This is a simple binding for libextractor http://gnunet.org/libextractor/. 
It allows you to read metadata from a wide number of file types.

It can be used this way
  require 'extractor'
  metadata = Extractor.extract('happy.mp3')
  puts metadata['mimetype']
  puts metadata['artist']
Sometimes there will be more than one entry for a metadata type. For example, an mp3 may have two artists. If this is the case then you might have
  metadata['artist'] == ['Puff Daddy', 'The Family']