I have tried following simple filter:
Type matches folder
contains (.avi|.mov)
which doesn't highlight the folder with the assigned label. What am i doing wrong?
Contains searches for text inside files. It doesn't do anything with folders.
Is there another way then? I know how to highlight various file types, but not, how to label the containing folder.
There's no easy or efficient way. It would require listing the contents of every folder.
Similar to showing folder sizes. If you're already doing that then it wouldn't add much overhead as the data would already be cached, but you'd probably need something like a script column that lists all the extensions found below each folder.
Ok, that's what i thought, thanks. Maybe it would be a good idea to include this function someday? The use case here is, that i sometimes have short video clips in my photo collection, which always are in a subfolder. But the idea with the script column sounds promising, as it would do the same job.
Maybe the ancient FolderSelector helps?!
Thanks, tbone. I have just tried it, & it's also useful for this task. Cool! 
One question, how would i search for multiple types? Like (avi|mov|mp4)?
Multiple extensions cannot be done with the version you have, but maybe try the one in the linked thread I updated seconds ago. o) The syntax you suggested should work, it's a regex search now.
It's perfect, tbone, thanks again!