Ripping subtitles from avis?

I was wondering if a software existed that could rip the subtitles from avi files. I mean I don’t wanna take down the burned in subtitles but I would love to have them in a txt separetedly too. I know I can not make them disapear (which is no problem since I have the raws of the files) but I would need the subtitle files for the raws to make them as optional subtitles for dvd!

So, is there a software that can do this or all I can do is spend hours with typing (watching screen and typing in a txt what I can read on the picture) and timing the text ( in the dvd creator) for the dvd all by my self?