Wikipedia uses theOgg Vorbis,FLAC andWAV formats for audio, as they are not encumbered by patents (an issue that prompted the decision that MP3 files will not be hosted at Wikipedia). Software supporting Vorbis exists for many platforms...
MozillaFirefox 4,Opera 10.5 andGoogle Chrome 3 (and later versions) each include their own support for Ogg Vorbis files.
As for multimedia players,Winamp can be used to play Ogg Vorbis files. AlthoughiTunes does not natively support Vorbis, Xiph.Org providesa QuickTime component which can be used in players that rely onQuickTime, such as iTunes, on bothMicrosoft Windows andMac OS.DirectShow filters exist to decode Vorbis in multimedia players likeWindows Media Player and others which supportDirectShow.
Various online tools (such asZamzar) are available which let you freely convert one file format into another, and can be useful when you want to upload a file to Wikipedia.