This program plays mp4 audio/video files either locally from file or remotely streamed via RTSP/RTP. In addition to local mp4 files, it can also play mp3, aac, wav, divx, and mp4v files. The streaming function uses IETF standards and so is compatible with a number of video servers, including Apples QuickTime Server (aka Darwin Streaming Server). User settings are remembered and saved in ~/.gmp4player_rc.
If you are attempting to stream from an on-demand server and there is a firewall between the player and server, you probably will need to select the "Use RTP over RTSP (TCP)" option from the "Network" menu.