Auto generate thumbnails for watch folders?

I find that thumbnails for videos in watch folders are not generated until after a player accesses the folder new files are in.

Can Mezzmo make the thumbnail when it finds new files?

Yes, Mezzmo looks for and finds the files when you actually access the folder - it doesn't watch over them constantly as that would take quite a bit of CPU resources to do that. Once a new file is found, a thumbnail is generated for it, but by that time the device already displayed the file (without a thumbnail), so that's why you need to re-access the folder to see the thumbnail.