[vbat99]

Many thanks, vbat99.

I will look into this, but please note: DISC or Media Stub files source should not be added to the Offline Folder. Instead, The source directory will be added to the Movie Folders tab if not already added.

Hmmm, I had understood completely wrong. But, what for is the "Offline Folder", if not for the offline movies / DVDs?

So I first suggest to remove I:\Eigene Dateien\Videos\Filme auf DVD from your Offline Movie Folder, and add it to your Movie Folders list.

I have done it like that: http://i.imgur.com/77j0OH4.png
But there does not appear any movie after prressing "Search" or "Refresh".

Ah no, sorry, it seems to work. There is such a black bar: http://i.imgur.com/hTYoFeb.png. Obviously MC is scraping.

The Offline Movie Folder was for offline movies that Media Companion created. MC would create a 10 second video saying something like Insert your disc
See This documentation

While what you are trying to do is call Media Stubs which are xml files that XBMC reads with info on what disc you need to insert.
On the Media Stubs tab, allocate your offline stubs folder,
Enter the movie title, ie Avatar
Select the Disc Format
If you wish, type an alternative title for the movie.
And if you want a different message displayed in XBMC, change the Media Message.
Click save, change to browsing tab and search.
This discussion may be of insight. We seem to be lacking documentation of Media Stubs