I'd say BOTH!you can start with an external machine, and on another level, introduce a funny out-of-place text that says something like
"oh! silly me. I actually have a rewinder inside myself!"
What if you don't need to rewind them, but you can do it to earn more points when you put them in their place? This way you give the player a choice: place as many movies as fast as possible, or take a risk and waste some time to get more points
And in this way you could let the robot rewind them himself, since it's already a risk
