Sometimes, Gnome doesn’t show the thumbnails, whether for videos or pictures.  It can be by the lack of a thumbnailer, but almost because the location of the thumbnails folder has changed !

Now, the thumbnails are stored under the .cache folder.

To solve the problem, just follow these steps:

  1. Go to your cache folder : cd .cache
  2. Create a symbolic  link to the folder (.)thumbnails in your home folder:  ln -s ../.thumbnails thumbnails
  3. You now get a link in .cache to thumbnails:thumbnails -> ../.thumbnails/

Open Nautilus and see the previews appear !