<< The easiest way would be to locate the team who wrote Windows Media Player, go to their Rights Management coders and say "tell me how to unlock this or I will cut your (insert valuable protruberance of your choice here) off".
Seriously, no. WMA's 'advantages' prevent you from doing such presumptious things. Bastards. Keep it MP3 - Fight the power!
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I wouldn't mind rights management being implemented sensibly - for example, I don't mind SCMS - if it wasn't being decided for us by money-grabbing lawyers, the lazy music industry and the politicians in their pockets.
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chill out man, you can disable rights management from the gui.
Noriaki, the easiest way i can think of is to convert it to wav and encode it back to mp3 just like you woulddo the opposite. but im curious why dont you want it in wma format (read: whats wrong with the file?)