogg. Another choice is MKV .

Licensing

Knowledge of Vorbis's specifications is in the public domain . Concerning the specification itself, Xiph.org reserves the right to set the Vorbis specification and certify compliance. 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 says it has conducted 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 [1] . Xiph says that it was privately issued a legal opinion subject to attorney/client privilege . It 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 cannot be resolved outside of a court of law. Some Vorbis proponents have derided the uncertainty concerning the patent status as " FUD ": misinformation spread by large companies with a vested interest.

Ogg Vorbis is supported by several large digital audio player manufacturers such as Samsung , Rio , Neuros , Cowon and iRiver . Many feel that the growing support for the Vorbis codec within the industry supports their interpretation of its patent status, as multinational corporations are unlikely to distribute software with questionable legal status. The same could be said about its growing popularity in other commercial enterprises like mainstream computer games.

Use in video games

Since the Vorbis libraries are available under a BSD licence (a free software approved licence) and the format itself is accepted as not covered by patents, several video game developers [2] have chosen to use Vorbis in their games rather than pay for patent-encumbered competitors like MP3. Some PC examples include:

A full list can be found at Xiph.org Wiki

In addition to the PC, Vorbis has also gained popularity on video game consoles due to the need for developers to compress game data. Known console games which use Vorbis include:

Hardware and software support

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 that make adjustments for specific platforms and include customized optimizations 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.

Hardware

The VorbisHardware node at the xiph.org wiki has an up-to-date list of Vorbis-supporting hardware, such as portables, PDAs, and microchips.

Software

The VorbisSoftwarePlayers node at the xiph.org wiki has an up-to-date list of Vorbis-supporting software for all operating systems. Users can test these players using the list of Vorbis audio streams available at [3] .

Although Apple iTunes does not natively read Vorbis, Xiph.org provides a QuickTime component [4] which can be used in iTunes.

Windows DirectShow filters [5] exist to decode Vorbis in multimedia players like Windows Media Player .

In July 2002 , RealNetworks announced that they would support Ogg Vorbis in their products. See Helix project for more details.

Trivia

See also

Listening tests

External links

 

MediaCoder - The universal audio/video batch transcoder
 MediaCoder is a free software written by Stanley Huang.
Feel free to play with it and distribute it.

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