MP3::ID3v1Tag - Edit ID3v1 Tags from an Audio MPEG Layer 3.

  use MP3::ID3v1Tag;

  $mp3_file = new MP3::ID3v1Tag("filename.mp3");
  $mp3_file->print_tag();

  if($mp3_file->got_tag()) {
     $mp3_file->set_title($title); 
     $save_status = $mp3_file->save();
  }

  if $mp3_file->got_tag() {
     $mp3_file->print_tag();
  }

  $title     = $mp3_file->get_title();
  $artist    = $mp3_file->get_artist();
  $album     = $mp3_file->get_album();
  $year      = $mp3_file->get_year();
  $genre     = $mp3_file->get_genre();
  $genre_num = $mp3_file->get_genre_num();
  $comment   = $mp3_file->get_comment();

  $mp3_file->set_title("New Title");
  $mp3_file->set_artist("New Artist");
  $mp3_file->set_album("New Album");
  $mp3_file->set_year(1999);
  $mp3_file->set_genre("Blues"); 
  # Or use the genre numbers ->
  $mp3_file->set_genre_num(0);

 $mp3_file->remove_tag() if $mp3_file->got_tag();

 You could access all the components directly for a read only loop such
as the following

package MP3::ID3v1Tag;
require 5.004;

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# $Id: ID3v1Tag.pm,v 2.11 2000/09/01 00:26:18 sander Exp $
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

use strict;
use vars qw(@ISA @EXPORT @EXPORT_OK);
use Carp;
use IO::File;

require Exporter;
@ISA = ('Exporter');
@EXPORT = qw();
@EXPORT_OK = qw();

$MP3::ID3v1Tag::VERSION = do { my @r = (q$Revision: 2.11 $ =~ /\d+/g); $r[0]--;sprintf "%d."."%02d" x $#r, @r }; # must be all one line, for MakeMaker

## Revision and debuging
$MP3::ID3v1Tag::revision = '$Id: ID3v1Tag.pm,v 2.11 2000/09/01 00:26:18 sander Exp $ ';
my $DEBUG = 0;

## SOME USEFULL CONSTANTS.
## see http://www.dv.co.yu/mpgscript/mpeghdr.htm
##     by Predrag Supurovic <mpgtools@dv.co.yu>
##     http://www.id3.org/
my $DefaultClass = 'MP3::ID3v1Tag';

@MP3::ID3v1Tag::id3_genres_array = (
			'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'
		       );

my $c = 0;
%MP3::ID3v1Tag::id3_genres = map {$_ => $c++ } @MP3::ID3v1Tag::id3_genres_array;

## A silly print routine useful for debugging.
sub debug {
  my($self,$message) = @_;
  print STDERR "$message\n" if $DEBUG;
}

## Constructor for Object of Module
sub new {
  my($class,$mp3_file,$readonly) = @_;
  my $self = {};
  $readonly = 0 unless defined($readonly);
  $self->{FileHandle} = new IO::File;
  if( -w $mp3_file || !$readonly)  {
    $self->{FileHandle}->open("+<${mp3_file}") or (warn("Can't open ${mp3_file}: $!") and return undef);
    $self->{readonly} = 0;
  } else {
    $self->{FileHandle}->open("<${mp3_file}") or (warn("Can't open ${mp3_file}: $!") and return undef);
    $self->{readonly} = 1;
  }
  $self->{filename} = $mp3_file;
  $self->{tag} = ();
  bless($self, ref $class || $class || $DefaultClass);
  my $initialized = $self->init();
  return $self;
}

# We provide a DESTROY method so that the autoloader
# doesn't bother trying to find it.
sub DESTROY {
  my($self) = @_;
  $self->{FileHandle}->close();
}

## Generic routine to see if this MP3 has an ID3v1Tag
sub got_tag {
  my($self) = @_;
  return ($self->find_tag_id3v1())?1:0;
}

## Some generic initialization
## Find the headers and be ready for questions.
sub init {
  my($self) = @_;
  my $bytestring ="";
  $bytestring = $self->find_tag_id3v1();
  if(!defined($bytestring)) {
    return 0;
  } else {
    $self->decode_tag_id3v1($bytestring);
  }
  return 1;
}

## Print a Genre Chart for easy reference.
sub print_genre_chart {
  my($self,$columns) = @_;
  $columns = 3 if ($columns <=0);
  my $i = 0;
  for(my $i = 0;$i < $#MP3::ID3v1Tag::id3_genres_array+1 ; $i += $columns) {
    for(my $j = 0;($j < $columns) && ($i + $j < $#MP3::ID3v1Tag::id3_genres_array+1); $j++) {
      printf("%2s. %-20s",$i + $j, $MP3::ID3v1Tag::id3_genres_array[$i + $j]);
    }
    print "\n";
  }
}

## ID3v1 TAG at the END of the File.
## Talks about ID3v2 being at the beginning of the file.
sub find_tag_id3v1 {
  my($self) = @_;
  my($bytes,$line);
  ## MusicMatch has their data here aswell, but they are planning
  ## on supporting ID3 to prevent issues.
  $self->{FileHandle}->seek(-128,SEEK_END); # Find the last 128 bytes
  while($line = $self->{FileHandle}->getline()) { $bytes .= $line; }
  return undef if $bytes !~ /^TAG/; # Must have Tag Ident to be valid.
  return $bytes;
}


## Decode the ID3v1 Tag into useful tidbits.
sub decode_tag_id3v1 {
  my($self,$buffer) = @_;
  ## Unpack the Audio ID3v1
  (undef, @{$self->{tag}}{qw/title artist album year comment genre_num/}) =
    unpack('a3a30a30a30a4a30C1', $buffer);
  
  ## Clean em up a bit
  foreach (sort keys %{$self->{tag}}) {
    if(defined($self->{tag}{$_})) {
      $self->{tag}{$_} =~ s/\s+$//;
      $self->{tag}{$_} =~ s/\0.*$//;
      $self->debug(sprintf("ID3v1: %s = ", $_ ) . $self->{tag}{$_});
    }
  }
  $self->{tag}{'genre'} = $MP3::ID3v1Tag::id3_genres_array[$self->{tag}{'genre_num'}];
  $self->debug(sprintf("ID3v1: %s = ", 'genre' ) . $self->{tag}{'genre'});
}

sub encode_tag_id3v1 {
  my($self) = @_;
  ## Visit the beginning of the id3 tag if it exists
  return 0 if($self->{readonly});
  if(!defined($self->find_tag_id3v1())) {
    $self->debug("Going to Append Tag");
    # No Tag
    $self->{FileHandle}->seek(0,SEEK_END); # Find EOF
  } else {
    $self->debug("Going to Re-write Tag.");
    $self->{FileHandle}->seek(-128,SEEK_END); # Find the last 128 bytes
  }
  $self->{tag}{'genre_num'} = 255 if(!defined($self->{tag}{'genre_num'}));
  $self->{FileHandle}->print(pack("a3a30a30a30a4a30C1", 
			  'TAG',
			  $self->{tag}{'title'},
			  $self->{tag}{'artist'},
			  $self->{tag}{'album'},
			  $self->{tag}{'year'},
			  $self->{tag}{'comment'},
			  $self->{tag}{'genre_num'}));
  $self->{FileHandle}->flush();
  return 1;
}

sub remove_tag {
  my($self) = @_;
  return 0 if($self->{readonly});
  return 1 if(!defined($self->find_tag_id3v1()));
  my $filesize = (stat($self->{FileHandle}))[7];
  $self->debug("Removing Tag: File size = $filesize");
  my $success = truncate($self->{FileHandle},($filesize - 128));
  $filesize = (stat($self->{FileHandle}))[7];
  $self->debug("Removed Tag : File size = $filesize");
}

sub save {
  my($self) = @_;
  return $self->encode_tag_id3v1();
}
## Print the Tag to default File Handler (usually STDOUT)
sub print_tag {
  my($self) = @_;

  if(defined($self->{tag})) {
    foreach (sort keys %{$self->{tag}}) {
      print(sprintf("%-10s = ",$_ ) . $self->{tag}{$_} . "\n");
    }
  } else {
    print "No ID3v1 Tag Found\n";
  }
}


##
sub get_title {
  my($self) = @_;
  return $self->{tag}{'title'};
}
sub set_title {
  my ($self,$title) = @_;
  $self->{tag}{'title'} = $title;
}

##
sub get_artist {
  my($self) = @_;
  return $self->{tag}{'artist'};
}
sub set_artist {
  my($self,$artist) = @_;
  $self->{tag}{'artist'} = $artist;
}

##
sub get_album {
  my($self) = @_;
  return $self->{tag}{'album'};
}
sub set_album {
  my($self,$album) = @_;
  $self->{tag}{'album'} = $album;
}

##
sub get_year {
  my($self) = @_;
  return $self->{tag}{'year'};
}
sub set_year {
  my($self,$year) = @_;
  $self->{tag}{'year'} = $year;
}

sub get_comment {
  my($self) = @_;
  return $self->{tag}{'comment'};
}
sub set_comment {
  my($self,$comment) = @_;
  $self->{tag}{'comment'} = $comment;
}

sub set_genre {
  my($self,$genre) = @_;
  my $genre_num = $MP3::ID3v1Tag::id3_genres{$genre};
  if($genre_num >= 0 && $genre_num <= $#MP3::ID3v1Tag::id3_genres_array) {
    $self->{tag}{'genre'} = $genre;
    $self->{tag}{'genre_num'} = $genre_num;
  }
}

sub get_genre {
  my($self) = @_;
  return $self->{tag}{'genre'};
}

sub set_genre_num {
  my($self,$genre_num) = @_;
  if( $genre_num >= 0 && $genre_num <= $#MP3::ID3v1Tag::id3_genres_array) {
    $self->{tag}{'genre_num'} = $genre_num;
    $self->{tag}{'genre'} = $MP3::ID3v1Tag::id3_genres_array[$genre_num];
    return 1;
  }
  return 0;
}
  
sub get_genre_num {
  my($self) = @_;
  return $self->{tag}{'genre_num'};
}
  
## Gives direct access to the %tag hash
sub tag {
  my($self,$key) = @_;
  return wantarray ? keys %{$self->{tag}}: $self->{tag}{$key};
}

  
1;