Vorbis

From Example Problems
Jump to navigation Jump to search
This page is about the audio compression codec. For the Discworld character, see minor Discworld characters.

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. It is often mistakenly called just Ogg (in turn mistakenly written in uppercase, "OGG") due to either the file container Ogg, the file extension .ogg or possibly even the MIME content type application/ogg used for Vorbis playback in streaming.

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 version is 1.1.1 released on 2005-06-27. Source code for this release is available from the official Vorbis web site, while many Windows binaries can be downloaded at Rarewares.

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 2005, is still the most prevalent lossy audio format.

In the commercial sector, Vorbis is being used in many newer video game titles (such as Epic Games' Unreal Tournament 2003 and Unreal Tournament 2004, the PC port of Microsoft's Halo and Uru being notable examples). The increasing number of hardware players that support Vorbis is encouraging its growth as of July 2004; see the compatible hardware 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' increasing popularity is the number of music websites using it, like 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:

Listening tests [1] have attempted to find the best quality lossy audio codecs at certain bitrates. The tests 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.

Based on this, Vorbis can be considered a high quality codec. For most applications Vorbis is a good codec to use, and could be considered superior to other modern codecs because it is patent-free and produces smaller files than some other codecs at equivalent quality.

Technical details

Ogg quality levels
Quality Bitrate
-q-2 (only aoTuV beta4 and later) ~32 kbit/s
-q-1 ~45 kbit/s (original vorbis) ~48 kbit/s (aoTuV beta4 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 current encoder as of September 2004 will produce output from 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. 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. 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, although no encoder has implemented this feature yet.

Vorbis streams can be encapsuled in other media container formats aside Ogg. More common choices include 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 [2]. 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 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

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 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.

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.
Some devices that play Ogg Vorbis files:

  • All iRiver harddisk players (except H10 and N10 and 180T) support Ogg Vorbis. Most of the flash-memory players will play Ogg Vorbis without a firmware upgrade. (Note: Some models are unable to deal with variable bitrates that fall below 96 kbps and therefore are only suitable for -q5 or higher encoded files)
  • The Neuros (site) portable player released a firmware upgrade offering Ogg Vorbis support after a beta testing period in the latter half of 2003. Firmware versions 1.45 and newer support Ogg Vorbis.
  • Rio Karma, an mp3 player which supports both Ogg Vorbis and FLAC.
  • The Jens of Sweden MP-130, MP-120, MP-400 and MP-450 (site) supports Ogg Vorbis.
  • The Xclef HD800 [3] supports Ogg Vorbis amongst other formats.
  • Cowon iAudio M3 [4], iAudio X5, iAudio 5 (up to -Q10), iAudio U2, and iAudio G3 [5]
  • Samsung YH-J70, YP-60V, and the Samsung YP-MT6 series supports Ogg right out of the box. Also does the Samsung Yepp YP-T7 and the Yepp YP-C1 series
  • KiSS DVD-Players (site) are supporting Ogg Vorbis, MP3 and WMA. Some models have an Ethernet port allowing to stream audio and video from a PC on the network or listen to Internet radio.
  • The Muzio JM-200, 250, 300, H1000 (site) all support Ogg Vorbis (through firmware upgrade for the 200/250 models).
  • The Mpeye HTS-200 offers native Ogg Vorbis support (q1-q10) (site)
  • The TrekStor i.Beat Organix is also advertised to support Ogg Vorbis. It is availabe with flash memory in sizes 256 MB, 512 MB and 1GB. But caution: The product TrekStor i.Beat vision doesn't seem to support Ogg Vorbis.
  • Apple's iPod is able to play Ogg Vorbis using iPodLinux and MPD, although this is an unofficial "hack" and will void your warranty.

Software

Again, the VorbisSoftwarePlayers node at the xiph.org wiki has an up-to-date list of Vorbis-supporting software for all operating systems. You can test these players using the list of Vorbis audio streams available at [6].

Ogg Vorbis can be played using these (and other) players:

There are also plug-ins on the Microsoft website which let Windows Media Player play Ogg Vorbis.

At the moment, third party companies have to create plug-ins to make itunes able to read Ogg Vorbis. But hopefully in the near future, Apple will make it compatible themselves. However, this is unlikely as Apple wants to encourage people to use their own audio format - AAC which they claim to be better than MP3.

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

Trivia

"Ogg" is not named after the witch Nanny Ogg in Terry Pratchett's Discworld books; see Ogg for the correct definition. However, "Vorbis" is named after another Discworld character, High Priest Vorbis in Small Gods.

See also

Listening tests

External links

ast:Ogg ca:Ogg Vorbis da:Ogg Vorbis de:Vorbis es:Ogg Vorbis eo:Ogg Vorbis eu:Ogg Vorbis fr:Ogg Vorbis it:Ogg Vorbis he:Ogg Vorbis hu:Vorbis nl:Ogg Vorbis ja:Ogg Vorbis no:Ogg Vorbis pl:Vorbis pt:Vorbis ru:Ogg vorbis fi:Ogg Vorbis sv:Ogg Vorbis tr:Ogg Vorbis uk:Ogg vorbis