"Is this a MIDI audio file? Where did you find it?
Control click and choose "Open with" and pick QuickTime Player."
Yes it is a MIDI file it was on my grandfathers windows 98 se computer and I found it a few years ago when we had my old windows me and the 98 networked. I tried opening it in Quicktime but not luck it says it is not a movie file.
I haven't seen one in 12 years.
Last hope:
Duplicate the file (Command-D) and change the file extension from .rmi to .mid and see if QuickTime will open it.