OGG VORBIS

http://www.vorbis.com

OGG Vorvis es un nuevo formato de compresión de audio, es comparable a otros formatos empleados para este propósito como MP3, VQF, AAC. La enorme diferencia que posee con todos ellos es que es completamente GRATIS, y de código abierto.

OGG es el nombre del mayor proyecto que está llevando a cabo "Xiph.org" (www.wiph.org), que es una fundación que se dedica al desarrollo de proyectos con software libre, y en este proyecto en concreto, está volcando todos los esfuerzos para que se imponga como estándar de audio en Internet de dominio público. EL nombre OGG viene de una maniobra táctica que se empleaba en un juego de red llamado "Netrek".

El proyecto OGG nace en 1993 bajo el nombre de "squish", pero luego se descubre que ese nombre se correspondía con una marca registrada de un sistema de transporte de correo, así que se cambia el nombre a OGG.

Xiph.org, en la actualidad se encuentra desarrollando cuatro proyectos de compresión relacionados al audio:

Vorbis es el nombre específico de un esquema de compresión de audio que fue diseñado para estar incluido en OGG.

OGG Vorbis fue diseñado para reemplazar completamente todos los formatos de audio patentados, es decir que se puede codificar absolutamente toda tu música con OGG Vorvis y nunca más tener que volver atrás.

CARACTERISTICAS:

Es posible convertir cualquier formato de audio a Ogg Vorvis, sin embargo, al convertirlos desde ciertos formatos, ya lo haces con pérdida de calidad, como sería el caso de hacerlo desde MP3, pues recuerda que este es inferior, es decir que si tomas un archivo .mp3 y lo conviertes a .ogg, lograrás reducir su tamaño, pero la calidad será la misma que con mp3, o inclusive peor, pues ogg vorvis, recortará a su vez cierta información de entrada, en realidad, el proceso será que ogg vorvis, descomprimirá el archivo .mp3 a un formato tipo WAV y lo recomprimirá empleando su algoritmo, si no tienes otra opción que esta, puedes encontrar varios productos que lo hacen en: http://freshmeat.net/search/?q=convert%20ogg%20mp3

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Existen dos grandes clases de algoritmos de compresión:

Existe una cierta escala de medición de "calidad" a la cual se le asignan valores entre-1 y 10, en la misma se asocia al valor 1: 64 kbps, al 5: 160kbps y al 10: 400kbps. Para la mayoría de la gente, un valor muy cercano a la calidad de un CD estaría alrededor del 5 y sin perder estereofonía, podría ser un 6. La calidad por defecto que suele venir configurado en los diferentes compresores suele ser 3, tasa que proporciona buena relación calidad/tamaño. Si se hace una relación entre mp3 y ogg, un archivo de "igual" calidad, se correspondería a una valocidad de 110 kbps en oog y 128 kbps en mp3

 

 

CAMPO COMENTARIOS DE OGG VORBIS:

 

Ogg Vorbis I format specification: comment field and header specification

Last update to this document: July 16, 2002

Overview

The Vorbis text comment header is the second (of three) header packets that begin a Vorbis bitstream. It is meant for short, text comments, not arbitrary metadata; arbitrary metadata belongs in a separate logical bitstream (usually an XML stream type) that provides greater structure and machine parseability.

The comment field is meant to be used much like someone jotting a quick note on the bottom of a CDR. It should be a little information to remember the disc by and explain it to others; a short, to-the-point text note that need not only be a couple words, but isn't going to be more than a short paragraph. The essentials, in other words, whatever they turn out to be, eg:

"Honest Bob and the Factory-to-Dealer-Incentives, _I'm Still Around_, opening for Moxy Fruvous, 1997"

Comment encoding

Structure

The comment header logically is a list of eight-bit-clean vectors; the number of vectors is bounded to 2^32-1 and the length of each vector is limited to 2^32-1 bytes. The vector length is encoded; the vector contents themselves are not null terminated. In addition to the vector list, there is a single vector for vendor name (also 8 bit clean, length encoded in 32 bits). Libvorbis currently sets the vendor string to "Xiph.Org libVorbis I 20020717".

The comment header is decoded as follows:

  1) [vendor_length] = read an unsigned integer of 32 bits
  2) [vendor_string] = read a UTF-8 vector as [vendor_length] octets
  3) [user_comment_list_length] = read an unsigned integer of 32 bits
  4) iterate [user_comment_list_length] times {

       5) [length] = read an unsigned integer of 32 bits
       6) this iteration's user comment = read a UTF-8 vector as [length] octets

     }

  7) [framing_bit] = read a single bit as boolean
  8) if ( [framing_bit]  unset or end of packet ) then ERROR
  9) done.

Content vector format

The comment vectors are structured similarly to a UNIX environment variable. That is, comment fields consist of a field name and a field value and look like:

comment[0]="ARTIST=me"; 
comment[1]="TITLE=the sound of Vorbis"; 

Field names

Below is a proposed, minimal list of standard filed names with a description of intended use. No single or group of field names is mandatory; a comment header may contain one, all or none of the names in this list.

TITLE
Track/Work name
VERSION
The version field may be used to differentiate multiple versions of the same track title in a single collection. (e.g. remix info)
ALBUM
The collection name to which this track belongs
TRACKNUMBER
The track number of this piece if part of a specific larger collection or album
ARTIST
The artist generally considered responsible for the work. In popular music this is usually the performing band or singer. For classical music it would be the composer. For an audio book it would be the author of the original text.
PERFORMER
The artist(s) who performed the work. In classical music this would be the conductor, orchestra, soloists. In an audio book it would be the actor who did the reading. In popular music this is typically the same as the ARTIST and is omitted.
COPYRIGHT
Copyright attribution, e.g., '2001 Nobody's Band' or '1999 Jack Moffitt'
LICENSE
License information, eg, 'All Rights Reserved', 'Any Use Permitted', a URL to a license such as a Creative Commons license ("www.creativecommons.org/blahblah/license.html") or the EFF Open Audio License ('distributed under the terms of the Open Audio License. see http://www.eff.org/IP/Open_licenses/eff_oal.html for details'), etc.
ORGANIZATION
Name of the organization producing the track (i.e. the 'record label')
DESCRIPTION
A short text description of the contents
GENRE
A short text indication of music genre
DATE
Date the track was recorded
LOCATION
Location where track was recorded
CONTACT
Contact information for the creators or distributors of the track. This could be a URL, an email address, the physical address of the producing label.
ISRC
ISRC number for the track; see the ISRC intro page for more information on ISRC numbers.

Implications

              ARTIST=Dizzy Gillespie 
              ARTIST=Sonny Rollins 
              ARTIST=Sonny Stitt 

Encoding

The comment header comprises the entirety of the second bitstream header packet. Unlike the first bitstream header packet, it is not generally the only packet on the second page and may not be restricted to within the second bitstream page. The length of the comment header packet is [practically] unbounded. The comment header packet is not optional; it must be present in the bitstream even if it is effectively empty.

The comment header is encoded as follows (as per Ogg's standard bitstream mapping which renders least-significant-bit of the word to be coded into the least significant available bit of the current bitstream octet first):

  1. Vendor string length (32 bit unsigned quantity specifying number of octets)
  2. Vendor string ([vendor string length] octets coded from beginning of string to end of string, not null terminated)
  3. Number of comment fields (32 bit unsigned quantity specifying number of fields)
  4. Comment field 0 length (if [Number of comment fields]>0; 32 bit unsigned quantity specifying number of octets)
  5. Comment field 0 ([Comment field 0 length] octets coded from beginning of string to end of string, not null terminated)
  6. Comment field 1 length (if [Number of comment fields]>1...)...

This is actually somewhat easier to describe in code; implementation of the above can be found in vorbis/lib/info.c:_vorbis_pack_comment(),_vorbis_unpack_comment()


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http://www.xiph.org/Ogg is a Xiph.org Foundation effort to protect essential tenets of Internet multimedia from corporate hostage-taking; Open Source is the net's greatest tool to keep everyone honest. See About the Xiph.org Foundation for details.

Ogg Vorbis is the first Ogg audio CODEC. Anyone may freely use and distribute the Ogg and Vorbis specification, whether in a private, public or corporate capacity. However, the Xiph.org Foundation and the Ogg project (xiph.org) reserve the right to set the Ogg Vorbis specification and certify specification compliance.

Xiph.org's Vorbis software CODEC implementation is distributed under a BSD-like license. This does not restrict third parties from distributing independent implementations of Vorbis software under other licenses.

Ogg, Vorbis, Xiph.org Foundation and their logos are trademarks (tm) of the Xiph.org Foundation. These pages are copyright (C) 1994-2002 Xiph.org Foundation. All rights reserved.