Some DVD players now remember where you stopped playing a DVD, even if the disk is removed. When you put the disk back in, it reads the disk identifier, looks in its memory to see if it has a previous position for that disk, and (if it does) starts playing from that point.
This is all very well, except for the situation where you have a rental house containing such a DVD player and a selection of DVDs to watch - at the end of the rental period, the remembered positions of the DVDs might not all be at the start, leading to somebody putting on a movie and it unexpectedly starting half way through.
What is needed to solve this problem is some kind of mechanism... for rewinding DVDs!
(Perhaps just a button on the front that says "rewind all" which causes all the remembered positions to be forgotten. Or what our DVD player does when it starts somewhere other than the beginning - putting a "press such-and-such button to start from the beginning".)
Fortunately the problem is rather less severe than the problem of rewinding VHS tapes, so we won't have to remember to rewind rental DVDs.