You could also restore the library backup from MC17, to your MC18 installation.
In case it fails, it should be easy to change the Media Sub Type tag to video, instead of files. This is done in the action window. Bottom left side. Tag and click the top left icon on the window, changing it to "Show all tags". There you can change the Media Type as well as Media Sub Type. You can also add columns to any view, and edit the fields directly there by clicking two times slowly in that field. Alternatively use F2 to edit a field. MC tries to identify imported files, but it will sometimes fail if you import lots of different media.