I did exactly the same. I had to update OS X to El Capitan from Yosemite in order to get the videos playing again.Same here, recently updated now none of my Mac`s will play any video bought on iTunes. Am going to download iTunes and reinstall. Apple`s software just gets worse...
Update: reinstalling iTunes 12.3.1 did nothing, nor is anything forthcoming from Apple is effecting all my Mac`s More users with the same issue here, conveniently upgrading to 10.11 resolves, equally that completely breaks my workflow.
Q-6
I did exactly the same. I had to update OS X to El Capitan from Yosemite in order to get the videos playing again.
Wait! There is iTunes 13.3 or do you mean 12.3?I did the opposite uninstalled iTunes 12.3.1 installed iTunes 13.3, reran the 10.10.5 OS X installer iTunes now plays all video. I don't want OS X 10.11 as it breaks to many applications still being a WIP by Apple.
Q-6
I have the same issue.
Thanks for posting your solution. Worked like a charm.
I think it's the latest security update that caused the problem. I had iTunes 12.3.1.23 and worked without any problem - until I installed the latest security update. Then nothing worked.