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7 Ogg Vorbis comment field specification
10 <em>Last update to this document: February 9, 2001</em><p>
12 The text comment header is the second (of three) header packets that
13 begin a Vorbis bitstream. It is meant for short, text comments,
14 not arbitrary metadata; arbitrary metadata belongs in a
15 metadata stream (usually an XML stream type).<p>
17 <h2>Comment use rationale</h2>
19 The comment field is meant to be used much like someone jotting a
20 quick note on the bottom of a CDR. It should be a little information to
21 remember the disc by and explain it to others; a short, to-the-point
22 text note that need not only be a couple words, but isn't going to be
23 more than a short paragraph. The essentials, in other words, whatever
24 they turn out to be, eg:
27 "Honest Bob and the Factory-to-Dealer-Incentives, _I'm Still Around_,
28 opening for Moxy Fruvous, 1997"
33 The comment header logically is a list of eight-bit-clean vectors; the
34 number of vectors is bounded to 2^32-1 and the length of each vector
35 is limited to 2^32-1 bytes. The vector length is encoded; the vector
36 is not null terminated. In addition to the vector list, there is a
37 single vector for vendor name (also 8 bit clean, length encoded in 32
38 bits). Libvorbis currently sets the vendor string to "Xiphophorus
39 libVorbis I 20010119".<p>
41 The comment vectors are structured similarly to a UNIX environment.
42 That is, comment fields consist of a field name and a field value and
46 comment[0]="ARTIST=me";
47 comment[1]="TITLE=the sound of vorbis";
50 <h2>Content vector format</h2>
53 <li>A case-insensitive field name that may consist of ASCII 0x20 through
54 0x7D, 0x3D ('=') excluded. ASCII 0x41 through 0x5A inclusive (A-Z) is
55 to be considered equivalent to ASCII 0x61 through 0x7A inclusive
58 <li>The field name is immediately followed by ASCII 0x3D ('='); this
59 equals sign is used to terminate the field name.
61 <li>0x3D is followed by 8 bit clean UTF-8 field contents to the end of
67 Below is a proposed, minimal list of standard filed names with a
68 description of intended use. No single or group of field names is
69 mandatory; a comment header may contain one, all or none of the names
72 <dt>TITLE<dd>Track name
74 <dt>VERSION<dd>The version field may be used to differentiate multiple
75 version of the same track title in a single collection. (e.g. remix info)
77 <dt>ALBUM<dd>The collection name to which this track belongs
79 <dt>TRACKNUMBER<dd>The track number of this piece if part of a specific larger collection or album
81 <dt>ARTIST<dd>Track performer
83 <dt>ORGANIZATION<dd>Name of the organization producing the track (i.e.
86 <dt>DESCRIPTION<dd>A short text description of the contents
88 <dt>GENRE<dd>A short text indication of music genre
90 <dt>DATE<dd>Date the track was recorded
92 <dt>LOCATION<dd>Location where track was recorded
94 <dt>COPYRIGHT<dd>Copyright information
96 <dt>ISRC<dd>ISRC number for the track; see <a href="http://www.ifpi.org/online/isrc_intro.html">the ISRC intro page</a> for more information on ISRC numbers.
100 <h3>Implications</h3>
103 Field names should not be 'internationalized'; this is a
104 concession to simplicity not an attempt to exclude the majority of
105 the world that doesn't speak English. Field *contents*, however,
106 are represented in UTF-8 to allow easy representation of any language.
108 We have the length of the entirety of the field and restrictions on
109 the field name so that the field name is bounded in a known way. Thus
110 we also have the length of the field contents.
112 Individual 'vendors' may use non-standard field names within
113 reason. The proper use of comment fields should be clear through
114 context at this point. Abuse will be discouraged.
116 There is no vendor-specific prefix to 'nonstandard' field names.
117 Vendors should make some effort to avoid arbitrarily polluting the
120 Field names are not required to be unique (occur once) within a
121 comment header. As an example, assume a track was recorded by three
122 well know artists; the following is permissible, and encouraged:
124 ARTIST=Dizzy Gillespie
133 The comment header comprises the entirety of the second bitstream
134 header packet. Unlike the first bitstream header packet, it is not
135 generally the only packet on the second page and may not be restricted
136 to within the second bitstream page. The length of the comment header
137 packet is [practically] unbounded. The comment header packet is not
138 optional; it must be present in the bitstream even if it is
139 effectively empty.<p>
141 The comment header is encoded as follows (as per Ogg's standard
142 bitstream mapping which renders least-significant-bit of the word to be
143 coded into the least significant available bit of the current
144 bitstream octet first):
148 Vendor string length (32 bit unsigned quantity specifying number of octets)
151 Vendor string ([vendor string length] octets coded from beginning of string to end of string, not null terminated)
153 <li>Number of comment fields (32 bit unsigned quantity specifying number of fields)
155 <li>Comment field 0 length (if [Number of comment fields]>0; 32 bit unsigned quantity specifying number of octets)
158 Comment field 0 ([Comment field 0 length] octets coded from beginning of string to end of string, not null terminated)
160 <li>Comment field 1 length (if [Number of comment fields]>1...)...
163 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()
166 <a href="http://www.xiph.org/">
167 <img src="white-xifish.png" align=left border=0>
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171 Ogg is a <a href="http://www.xiph.org">Xiphophorus</a> effort to
172 protect essential tenets of Internet multimedia from corporate
173 hostage-taking; Open Source is the net's greatest tool to keep
174 everyone honest. See <a href="http://www.xiph.org/about.html">About
175 Xiphophorus</a> for details.
178 Ogg Vorbis is the first Ogg audio CODEC. Anyone may
179 freely use and distribute the Ogg and Vorbis specification,
180 whether in a private, public or corporate capacity. However,
181 Xiphophorus and the Ogg project (xiph.org) reserve the right to set
182 the Ogg/Vorbis specification and certify specification compliance.<p>
184 Xiphophorus's Vorbis software CODEC implementation is distributed
185 under the Lesser/Library GNU Public License. This does not restrict
186 third parties from distributing independent implementations of Vorbis
187 software under other licenses.<p>
189 OggSquish, Vorbis, Xiphophorus and their logos are trademarks (tm) of
190 <a href="http://www.xiph.org/">Xiphophorus</a>. These pages are
191 copyright (C) 1994-2001 Xiphophorus. All rights reserved.<p>