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How to read/write ID3 tags in MP3 files

The thing that makes MPEG Layer 3 files good (besides their size:) are ID3 tags. Thanks to them you can save information about the song. Here's the ID3 tag structure and information on reading/modifying them. Enjoy!

The ID3 tag is saved in the last 128 bytes of a MPEG Layer 3 file. It starts with a 'TAG' string. If this string is absent that means that ID3 information has been removed. But don't worry - all you have to do is append it to the file. In newer versions of Delphi if you are going to use this code you may want to use the packed keyword with arrays and records.

// The MPEG Layer 3 ID3 tag structure:
 type
   ID3Struct = record
     Signature: array [0..2] of Char; { Should be: 'TAG' }
     Title, Artist, Album: array [0..29] of Char;
     Year: array [0..3] of Char;
     Comment: array [0..29] of Char;
     Genre: Byte;
   end;
 
 // Here's the genre (Max. 256 entries).
 const
   ID3Genre : array [0..126] of string = ('Blues', 'Classic Rock',
     'Country', 'Dance', 'Disco', 'Funk', 'Grunge', 'Hip-Hop',
     'Jazz', 'Metal', 'New Age', 'Oldies', 'Other', 'Pop', 'R&B',
     'Rap', 'Reggae', 'Rock', 'Techno', 'Industrial', 'Alternative',
     'Ska', 'Death Metal', 'Pranks', 'Soundtrack', 'Euro-Techno',
     'Ambient', 'Trip-Hop', 'Vocal', 'Jazz+Funk', 'Fusion', 'Trance',
     'Classical', 'Instrumental', 'Acid', 'House', 'Game', 'Sound Clip',
     'Gospel', 'Noise', 'AlternRock', 'Bass', 'Soul', 'Punk',
     'Space', 'Meditative', 'Instrumental Pop', 'Instrumental Rock',
     'Ethnic', 'Gothic', 'Darkwave', 'Techno-Industrial', 'Electronic',
     'Pop-Folk', 'Eurodance', 'Dream', 'Southern Rock', 'Comedy',
     'Cult', 'Gangsta', 'Top 40', 'Christian Rap', 'Pop/Funk',
     'Jungle', 'Native American', 'Cabaret', 'New Wave', 'Psychadelic',
     'Rave', 'Showtunes', 'Trailer', 'Lo-Fi', 'Tribal', 'Acid Punk',
     'Acid Jazz', 'Polka', 'Retro', 'Musical', 'Rock & Roll',
     'Hard Rock', 'Folk', 'Folk-Rock', 'National Folk', 'Swing',
     'Fast Fusion', 'Bebob', 'Latin', 'Revival', 'Celtic', 'Bluegrass',
     'Avantgarde', 'Gothic Rock', 'Progressive Rock', 'Psychedelic Rock',
     'Symphonic Rock', 'Slow Rock', 'Big Band', 'Chorus', 'Easy Listening',
     'Acoustic', 'Humour', 'Speech', 'Chanson', 'Opera', 'Chamber Music',
     'Sonata', 'Symphony', 'Booty Bass', 'Primus', 'Porn Groove',
     'Satire', 'Slow Jam', 'Club', 'Tango', 'Samba', 'Folklore',
     'Ballad', 'Power Ballad', 'Rhythmic Soul', 'Freestyle', 'Duet',
     'Punk Rock', 'Drum Solo', 'Acapella', 'Euro-House', 'Dance Hall' );
 
 // This is the ID3 Tag read code:
 procedure ReadID3Tag;
 var
   fMP3: file of Byte;
   Tag: ID3Struct;
 begin { ReadID3Tag }
   try
     (* sFileName - (string) The full file name with path. *)
     AssignFile(fMP3, sFileName);
     Reset(fMP3);
     try
       Seek(fMP3, FileSize(fMP3) - 128);
       BlockRead(fMP3, Tag, SizeOf(Tag))
     finally
 
     end; { try }
 
   finally
     CloseFile(fMP3)
   end; { try }
   if fMP3.Signature<>'TAG' then
   begin
 
     { Doesn't have an ID3 tag }
   end { fMP3.Signature<>'TAG' }
   else
   begin
 
     { do something with the tag }
   end; { not (fMP3.Signature<>'TAG') }
 end; { ReadID3Tag }
 
 
 (* WriteID3Tag() function
   **
   ** Copyright (c) 2000 Jacob Dybala (m3Rlin)
   ** Freeware.
   **
   ** Created : January 7 2000
   ** Modified: January 7 2000
   ** Please leave this copyright notice.
   *)
 procedure WriteID3Tag(id3NewTag: ID3Struct; sFileName: string);
 var
   fMP3: file of Byte;
   Tag: ID3Struct;
 begin { WriteID3Tag }
   try
     AssignFile(fMP3, sFileName);
     Reset(fMP3);
     try
       Seek(fMP3, FileSize(fMP3) - ID3OffsetFromEnd);
       BlockRead(fMP3, Tag, SizeOf(Tag));
       if fMP3.Signature='TAG' then
         { Replace old tag }
         Seek(fMP3, FileSize(fMP3) - ID3OffsetFromEnd)
       else
         { Append tag to file because it doesn't exist.
           Cannot use Append() function. It's only for text files. }
         Seek(fMP3, FileSize(fMP3));
       BlockWrite(fMP3, id3NewTag, SizeOf(id3NewTag))
     finally
 
     end; { try }
 
   finally
     CloseFile(fMP3)
   end; { try }
 end; { WriteID3Tag }
 
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