VideoLan (VLC Media Player) is a multimedia and DVD player for Linux, BeOS, BSD, MacOS X ...
VLC Media player (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.
Playing back .MP4 H.264 encoded movies:
Use VideoLAN which has a built in .MP4 reader and H.264 decoder