In /Resources/Private/Templates/GridElements/Parallax.html the parallax-video uses the data attribute data-jarallax-video for the video-url.
This is enough to trigger jarallax and thus the javascript that deals with the configuration of parallax-video-classes in /felayout_t3kit/dev/js/main/contentElements/parallax.js
is being ignored (from my testing).
I suggest that we either change it so (1) all jarallax "items" are triggered from javascript or (2) that we add the other data-parameters into the HTML-template. The first suggestion is probably the safer one.