Cross-platform media player and streaming server. "VLC media player 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." My partner says that VLC Media Player, a FREE open source tool, is the "best media player in the world. I use it all the time. Plays everything without plugins and fuss." VLC Media Player works on Mac, GNU/Linux and Windows.
VLC Media Tutorials: If you're going to try out VLC, these tutorials might be a good way to start: "...a series of steps on how to convert video/audio, etc."