If you sign up for and install Movies Anywhere, your iTunes library becomes available, along with your Amazon, Vudu and Google Play libraries. There is no cost. I even found that most of my videos are also available via YouTube, although I noticed the resolution there is only SD.
There are some studios that are not yet participating in MA, but since it has Disney behind it they expect practically all of the majors to join. So if you have media from non-participating studios, they might not appear.
You can log into Vudu, Amazon, and/or Google Play, and there's your media, as well as the Movies Anywhere channel itself.
Nvidia Shield, Roku Stick (3600), Ultra (4640), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.