Gmod Mp3 player and songs downloaded from Youtube?

I have the DVDVideosoft free youtube downloader. It’s very handy. But the gmod mp3 player won’t play songs downloaded from youtube… I click it and nothing happens…
Is there a way to fix it, or not?

Come one, anybody?

Faulty codec, perhaps?

[editline]20th March 2011[/editline]

try using zamzar.com