Although the video can't compare to standing beside or better yet behind you, even from the profile view the symptom is that your application of power is adrift as you begin the stroke then ends with a hammering kick
There is more than one reason for this but if I were debugging your cast I would start with these two things (1) rod taper and power mismatch with the line judging from the flex profile and (2) forward stroke path out of alignment with the top leg of the D-loop which I can't really see except when you re-set.
1) A gear mismatch can cause this because you can't really feel the load through the longer, slower motions requisite to long belly casting. A progressive flex from the lower portion of the blank (with ample power) is the preferred taper of most long belly casters myself included. You need enough grains to make that work, and the line looks under-gunned and/or the rod looks tippy.
So it's possible if not likely that as you start the forward stroke the rod has unloaded so you can't feel the d-loop as well, so you drift forward until you can and power late which causes the hammer-down.
So take pride in what you've got going thus far - in fact you set a gorgeous D-loop on most casts. To figure out if you can feel the start of the cast, look for the sliding fly at anchor and ask yourself if you feel the d-loop? If not, ask your buddies or a flyshop to try another line, rod or both.
3) Another common reason for the loss of power we're seeing is that your power stroke is out of alignment with the top leg of the D-loop when you come forward.
In other words, when you create that great D-loop of yours the top leg, what Rajeff calls "the javelin", is pointing opposite that stump. BUT when you come forward, the rod drives toward the big rock over there where you think there's a gnarly 15# native buck with shoulders.
If these two vectors aren't aligned, you will have a loss of power (i.e. dynamically create slack) and the symptom described above in bold is the compensation and we all know men compensate with power more often than grace.
Every time I've taught a couple the girl always casts better faster because she never thinks of power as the answer. Of course the better she casts, the more the guy compensates
In any case, you're very close and we're all looking forward to the video where you've got the rest of it nailed. Keep at it and good luck.