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pradeep 7May2007 14:43

Read/Write MP3 Tags with Perl
 

Introduction



If you're like most people, you probably have a bunch of MP3s scattered around your hard disk. And if you're like most people, you probably also have on your to-do list a plan to inspect and catalog them so that you know exactly what you're listening to. It's just that you haven't gotten around to it yet.

Well, with a little help from Perl, it's possible for you to finally cross that item off your list. CPAN comes with an MP3::Tag module, which provides ready-made tools to read and extract metadata from MP3 files, making it a simple matter to identify the title, artist, and genre of a particular MP3 track. This can then be used with Perl's file functions to efficiently (and automatically) build an index of all your MP3 content. And if you'd like to, you can even edit the file metadata with built-in module functions.

This article will discuss both functions, showing you how to use the MP3::Tag module to read and write MP3 file metadata. It assumes that you have a working Perl installation with the MP3::Tag module installed; if you don't have this module, you can download it from CPAN.

Reading MP3 tags



Let's start with the basics: reading ID3 tags embedded in MP3 files. Snippet A is a simple example, which demonstrates how this may be done with MP3::Tag:

Snippet A
Code: Perl

#!/usr/bin/perl
   
   use MP3::Tag;
   $mp3 = MP3::Tag->new('track1.mp3'); # create object
   
   $mp3->get_tags(); # read tags
   
   if (exists $mp3->{ID3v1}) { # print track information
   print "Filename: $filename\n";
   print "Artist: " . $mp3->{ID3v1}->artist . "\n";
   print "Title: " . $mp3->{ID3v1}->title . "\n";
   print "Album: " . $mp3->{ID3v1}->album . "\n";
   print "Year: " . $mp3->{ID3v1}->year . "\n";
   print "Genre: " . $mp3->{ID3v1}->genre . "\n";
   }
   
   $mp3->close(); # destroy object

Nothing too complicated here. First, a new MP3::Tag object is created, with the filename and location of the MP3 file passed to the object constructor as an argument. Next, the object's get_tags() method is used to read the metadata embedded in the file headers and represent it as object properties. These properties can then be accessed and printed in the normal way. Here's a sample of the output:
Code:

  Filename: track1.mp3
  Artist: Udit Narayan
  Title: Pehla Nasha
  Album: Joh Jeeta Wohi Sikander
  Year: 1992
  Genre: Soundtrack

This capability makes it particularly easy to do what I promised I'd show you at the beginning of this article--create a printable catalog of all your music files. All you need to do is place the code above in a loop, run it on all your *.mp3 files, and format the output for easy readability. Snippet B shows you how.

Snippet B
Code: Perl

#!/usr/bin/perl
   
   use MP3::Tag; # import module
   
   @files = <*.mp3>; # find MP3 files in current directory
   
   # loop over file list
   # print tag information
   foreach (@files) {
   $mp3 = MP3::Tag->new($_);
   $mp3->get_tags();
   
   if (exists $mp3->{ID3v1}) {
   print $_, "\t", $mp3->{ID3v1}->artist, "\t", $mp3->{ID3v1}->title, "\n";
   }
   
   $mp3->close();
   }

In this case, the list of MP3 files in the current directory is stored in the @files array. A foreach loop then iterates over this array, using the get_tags() method to retrieve and print detailed metadata for each file.

And there you have it--an automatically generated MP3 catalog! As you add new music files to your collection, simply rerun the script above, and they will automatically show up in the catalog listing. Isn't that neat?

Writing MP3 tags



Of course, it doesn't just stop there--you can just as easily use MP3::Tag to write new metadata to an MP3 file. Snippet C is an example of how you might do this.

Snippet C
Code: Perl

#!/usr/bin/perl
 
   use MP3::Tag;
   $mp3 = MP3::Tag->new('track2.mp3'); # create object
   
   $mp3->get_tags(); # read tags
   
   if (exists $mp3->{ID3v1}) { # save track information
   $mp3->{ID3v1}->title("Roothke Humse Kahi");
   $mp3->{ID3v1}->artist("Joh Jeeta Wohi Sikander");
   $mp3->{ID3v1}->album("Various");
   $mp3->{ID3v1}->year("1992");
   $mp3->{ID3v1}->write_tag();
   }
   
   $mp3->close(); # destroy object

If you look closely, you'll see some similarities between this and the previous scripts. As before, the first step is to initialize an object of the MP3::Tag class by passing the object constructor the name of the MP3 file you wish to alter. The get_tags() method is then used to retrieve the current file metadata. Altering this metadata becomes as simple as assigning new values to the appropriate object properties and then saving the new values to the file with a call to the write_tag() method.

Of course, in the real world, it's highly likely that you won't be hard-wiring metadata into your script. Instead, you're more likely to need an interactive application, one that prompts the user for artist, track, and title information and then writes this data to the MP3 file. Luckily, this application is easy to build, knowing what you know now about MP3::Tag. Take a look at Snippet D.

Snippet D
Code: Perl

#!/usr/bin/perl
   
   use MP3::Tag;
   
   $filename = shift; # get filename from command line
   $mp3 = MP3::Tag->new($filename);
   $mp3->get_tags(); # read tags
   
   print "Enter track title: "; # prompt for title
   chomp ($title = <>);
   
   print "Enter artist: "; # prompt for artist
   chomp ($artist = <>);
   
   print "Enter album: "; # prompt for album name
   chomp ($album = <>);
   
   print "Enter year: "; # prompt for year
   chomp ($year = <>);
   
   if (exists $mp3->{ID3v1}) { # save track information
   $mp3->{ID3v1}->title($title);
   $mp3->{ID3v1}->artist($artist);
   $mp3->{ID3v1}->album($album);
   $mp3->{ID3v1}->year($year);
   $mp3->{ID3v1}->write_tag();
   }
   
   $mp3->close(); # destroy object

When invoked on the command line, this script expects to be passed the name of the MP3 file to be edited. It then instantiates a new MP3::Tag object for this file and retrieves available tag information. Next, a series of prompts is generated, for the user to interactively enter title, artist, album, and year information. This data is then written back to the MP3 file via the write_tag() method discussed previously.

The scripts above should have given you some idea of what you can do with MP3::Tag and perhaps even helped you organize your music collection.


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