Encyclopedia
Vorbis is an
open source,
lossy audio codec project headed by the
Xiph.org Foundation. It is most commonly used in conjunction with the
Ogg container and is then called
Ogg Vorbis. Although the Vorbis format is often simply referred to as
Ogg, this is technically incorrect as Ogg, like AVI or
Matroska, is a container format while Vorbis is an audio codec. This can be mildly confusing, but even the codec's creator has been known to call Vorbis files "oggs."
Vorbis development began following a September 1998 letter from Fraunhofer Gesellschaft announcing plans to charge licensing fees for the
MP3 format. Soon after, founder Christopher "Monty" Montgomery, commenced work on the project and was assisted by a growing number of other developers. They continued refining the
source 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 such as aoTuV. Source code for the Xiph.org release is available from the official .
Usage
The Ogg Vorbis format has proven popular among supporters of open source. They argue that its higher fidelity and completely free nature make it an excellent replacement for patented and restricted formats like
MP3. However, MP3 has been widely used since the mid-
1990s and
as of 2006, is still the most popular standard in the consumer electronics industry. Of the consumer products supporting lossy compressed digital audio, virtually all support playback of MP3 audio while relatively few support alternative formats like Ogg Vorbis.
In the commercial sector, Vorbis support is on the rise. Many mainstream
video game titles store game audio as Vorbis and it is supported on many consumer electronics like digital audio players. Popular software players support Ogg Vorbis playback either natively or through an external plugin. A number of websites use it such as
Jamendo and Mindawn, as well as several national radio stations like
Radio France, CBC Radio and
Virgin Radio. Since it is not encumbered by patents and has been found to offer high audio fidelity, Vorbis is the preferred audio format on
Wikipedia and many other
wikis.
Codec comparisons
For many applications, Vorbis has clear advantages over other lossy audio codecs in that it is patent-free and has open-source implementations and therefore is free to use, implement, or modify as one sees fit, yet produces smaller files than most other codecs at equivalent or higher quality.
Listening tests have attempted to find the best quality lossy audio codecs at certain bitrates. Some conclusions made by recent listening tests:
- At 128kb/s the shows a four-way tie between aoTuV Vorbis, LAME-encoded MP3, WMA Pro, and QuickTime AAC, with each codec essentially transparent .
- At mid to low bitrates, private tests shows that aoTuV Vorbis has a better quality than other lossy audio codecs .
- At high bitrates , most people do not hear significant differences. However, trained listeners can often hear significant differences between codecs at identical bitrates, and aoTuV Vorbis performs very well, i.e. better than other formats such as AAC, MP3, and MPC .
Many of these results, however, are difficult to keep up to date due to the ever-evolving nature of the codecs.
Listening tests
Listening tests are normally carried out as ABX tests, i.e., the listener has to identify an unknown sample X as being A or B, with A and B available for reference. The outcome of a test must be statistically significant. This setup ensures that the listener is not biased by his/her expectations, and that the outcome is not likely to be the result of chance. If sample X can be identified reliably, the listener can assign a score as a subjective judgement of the quality. Otherwise, the encoded version is considered to be
transparent. Below are links to several listening test results.
- . Results suggest that further group testing at this bitrate is unnecessary because all codecs are statistically tied near transparency.
- . States that aoTuV beta 4 is the best encoder for either classical or various music in this bitrate, and that its quality is comparable to the LAME ABR MP3 at 128 kbit/s.
. States that aoTuV beta 4 and AAC are tied as the best encoders for classical music in this bitrate, while aoTuV beta 4 is the best encoder for pop music, even better than LAME at 128 kbit/s.
- . An audiophile listening test, which states that, for classical music, aoTuV beta 4 has 93% percent probability of being the best encoder, tied with MPC. MPC is tied with both Vorbis, in the first place, and LAME in the second.
-
Technical details
Vorbis nominal bitrate at quality levels for 44.1 kHz stereo input
| Quality | Nominal Bitrate |
|---|
| Official Xiph.org Vorbis | aoTuV beta 3 and later |
|---|
| -q-2 | not available | 32 kb/s |
| -q-1 | 45 kb/s | 48 kb/s |
| -q0 | 64 kb/s | |
| -q1 | 80 kb/s | |
| -q2 | 96 kb/s | |
| -q3 | 112 kb/s | |
| -q4 | 128 kb/s | |
| -q5 | 160 kb/s | |
| -q6 | 192 kb/s | |
| -q7 | 224 kb/s | |
| -q8 | 256 kb/s | |
| -q9 | 320 kb/s | |
| -q10 | 500 kb/s | |
Given 44.1 kHz stereo input, the encoder will produce output from roughly 45 to 500 kbit/s depending on the specified quality setting. Quality settings run from -1 to 10 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 , so bitrate may vary considerably from sample to sample.
Vorbis uses the modified discrete cosine transform 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 , which many people find more pleasant than the metallic warbling in the MP3 format.
Many users feel that Vorbis reaches
transparency 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, resulting in larger file sizes for the same sound quality.
Various
tuned versions of the encoder 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 . Most of the tuned versions of Vorbis attempt to fix this problem and to increase the sound quality of lower quality settings . Some tuning suggestions created by the 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 is available. However, encoding at the lower bitrate will result in better audio quality than this experimental bitrate peeler.
Vorbis streams can be encapsulated in other media container formats besides Ogg. A commonly used alternative is Matroska.
Metadata
Vorbis metadata, called comments, support metadata 'tags' similar to those implemented in the ID3 standard for MP3. The metadata is stored in a vector of eight-bit-clean strings of arbitrary length and size. The size of the vector and the size of each string in bytes is limited to 2
32-1 . 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 the form "[TAG]=[VALUE]", for instance, "ARTIST=The John Smith Band". Since there is no strict field definition as in 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 a "Venue=" tag or files could have multiple genre definitions. Most applications also support common de facto standards such as discnumber and Replay Gain information.
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 . The libraries were originally released under the
GNU Lesser General Public Licence, but a BSD licence 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 other proprietary formats such as
MP3. Although Xiph.org says it has conducted a patent search that supports its claims, outside parties have expressed doubt that Vorbis is free of patented technology .
Xiph.org maintains 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 Technology,
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.
Hardware and software support
Hardware
Tremor, a version of the Vorbis decoder which uses fixed-point arithmetic , was made available to the public on September 2, 2002 . Tremor, or platform specific versions based on it, 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 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 may differ from country to country.
The has an up-to-date list of Vorbis-supporting hardware, such as portables, PDAs, and microchips. Most digital audio players supported by
Rockbox, an open-source firmware project, are capable of decoding Vorbis.
Software
Software supporting Vorbis exists for many platforms. Although
Apple iTunes does not natively support Vorbis, Xiph.org which can be used in iTunes and QuickTime on both
Microsoft Windows and
Mac OS. On Windows, exist to decode Vorbis in multimedia players like
Windows Media Player and others which support
DirectShow. Vorbis is well-supported on the
Linux platform in programs like
XMMS,
xine, and many more.
More information about Vorbis-supporting software can be found at the . Users can test these programs using the list of Vorbis audio streams available at .
Trivia
- "Ogg" is derived from ogging, jargon that arose in the computer game, Netrek. Originally meaning a kamikaze attack and later, more generally, to do something forcefully possibly without consideration of the drain on future resources.
- "Vorbis" is named after a Discworld is a series [i] of thirty-four fantasy novels, a number of short stories, and ...
character, High Priest Vorbis in Small Gods is a novel [i] by Terry Pratchett [i], the thirteenth part of the popular Discworld [i] ...
.
See also
and playing sound files on Wikipedia
- Ogg bitstream format
- Vorbis comment, metadata format used by Vorbis
- XSPF, playlist format
- Comparison of audio codecs
- Xiph QuickTime Components, official QuickTime implementation
- FreeCast, peer-to-peer Vorbis streaming
External links
-
- - Xiph reference implementation
- Other encoder / decoder implementation:
-
-
-
- - aoTuV Vorbis tuned implementation
- - Optimized versions of aoTuV Vorbis encoder and other SSE/MultiThread optmizations
-
- Software / hardware supporting Vorbis:
-
-
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- [https://helixcommunity.org/projects/xiph/ RealPlayer Plug-In]
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- Other useful links:
