Quote Originally Posted by Useless Hacker
AFAIK, you don't need a license to use MP3 files, it is just the software for decoding them which requires a license, but if you are using DirectSound I understand that Microsoft have already payed on your behalf.
Actually no, that's virtually never the case. Windows contains all sorts of technologies licensensed from other companies and you will still need your own license to be legally allowed to use it in your own programs.