Ze stranek http://www.live.com/mplayer/:
Recently, however, MPlayer was updated so that it can play RealAudio/RealVideo "rtsp://" streams. It does this by first checking whether the URL ends with ".rm" or ".ra". If it does, it handles it as a special case, not using the LIVE.COM Streaming Media support. Otherwise, it uses the LIVE.COM Streaming Media support, as usual.