You can use videos hosted Youtube and Vimeo in your course, but they need to be set up in a certain way to work in Xperiencify.
Option 1 is to set your video to completely public. Most course creators don't want to do this however as it makes your valuable videos discoverable online.
Option 2 is to set your videos to "Unlisted".
In Vimeo, here's the correct setting to use:
Your video link will be in a format like this: https://vimeo.com/295265678/8482f1684c
In Youtube, here's the correct setting to use: