This is a VERY interesting and important video and it's about something that was never discussed before.
I already did some exercises on my own; since I've read (or listened? don't remember) this nice tip on the curriculum!
What I usually do is to practice passages from a fingering to another (for example from D to F) trying to be less sloppy as possible and caring that all the fingers involved are lifted or reach the body of the instruments
toegether. If you tongue every note is easy to cover a sloppy fingering when the fingers involved go into the right position in a few milliseconds of distance each other.
But, if you're playing legato those notes, there's no escape! You
will hear any imperfection if your movement is not accurate as a surgeon. So those exercises helps a lot. Definitely.
And now, too, I have a question.

I tried the roll on G exercise on the warmstone ocarina I wear.
And, I just can't keep the ocarina steady with one hand like Karl does in a certain passage. I detail this:
If I try to keep the ocarina only with third and fourth finger and the thumb (counting from the thumb = 1) it slips, moving towards the bottom part of the instrument. There ARE moments in which, to show the exercise, Karl just keep the ocarina with those fingers easily and steadily.
Of course during the roll you have to be fast so there's no time for the instrument to move, but in the beginning when you learn you have to practice slow as you know and I find that precise exercise to be unpractical, if the instrument it's not in your mouth.
Of course if the ocarina is between my lips too there's an extra point of contact between me and the ocarina so the instrument remains balanced and I can practice the exercise slowly as necessary.
Thank you for reading!
I hope it's clear.