iTunes and external HDD

I have moved some downloaded movies to an external drive wanting to give me more space of the internal HDD of my Mac Mini. My question is this: Can i safely delete the movies from my internal HDD (iTunes Library)? Should i then want to watch the copy located on the External drive, how do i do that? When I try to open the movie, the app VLC (a video Player) opens but the movie doesn't play. Thank you in advance, cheers and beers :confused:

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