Massively Happy

This is a mystery puzzle in video form. By mystery puzzle, I mean a problem whose rules are to be self–inferred from the activity itself, and answer is (usually) in the form of a word, or short phrase. Mystery puzzles are typically “scored” on the basis of time you take to solve them; in this one, you can also choose to solve with less information, and use observation in lieu of logic, or vice versa. Please do not spoil the solution in the comments section.