Your video shows exactly what I said.
1. Slide is racked and round is chambered
1a. Slide moves to the rear, ejecting spent casing (if present) and allowing the next cartridge to move into the action.
1b. On the forward stroke of the slide, the round is pulled from the feed lips of the magazine and pushed up the feed ramp into the chamber and the striker is locked back, into the firing position
2. Trigger pull
2a. Finger is placed on the trigger, operating trigger block safety
2b. Trigger pulled, just before sear disengagement firing pin safety is moved clear of the path of the striker/firing pin, sear is disengaged, which drops striker/firing pin
3. Round fires
3a. Striker impacts primer, causing it to fire
3b. Primer ignites powder, which drives the bullet from the casing and down the barrel
3c. Recoil force from powder explosion drives slide backward, starting Step 1 again.
If the glock were DA, there would be no need for the passive firing pin block safety.