multimedia player for various audio and video formats
http://www.videolan.org/vlc/download-windows.html

VLC (initially VideoLAN Client) is a highly portable multimedia player for various audio and video formats (MPEG-1, MPEG-2, MPEG-4, DivX, mp3, ogg...) as well as DVDs, VCDs, and various streaming protocols. It can also be used as a server to stream in unicast or multicast in IPv4 or IPv6 on a high-bandwidth network.

• It is a free cross-platform media player
• It supports a large number of multimedia formats, without the need for additional codecs
• It can also be used as a streaming server, with extended features (video on demand, on the fly transcoding)