Yours Truly answers: As of January 2005, Windows Media Player (WMP) does not natively support industry-standard MPEG-4. Despite its increasing popularity for its superior compression algorithms, I would assume that Microsoft will not move quickly to add native support for MPEG-4 in WMP. This is in part because the underlying audio codec is AAC (Advanced Audio Codec) that was developed primarily by Apple Computer. All music purchased at Apple’s iTunes store is encoded in AAC for use in the iPod.
 
Microsoft states “Windows Media Player does not support the playback of the .mp4 file format. You can play back .mp4 media files in Windows Media Player when you install DirectShow-compatible MPEG-4 decoder packs. DirectShow-compatible MPEG-4 decoder packs include the Ligos LSX-MPEG Player and the EnvivioTV.”
 
The problem solved? Not quite. LSX-MPEG Player is no longer available! EnvivioTV is not freeware, as their web site states “ EnvivioTV can only be purchased by Envivio customers. It is available as a plug-in for the Apple QuickTime player, the RealNetworks player, and the Windows Media player.”
 
So, how would we add MPEG-4 decoding capability to a Windows PC free of charge? Get QuickTime Player for movies and iTunes for audio.