ID3

From Wikipedia, the free encyclopedia
  (Redirected from Id3)
Jump to: navigation, search

ID3 is a metadata container most often used in conjunction with the MP3 audio file format. It allows information such as the title, artist, album, track number, and other information about the file to be stored in the file itself.

There are two unrelated versions of ID3: ID3v1 and ID3v2.

Although ID3 is sometimes referred to as a standard, the term applies only in the de facto sense, as no standardization body was involved in its creation nor has such an organization given it a formal approval status.[1]

ID3v1[edit]

After the creation of the MP3 standard, there appeared a problem with storing data about the file. Standalone MP3s didn't have any special method of doing this. In 1996 Eric Kemp had the idea to add a small chunk of data to the audio file, thus solving the problem. The method, now known as ID3v1, quickly became the de facto standard for storing metadata in MP3s.[2] The format was released by Damaged Cybernetics, an underground group that specialized in cracking console gaming systems. There was no identifying information for any of the ROMS, thus an ID tagging system was created to make tracking easier. Eric and associates carried this over into mp3 files. This format was used for a number of file formats unknown at that time.[citation needed]

The ID3v1 tag occupies 128 bytes, beginning with the string TAG. The tag was placed at the end of the file to maintain compatibility with older media players. Some players would play a small burst of static when they read the tag, but most ignored it, and almost all modern players will correctly skip it. This tag allows 30 bytes each for the title, artist, album, and a "comment", four bytes for the year, and a byte to identify the genre of the song from a predefined list of 80 values (Winamp later extended this list to 148 values).

One improvement to ID3v1 was made by Michael Mutschler in 1997. Since the comment field was too small to write anything useful, he decided to trim it by two bytes and use those two bytes to store the track number. Such tags are referred to as ID3v1.1.[2]

Extended tag[edit]

The extended tag is an extra data block before an ID3v1 tag, which extends the title, artist and album fields by 60 bytes each, offers a freetext genre, a one-byte (values 0–5) speed and the start and stop time of the music in the MP3 file, e.g., for fading in. If none of the fields are used, it will be automatically omitted.

Some programs supporting ID3v1 tags can read the extended tag, but writing may leave stale values in the extended block. The extended block is not an official standard, and is only supported by few programs, not including XMMS or Winamp. The extended tag is sometimes referred to as the "enhanced" tag.

Layout[edit]

Strings are either space- or zero-padded. Unset string entries are filled using an empty string.

ID3v1: 128 bytes

Field Length Description
header 3 "TAG"
title 30 30 characters of the title
artist 30 30 characters of the artist name
album 30 30 characters of the album name
year 4 A four-digit year
comment 28[3] or 30 The comment.
zero-byte[3] 1 If a track number is stored, this byte contains a binary 0.
track[3] 1 The number of the track on the album, or 0. Invalid, if previous byte is not a binary 0.
genre 1 Index in a list of genres, or 255

Extended tag (placed before the ID3v1 tag): 227 bytes

Field Length Description
header 4 "TAG+"
title 60 60 characters of the title
artist 60 60 characters of the artist name
album 60 60 characters of the album name
speed 1 0=unset, 1=slow, 2= medium, 3=fast, 4=hardcore
genre 30 A free-text field for the genre
start-time 6 the start of the music as mmm:ss
end-time 6 the end of the music as mmm:ss

ID3v2[edit]

In 1998, a new specification called ID3v2 was created by multiple contributors.[4] Although it bears the name ID3, its structure has virtually no similarity with ID3v1.

ID3v2 tags are of variable size, and usually occur at the start of the file, to aid streaming media. They consist of a number of frames, each of which contains a piece of metadata. For example, the TIT2 frame contains the title, and the WOAR frame contains the URL of the artist's website. Frames can be up to 16MB in length, while total tag size is limited to 256MB. The internationalization problem was solved by allowing the encoding of strings not only in ISO-8859-1, but also in Unicode.

Textual frames are marked with an encoding byte.[5]

$00 – ISO-8859-1 (LATIN-1, Identical to ASCII for values smaller than 0x80).
$01 – UCS-2 (UTF-16 encoded Unicode with BOM), in ID3v2.2 and ID3v2.3.
$02 – UTF-16BE encoded Unicode without BOM, in ID3v2.4.
$03 – UTF-8 encoded Unicode, in ID3v2.4.

However, mojibake is still common when using local encodings instead of Unicode. In particular, some Japanese editors are known to use Shift JIS encoding, which usually has disastrous effects: it will assuredly not work with any standard-compliant software regardless of local settings (since it is not supported by the standard), assuredly not work outside Japan (since Shift JIS has very little support outside of Japan), and will not even work on all Japanese computers even with a specifically non-compliant reader (as it is software-dependent and settings-dependent).

There are 83 types of frames declared in the ID3v2.4.0 specification,[6] and applications can also define their own types. There are standard frames for containing cover art, BPM, copyright and license, lyrics, and arbitrary text and URL data, as well as other things. There are three versions of ID3v2:

  • ID3v2.2 was the first public version of ID3v2. It used three character frame identifiers rather than four (TT2 for the title instead of TIT2). Most of the common v2.3 and v2.4 frames have direct analogues in v2.2. Now this standard is considered obsolete.[7]
  • ID3v2.3 expanded the frame identifier to four characters, and added a number of frames. A frame could contain multiple values, separated with a / character. This is the most widely used version of ID3v2 tags.
  • ID3v2.4 is the latest version published, dated November 1, 2000. Notably, it allows textual data to be encoded in UTF-8, which was a common practice in earlier tags (despite the standard, since it was not supported yet) because it has several noticeable advantages over UTF-16. It uses a null byte to separate multiple values, so the character "/" can appear in text data again. Another new feature allows the addition of a tag to the end of the file before other tags (like ID3v1).

Windows Explorer and Windows Media Player cannot handle ID3v2.4 tags in any version, up to and including Windows 8 / Windows Media Player 12. Windows can understand ID3v2 up to and including version 2.3.[8][9]

ID3v2 Rating tag issue[edit]

There is a loose de facto standard for implementation of song ratings. Most apps will display 0 to 5 stars for any given song, and how the stars are expressed can vary. For instance, when rating a song in iTunes, the rating is not embedded in the tag in the music file, but is instead stored in a separate database that contains all of the iTunes metadata. Other media players can embed rating tags in music files but some software creates its own tag frame or method. As a result, a song which is rated on one media player sometimes won't display the rating when played on other software or mobile device.[citation needed]

However, there is a "Popularimeter" frame in the ID3v2 specification meant for this purpose. The frame is called POPM and Windows Explorer, Windows Media Player, Winamp, foobar2000, media monkey and other software all map roughly the same ranges of 0–255 to a 0–5 stars value for display.

The following list details how windows explorer reads and writes the POPM frame:

  • 224–255 = 5 stars when READ with Windows Explorer, writes 255
  • 160–223 = 4 stars when READ with Windows Explorer, writes 196
  • 096-159 = 3 stars when READ with Windows Explorer, writes 128
  • 032-095 = 2 stars when READ with Windows Explorer, writes 64
  • 001-031 = 1 stars when READ with Windows Explorer, writes 1

Windows Explorer uses the following syntax:

Windows Media Player 9 Series | 255 | 0

The 0 is the play counter portion of POPM as per the ID3v2 POPM specification, which is not to be confused or conflated with the PCNT frame, which is a separate frame meant entirely for playcounts. If an app supports granularity however, it should write 1 for one full star, and then 2–31 would be granular points under one full star. Notably, the ID string Windows uses is not an email address, as called for in the specifications. Further, Windows Explorer and Windows Media Player up to and including Windows 7 and Windows Media Player 12 (possibly beyond)[clarification needed] contain a bug such that, if one were to use them to rate files, any Replay Gain tags one would have will be corrupted.[citation needed]

ID3v2 Chapters[edit]

The ID3v2 Chapter Addendum was published in December 2005 but is not widely supported as yet. It allows users to jump easily to specific locations or chapters within an audio file and can provide a synchronized slide show of images and titles during playback. Typical applications include Enhanced podcasts and it can be used in ID3v2.3 or ID3v2.4 tags.[10]

ID3v2 Embedded Image Extension[edit]

The metadata can also contain images of the following types:[11]

$00     Other
$01     32x32 pixels 'file icon' (PNG only)
$02     Other file icon
$03     Cover (front)
$04     Cover (back)
$05     Leaflet page
$06     Media (e.g. label side of CD)
$07     Lead artist/lead performer/soloist
$08     Artist/performer
$09     Conductor
$0A     Band/Orchestra
$0B     Composer
$0C     Lyricist/text writer
$0D     Recording Location
$0E     During recording
$0F     During performance
$10     Movie/video screen capture
$11     A bright coloured fish
$12     Illustration
$13     Band/artist logotype
$14     Publisher/Studio logotype

ID3v2 Frame Specification (Version 2.3)[edit]

 AENC Audio encryption
 APIC Attached picture
 COMM Comments
 COMR Commercial frame
 ENCR Encryption method registration
 EQUA Equalization (replaced by EQU2 in v2.4)
 ETCO Event timing codes
 GEOB General encapsulated object
 GRID Group identification registration
 IPLS Involved people list (replaced by TMCL and TIPL in v2.4)
 LINK Linked information
 MCDI Music CD identifier
 MLLT MPEG location lookup table
 OWNE Ownership frame
 PRIV Private frame
 PCNT Play counter
 POPM Popularimeter
 POSS Position synchronisation frame
 RBUF Recommended buffer size
 RVAD Relative volume adjustment (replaced by RVA2 in v2.4)
 RVRB Reverb
 SYLT Synchronized lyric/text
 SYTC Synchronized tempo codes
 TALB Album/Movie/Show title
 TBPM BPM (beats per minute)
 TCOM Composer
 TCON Content type
 TCOP Copyright message
 TDAT Date (replaced by TDRC in v2.4)
 TDLY Playlist delay
 TENC Encoded by
 TEXT Lyricist/Text writer
 TFLT File type
 TIME Time (replaced by TDRC in v2.4)
 TIT1 Content group description
 TIT2 Title/songname/content description
 TIT3 Subtitle/Description refinement
 TKEY Initial key
 TLAN Language(s)
 TLEN Length
 TMED Media type
 TOAL Original album/movie/show title
 TOFN Original filename
 TOLY Original lyricist(s)/text writer(s)
 TOPE Original artist(s)/performer(s)
 TORY Original release year (replaced by TDOR in v2.4)
 TOWN File owner/licensee
 TPE1 Lead performer(s)/Soloist(s)
 TPE2 Band/orchestra/accompaniment
 TPE3 Conductor/performer refinement
 TPE4 Interpreted, remixed, or otherwise modified by
 TPOS Part of a set
 TPUB Publisher
 TRCK Track number/Position in set
 TRDA Recording dates (replaced by TDRC in v2.4)
 TRSN Internet radio station name
 TRSO Internet radio station owner
 TSIZ Size (deprecated in v2.4)
 TSRC ISRC (international standard recording code)
 TSSE Software/Hardware and settings used for encoding
 TYER Year (replaced by TDRC in v2.4)
 TXXX User defined text information frame
 UFID Unique file identifier
 USER Terms of use
 USLT Unsynchronized lyric/text transcription
 WCOM Commercial information
 WCOP Copyright/Legal information
 WOAF Official audio file webpage
 WOAR Official artist/performer webpage
 WOAS Official audio source webpage
 WORS Official internet radio station homepage
 WPAY Payment
 WPUB Publishers official webpage
 WXXX User defined URL link frame

Multiple values in v2.3 tags[edit]

The version 2.3 of the standard prescribes that some fields can contain multiple values separated by the "/" character. The fields that can contain multiple values are:

 TPE1 TCOM TEXT TOLY TOPE

ID3v2 Frame Specification (Version 2.4 – delta respect to 2.3)[edit]

 EQUA replaced by the EQU2 frame
 IPLS replaced by the two frames TMCL and TIPL
 RVAD replaced by the RVA2 frame
 TDAT replaced by the TDRC frame
 TIME replaced by the TDRC frame
 TORY replaced by the TDOR frame
 TRDA replaced by the TDRC frame
 TYER replaced by the TDRC frame
 TSIZ deprecated.

New frames

 ASPI Audio seek point index
 EQU2 Equalisation
 RVA2 Relative volume adjustment
 SEEK Seek frame
 SIGN Signature frame
 TDEN Encoding time
 TDOR Original release time
 TDRC Recording time
 TDRL Release time
 TDTG Tagging time
 TIPL Involved people list
 TMCL Musician credits list
 TMOO Mood
 TPRO Produced notice
 TSOA Album sort order
 TSOP Performer sort order
 TSOT Title sort order
 TSST Set subtitle

Multiple values in v2.4 tags[edit]

Version 2.4 of the specification prescribes that the text fields (all the fields starting with a T except TXXX) can contain multiple values separated by a null character. The null character is the one represented by the termination code for the character encoding used.

Editing ID3 tags[edit]

ID3 tags may be edited in a variety of ways. On some platforms the file's properties may be edited by viewing extended information in the file manager. Additionally most audio players allow editing single or groups of files. Editing groups of files is often referred to as "batch tagging". There are also specialized applications, called taggers, which concentrate specifically on editing the tags and related tasks. Some, such as puddletag offer advanced features such as advanced batch tagging or editing based on regular expressions.

Implementation in non-mp3s and alternatives[edit]

ID3 tags were designed with MP3 in mind, so they would work without problems with MP3 and MP3Pro files. However, the tagsets are an independent part of the MP3 file and should be usable elsewhere. In practice, the only other format which widely uses ID3v2 tags is AIFF, where the tag is stored inside an IFF chunk named "ID3". The same could be accomplished in WAV, but isn't. The only tagging system in wide usage for WAV is the Broadcast Wave Format, stored as a RIFF chunk. Windows media ASF files (WMA, WMV) have their own tagging formats but also support ID3 Tags embedded as attributes.[12] MP4 also allows the embedding of an ID3 tag,[13] and this is widely supported, especially in Apple's iTunes, which uses MP4 standards in its audio and video file formats. Other container-based formats use their own tagging formats. An example of this is Ogg, which uses Vorbis comments. Adding ID3 tags to these would break the container structure. Earlier versions of Winamp such as 2.xx have been proven able to add ID3v1 and ID3v2 tags to MP1 and MP2 files.

See also[edit]

References[edit]

  1. ^ ID3 History page
  2. ^ a b Practical Common Lisp, p. 335.
  3. ^ a b c The track number is stored in the last two bytes of the comment field. If the comment is 29 or 30 characters long, no track number can be stored.
  4. ^ ID3v2 Contributors
  5. ^ id3v2-00 - ID3.org
  6. ^ "ID3v2.4.0 Native Frames". Retrieved 2012-12-27. 
  7. ^ Nilsson, Martin. "ID3 Developer Information". ID3.org. Retrieved 9 April 2011. 
  8. ^ Bright, Peter (28 October 2012). "Music and Video in Windows 8: a work in progress". arstechnica.com. Retrieved 2012-10-29. 
  9. ^ "Microsoft support community". 11 January 2011. 
  10. ^ Newell, C. (2 December 2005). "ID3v2 Chapter Frame Addendum". ID3.org. Retrieved 2008-02-06. 
  11. ^ ID3 Tag Version 2.3.0
  12. ^ "Windows Media Developer Center: ID3 Tag Support". Microsoft Developer Network. Microsoft. Retrieved 2010-03-24. 
  13. ^ The 'MP4' Registration Authority

External links[edit]