Revision as of 09:30, 6 July 2005

Introduction

Ogg Vorbis (www.vorbis.com) is a fully open, non-proprietary, patent-free (subject to speculation), and royalty-free, general-purpose compressed audio format for mid to high quality (8khz-48.0kHz, 16+ bit, polyphonic) audio and music at fixed and variable bitrates from 16 to >256 kbps/channel. This places vorbis in the same competitive class as audio representations such as MPEG-4 (AAC), and similar to, but higher performance MP3, twinvq (VQF), WMA and PAC.

Vorbis is the first of a planned family of Ogg multimedia coding formats being developed as part of Xiph.org's ogg multimedia project.

Informal listening test suggests Vorbis to be comparable to MPEG-4 AAC at most bitrates and MPC at 128 kbps. Transparency is generally reached at about 150-170 kbps (-q 5) (with some exceptions). The encoder is reasonably young and unoptimized, so further improvements can always be expected.

Unfortunately, Xiph.org has failed to improve Vorbis at a steady rate since its initial 1.0 release in July 2002 (due to other developement projects and time constraints). Since then development has been lead by other coders such as Garf and Aoyumi. Aoyumi's AoTuV series of encoders was incorporated into the September 2004 release of 1.1, which brought about the first quality improvements across the board for 2 years. Currently Aoyumi is working on AoTuv Beta 4 and future releases.

Vorbis has had success with many recent video game titles employing Vorbis as opposed to MP3 (with Epic Games' Unreal Tournament 2003 and Unreal Tournament 2004, the PC port of Microsoft's Halo and Uru being notable examples).

Pros

Free (as in speech), Open Source and claimed to be patent free
Good all-round performance (>48 kbps - a leading codec at 128 kbps)
Well written specs
Several portable hardware players
Suitable for internet-streaming (via Icecast and other methods)
Fully gapless playback
High potential for further tuning
Structured to allow the design for a hybrid filterbank.

Cons

Limited official development (third-party developement is always encouraged)
Current implementations are more computationally intensive to encode and decode than MP3 (Vorbis 2.0 seeks to overcome this limitation by slimlining the encoder)
Multichannel input mappings for 5.1, Ambisonic-B, and other config have no channel coupling and aren't tuned (expect sub-optimal results until code is improved).

Technical details used in compression

Psychoacoustics masking exploited via an (ATH model)
Masking curves derived from emperically adjusted set of Ehmer Curves
Multiple block sizes for window switching (varies for different modes, powers or two only)
Modified Discrete Cosine Transform (MDCT) is used for noise analysis.
Fast Fourier Transform (FFT) is used for tonal analysis.
Customly designed window function similiar to the sine window (good sidelobe rejection).
The noise-floor uses piecewise linear representation to encode the spectral envelope curve.
Advanced coupled stereo modes (point/phase stereo and lossless)
Vector quantization is used for coding the noise-floor and residue backend using trained codebooks.
Huffman coding is used to minimize vector codeword redundancy.

Software

Encoders

Oggenc official command-line encoder (Win32/Posix).
OggdropXPd advanced drag-and-drop encoder by John33 (Win32)
foo_vorbisenc vorbis encoder library for Foobar2000 (Win32)

Decoders

Ogg123 for Unix systems (GPL), a very simple to use command-line player. (Win32/Posix)
OggDec for Windows, by John33, a very featureful command line decoder. (Win32)
QuickTime Component (Allows playback in QuickTime/iTunes) (Win32)
CoreVorbis (DirectShow) (Win32)
illiminable Ogg Directshow Filters (Also plays Speex, Theora and FLAC) (Win32)

Supported Digital Audio Players

The following list contains some players that support Vorbis playback. A longer list can be found at xiph's wiki.

iRiver H-Series
MPIO H-Series
Rio Karma
iAudio M3, U2, G3, 5
Neuros
Samsung Yepp YP-T6, YP-T7, YP-C1, YP-F1

External links

The following links contain information surrounding the Ogg Vorbis codec that can be found on Hydrogenaudio and elsewhere throughout the web.

@@ Line 29: / Line 29: @@
 * Psychoacoustics masking exploited via an ([[ATH]] model)
 * Masking curves derived from emperically adjusted set of [http://www.zainea.com/masking2.htm Ehmer Curves]
-* Multiple block sizes for window switching (varies for different modes)
+* Multiple block sizes for window switching (varies for different modes, powers or two only)
 * Modified Discrete Cosine Transform ([[MDCT]]) is used for noise analysis.
 * Fast Fourier Transform ([[FFT]]) is used for tonal analysis.
 * Customly designed window function similiar to the sine window (good sidelobe rejection).
+* The noise-floor uses piecewise linear representation to encode the spectral envelope curve.
 * Advanced coupled stereo modes ([http://us.xiph.org/ogg/vorbis/doc/stereo.html point/phase stereo] and lossless)
 * [[Vector quantization]] is used for coding the noise-floor and residue backend using ''trained'' codebooks.