Of course the easiest & most assured answer is to take along a portable fully self-contained DVD player. Many laptop computers can also play DVD movies. But as I have an eye for most things AV I have noticed that most cabin TVs on most ships DO have AV inputs in the front so you can plug in your camcorder, a dvd player or a lot of other things. I remember playing back my camcorder on the TV on Pride of Aloha last year.
I am the editor, but I also speculate, ask questions and play devil's advocate. I reserve the right to change my mind.