I have a replay saved on my computer, but no way that I know of to convert it to a .mp4 or format otherwise viewable by a computer without starcraft, or a .rep viewer [some can be found on the internet]. Searching both SEN and google turned up nothing at all, which tells me two things:
1) that nobody has a converter [unlikely, especially since I'm sure I'm not the first person who has thought of this],
2) that .rep files are impossible to save as .mp4 or similar format,
or [and most likely]
3) that this is a problem so elementary that I'm overlooking the basic premise of it [much as someone new to scmdraft might not know how to use the text trigedit instead of classic trigedit].
If anyone could provide a link to the converter I would appreciate it.

The tools you'll need:

StarCraft, you can find that here:
C:\Program Files\Starcraft\StarCraft.exe

FRAPS:
http://www.fraps.com/download.php

Generic video to mp4 converter:
http://google.com/search?num=100&q=convert+mp4+free


In case you didn't get my joke, what you are asking to do is equivalent to turning a text file of lyrics into a mp3 song.

IIRC, .rep files tell the AI what to do, in order to replicate the game. They aren't actually recorded videos, which is why replays glitch very often.