Problem

You want to save (capture) a RealAudio or RealVideo stream to a file for later
viewing or listening.

Keywords

Real, RealAudio, RealVideo, capture, record, streaming, stream, rip, ripping,
mplayer, Linux.

Solution

mplayer -noframedrop -dumpfile out.rm -dumpstream rtsp://url/to/file.rm

(Michael Carr notes that passing a -bandwidth N option, where N is
your available bandwidth may considerably speed up the download; the mplayer
manual seems to be unclear about it being bits or bytes, though.)

When the download is done you can watch or listen to out.rm with
a media player, like realplay or mplayer.