1. Use something like Realaudio-to-Wav Recorder to encode the Real Audio to WAV (PCM/16bit/44.1kHz).

http://www.geocities.com/rawavrecorder/

2. Now use TMPGEnc:

First close wizard, then load in a Template (use Load button - right corner). Choose one that's best for your video - NTSC (29.97 fps), NTSCFilm (23.976 fps) or PAL (25 fps)

Video source: should be - original RMVB file
Audio source: should be - the WAV file that was created.

START to encode.

http://www.digital-digest.com/dvd/downlo...pgenc.html

TMPGEnc and Realaudio-to-Wav Recorder are freeware programs, but there are other ways of doing the conversion.

EO Video is another one that can do it. It is not totally free though. You only get a short trial period before it must be purchased:

http://www.eo-video.com/