Regenerate infotip movie thumbnail


I have edited the infotip for movies, so that a thumbnail is displayed in the info window. It usually works great, especially with the option to skip over the first black frames.

Although, I noticed that sometimes, the thumbnail is "wrong".

I.e. there's a normal 1st image in the movie, but nonetheless the thumbnail displayed is entirely black.

Is there a way to somehow "force" the application to re-create a movie thumbnail ?

I have already tried clearing the thumbnail cache, and using Shift+F5, to no avail.

Any help or tip appreciated,
Thanks in advance.