That horrendous tape is a lesson in many ways.
The tail rotor is probably hit (collision?) off camera. This leads to the loss of the tail section just ahead of the vertical pylon, most likely caused by the imbalance of the loss of a tail blade, and the ensuning structural loads at the "weak point".
This antitorque failure results in spinning about the mast, and then wild cyclic excursions as the pilot is unable to maintian orientation. One can speculate that if the collective had been dumped then, fast, the spinning might have stopped and some kind of controlled low-power (zero power) descent could have been arranged. But that is asking alot.
Note that the bucking of the fuselage as the spinning occurs leads to blade-fuselage contact. The bucking is because the rotation of the fuselage exposes different sections of the rotor to the relative wind, so that the "back flap" affects the rotor sequentially as the fuselage turns. If the crew is not able to know where the wind is coming from, they cannot keep the fuselage level. This pitching and rolling eventually leads to large flapping events and blade to fuselage contact. The broken blades are uneven in length, so there are large cyclic imbalances that help tear the helo apart.
I believe the helos are Mi-2's which are 1st gen machines with relatively weak structures (or very light structures, depending on viewpoint.)
The tearing apart ruptures the fuel cells, which spray avgas everywhere, especially onto the running engine, which ignites same.
Not at all a pretty picture.