iTunes (version 12.3.1.23) doesn't play my TV Shows/Movies!
A lot of people are experiencing the same issue. It seems to have occurred after the most recent security update (for Yosemite 10.10.5 this is security update 2015-005. There is a discussion on apple support but nobody from Apple has bothered to respond yet. Deauthorization, moving files in and out of library, re-downloading videos from the iTunes store, etc. have not helped anyone. System logs indicate there is an error and those people who've posted the log passages on the error show that it seems to be the same among those experiencing the problem. Some people have advised downgrading to an earlier iTunes version. However, I'm figuring since a lot of people are experiencing it, Apple will have to come up with a fix that will cause less problems than a downgrade...