I've been wondering this myself. I copied all my iTunes purchased music videos to my S7 Edge and all 250 of them now show in my gallery.Thanks for the help so far guys! I have a another question if you can help me out.
I use 'Android File Transfer' to drag and drop media files from my Macbook to my S7. It works as attended as video and music appear in their respective apps (VLC, Play Music). My question is, how do I prevent videos from also going into my 'Gallery'? I get a mix of photos and video files which I do not want.