unlimited use of finesse

That animation is not Finesse that is Last Stand that you have also equipped. When Finesse is used your character does vault by putting hands on the window and throwing the legs straight through the window. When using Last Stand your character puts its hands on the window but keeps legs tucked in behind and then turning them forward when going through the window. Your video shows your character doing the latter so its not infinite Finesse but Last Stand being active. Its basically a knee attack that causes the stun to the killer. The animation plays on every vault until you successfully cause stun to the killer and turn off the perk.