Vincent,
Thanks so much for your efforts, (and the rest of the ZP crew that are helping).
If you need any help testing just shoot me an email. I have everything running locally on Xampp so I can test easily.
I've been following along, because of my interest. I'm hoping your coding for handling YouTube video?
I have hosted my own mp4's on my shared server in the past and the playback is always terrible. That's why I switched to Youtube which is very robust and it's free.
You can create playlists in your YouTube account, and if you use the proper embed code, your playlist is available in a popup menu on the screen.

BTW I really like the zpBootstrap theme. Works so well on all devices.
Seems like Fancybox & Bootstrap are both adaptable for YouTube vids, but I don't understand coding, so I am no help.
http://fancyapps.com/fancybox/3/docs/#video
https://getbootstrap.com/docs/4.1/utilities/embed/