So that is, if the videos where in a subfolder in the roms folder they were scraped as roms also, you must have checked the option to scan subfolders when imported the games. What I would do is to use the Audit tool and in the list that shows you the results just click in the title of the File Path column, that should leave all the games whose rom files are in the videos subfolder together in the list so you can easily select all of them and delete the games from the database, that will also delete the media of those games. Besides that if you have checked the option "Allow deleting roms when deleting games" in Tools->Options->General, when you delete the games it will give you the option to delete the roms (Videos in this case). Hope this helps.