DecMoon has asked for the wisdom of the Perl Monks concerning the following question:

Hi, i've got a problem with package MP3::Tag When I create a new file with a new tag, no problem appears and I can use my beautiful TAG in iTunes or other apps, no problem

But when I try to change some things my script don't retreave anything

#!/usr/bin/perl

use Data::Dumper;
use MP3::Tag;
use utf8;
use strict;

binmode STDOUT, ":utf8";
binmode STDERR, ":utf8";

MP3::Tag->config(write_v24 => 1);

my $audio_file = '/home/decmoon/tmp/test.mp3';
my $name = 'Test tagv2';

my $mp3 = MP3::Tag->new("$audio_file");
print Dumper(\$mp3);

my $id3v1 = exists $mp3->{ID3v1} ? $mp3->{ID3v1} : $mp3->new_tag("ID3v
+1");
$id3v1->title("$name");
$id3v1->write_tag();

my $id3v2 = exists $mp3->{ID3v2} ? $mp3->{ID3v2} : $mp3->new_tag("ID3v
+2");
#                       my $id3v2 = $mp3->{ID3v2};
print Dumper(\$id3v2);
print Dumper(\$id3v2->get_frame_ids);
$id3v2->add_frame("TIT2", $name);
$id3v2->write_tag();
print Dumper(\$id3v2->get_frame_ids);
$mp3->close();
my $mp3 = MP3::Tag->new("$audio_file");
my $id3v2 = exists $mp3->{ID3v2} ? $mp3->{ID3v2} : $mp3->new_tag("ID3v
+2");
print Dumper(\$id3v2->get_frame_ids);
$mp3->close();


exit;

[download]

And output :

$VAR1 = \bless( {
                   'ofilename' => '/home/decmoon/tmp/test.mp3',
                   '__proxy' => bless( [
                                         ${$VAR1}
                                       ], 'MP3::Tag::__proxy' ),
                   'filename' => bless( {
                                          'filename' => '/home/decmoon
+/tmp/test.mp3',
                                          'parent' => ${$VAR1}->{'__pr
+oxy'}
                                        }, 'MP3::Tag::File' ),
                   'abs_filename' => '/home/decmoon/tmp/test.mp3'
                 }, 'MP3::Tag' );
$VAR1 = \bless( {
                   'frame_start' => 0,
                   'revision' => 0,
                   'data_size' => 0,
                   'footer_size' => 0,
                   'flags' => {},
                   'major' => 3,
                   'frame_major' => 3,
                   'tag_data' => '',
                   'tagsize' => 45622,
                   'buggy_padding_size' => 0,
                   'version' => '3.0',
                   'mp3' => bless( {
                                     'parent' => bless( [
                                                          bless( {
                                                                   'ID
+3v1' => bless( {
                                                                      
+                 'mp3' => ${$VAR1}->{'mp3'},
                                                                      
+                 'genre' => '',
                                                                      
+                 'track' => '',
                                                                      
+                 'title' => 'Test tagv2',
                                                                      
+                 'genreID' => 255,
                                                                      
+                 'comment' => '',
                                                                      
+                 'year' => '',
                                                                      
+                 'artist' => '',
                                                                      
+                 'new' => 1,
                                                                      
+                 'changed' => 1,
                                                                      
+                 'album' => ''
                                                                      
+               }, 'MP3::Tag::ID3v1' ),
                                                                   'of
+ilename' => '/home/decmoon/tmp/test.mp3',
                                                                   '__
+proxy' => ${$VAR1}->{'mp3'}->{'parent'},
                                                                   'ID
+3v2' => ${$VAR1},
                                                                   'fi
+lename' => ${$VAR1}->{'mp3'},
                                                                   'ab
+s_filename' => '/home/decmoon/tmp/test.mp3'
                                                                 }, 'M
+P3::Tag' )
                                                        ], 'MP3::Tag::
+__proxy' ),
                                     'filename' => '/home/decmoon/tmp/
+test.mp3'
                                   }, 'MP3::Tag::File' )
                 }, 'MP3::Tag::ID3v2' );
$VAR1 = \{};
$VAR1 = \{
            'TIT2' => 'Title/songname/content description'
          };
$VAR1 = \{};

[download]

tagv1 seems ok, but not tagv2. So, question, why my 1st and 3rd dumpers for get_frame_ids arent empty ? Or mre precisely, why $mp3->{ID3v2} is always undef?
Thanks

Replies are listed 'Best First'.
Re: Question about MP3::Tag and undef id3v2
by poj (Abbot) on Sep 05, 2017 at 20:18 UTC

    See MP3::Tag, try adding get_tags(). 

    my $mp3 = MP3::Tag->new($audio_file);
$mp3->get_tags();

    [download]
    poj
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      Ok, that's it, I missed that line. Thank you ;)
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Re: Question about MP3::Tag and undef id3v2
by tdlewis77 (Sexton) on Sep 05, 2017 at 17:02 UTC

    Could it be because you commented out the assignment?

    #                       my $id3v2 = $mp3->{ID3v2};
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[d/l]
      Hmm, no, it's commented because there is no id3v2 : 
      $VAR1 = \undef;
Can't call method "get_frame_ids" on an undefined value at ./test.pl l
+ine 26.

      [download]
      That's why I do my $id3v2 = exists $mp3->{ID3v2} ? $mp3->{ID3v2} : $mp3->new_tag("ID3v2");
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[d/l]
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        G'day DecMoon,

        Welcome to the Monastery.

        These are lines 25 and 26 in the code you posted: 

        print Dumper(\$id3v2);
print Dumper(\$id3v2->get_frame_ids);

        [download]

        The first line of output you show ($VAR1 = \undef;) is telling you that $id3v2 is undef (i.e. it's undefined).

        So, "$id3v2->get_frame_ids" (in line 26) is equivalent to "undef->get_frame_ids". That's effectively what the second line of output you show is telling you.

        You'll need to do something with your assignment to $id3v2. I'm unfamiliar with the MP3::Tag module, so I'm not really in a position to advise you what that "something" might be. Options could include: checking for definedness; setting a default value; skipping some part of the code if it's not defined; or something completely different.

        — Ken

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