If the thumbnails are not showing up on Explorer for Mov, Mkv, Avi, Mpeg, etc… there’s a quick fix:

  1. Download Icaros 3.1.1 http://m.majorgeeks.com/files/details/icaros.html
  2. Install and activate Thumbnails for the filetypes.
  3. It should work inmediatly
  4. You can even drag a file and see if its supported: