RMVB Format and Ubuntu

Playing Real Media File

RMVB format : RMVB is a proprietary format plays mp3, rm, ra, rv, wma, wmv, ogg, aac, and more. RealPlayer for Linux is based on the open source Helix player. RealPlayer supports RealAudio, RealVideo, WMA, WMV, MP3, Ogg Vorbis and Theora, H263, AAC and more. Get ready for accelerated video, full screen playback, and a lot more to enjoy.

http://www.real.com/linux/ Download the debian package for ubuntu and install it. This should help you with RMVB formats.