Auto generate Thumbnails

Hi all,

got a question regarding thumbnail creation.
Basically, I have video files in several folders.
I browse them using the thumbnails XBMC creates.
However, I have to go into each folder first, wait for XBMC to create the thumbs, and then move on to the next folder.

Is there are a script or something, which I can give the path of the folder to scan for files to create thumbnails for, recursively.

Found a few hits on google for the same query, but none with an answer.

Many thanks,
derchris