Storage data just does not add up

Hi, Just finished transferring all music, video, podcasts etc over from my windows laptop to my RMBP.
In Itunes, I have a total of about 7GB of audio including music and podcasts and a total of about 5GB of movies, going by what the bottom of the iTunes window says.
However if I go to "about this mac" and then storage, it says that I have 24GB of movies and 25GB of Music. Just does not add up.

I can't see that the rest is from the OS, so how can I decrease this down to the right amount? Or what could be causing it?

Thanks in advance!

 

Thanks, installed that. I started with my photos due to some being replicated, but that also got the 'other' category right down, but as soon as i added them back, the other storage section shot right back up again.

Looking on that app, movies and music seems to have been copied to another location. I transferred the music into a file on the music/movies section and dragged it over to iTunes. Would this have caused another copy of every song and film?