So how to generate thumbnails for these containers?

I know that the install of "DivX Plus Tech Preview: MKV on Windows 7" does it for MKV. But I think that only some registry changes are really necessary and I want it for other containers.

If it's possible to avoiding the install of (always bloated) codecs packs it would be nice... Maybe only installing ffdshow or essential and separated codecs.

(some time ago I have try reg files for vista without success...)

Update: I have installed Win7codecs & tweaked a little its settings and I got almost everything I want. (I have also re-installed the relevant part of the divx plus tech preview to get something else than an all black preview for MKV)

• Find a cleaner & lighter method
• Almost all my rmvb and mov files got an all black preview (installing real media/quick time alternative doesn't help, is it the same with the officials?)
• With almost all containers (avi, mkv, ogm, mpg), I have (few) random files that don't get the preview. I could play them in WMP or another player and don't have found a pattern in the codecs used. All wmv, flv and mp4 have previews but I have less files in these containers.

(I clear my thumbnails cache to test them)

More generally I would like to understand how windows handle the containers & codecs to generate the previews.

And a software that let me choose arbitrarily the pictures previewed would be convenient too