RMVB is a RealMedia Variable Bitrate file. This is one of the newer formats from Real for publishing video files, which is quickly becoming a popular format for Anime and Asian movie titles because of smaller file sizes and lower bitrates with exceptional quality compared to DivX, which has long been the standard for trading videos online. There are two options for playing back the file.
You can either playback the file by downloading and installing the latest version of RealPlayer, which is free despite all the shenanigans the Real site puts you through trying to get you to try the SuperPass. The second option is to use Real Alternative which plays back RealMedia files outside of RealPlayer.
After installing either of these apps, you still need to associate the RMVB file type with the player because it isn't recognized by default. Right-click the file and choose Open from the right-click menu. Choose Select the program from a list and click OK.
Choose RealPlayer or Real Alternative and leave the box checked next to Always use the selected program to open this kind of file.
When you click on any RMVB file, it should automatically launch RealPlayer to playback the file.
[from Jake Ludington's website]
Last update: 08:56 PM Saturday, May 13, 2006