This is the 'Mobius Trailer' released in 2013 for Metro: Last Light. The game itself was also released in 2013 and has a post-apocalyptic setting, and the trailer matches your description of the action pretty much perfectly:
The important thing is that the video is a long tracking shot in a motionless world, all characters are frozen in time.
The trailer is one long tracking shot showing various scenes of a metro station, with audio cues to imply action but only the camera itself is moving.
The camera starts in a kind of bunker with a military officer reaching for a button which seems to close the huge bunker door, seemingly leaving countless civilians stranded outside, at the mercy of the monsters.
The trailer starts zoomed-in on the eye of a man in a dirty military-style uniform, hand on a lever with a horde of monsters behind him. The camera then pans to show what he is looking at instead of the monsters: a child reaching out to him from behind a large closing door.
The tracking shot shows their distress (particularly some children), visits some living quarters and grim corridors with people fighting the monsters (civilians, maybe soldiers too)...
The camera shows various grisly scenes in the metro station: soldiers defending a subway car converted into a hospital, civilians inside a kitchen using ad-hoc weapons (boiling water, a cleaver, etc.), more scenes of military-grade weapons being used against another horde, a man trying to hold a monster who's moving towards a crib, a woman protecting two children with a torch, a soldier holding live grenades while monsters swarm him, and so on.
... then comes back to the initial bunker and reveals that a swarm of monsters is inside, meaning that the military is actually sacrificing himself to lock the monsters in, maybe also setting off a bomb to destroy them inside the bunker.
Not quite, but close. The final scenes show a large group of much more professional looking solders arriving from the subway tunnel near where the door is closing. Then, it pans back to the eye of the original man where the trailer started.
Given the rest of the scenes, I think it's implied that he's closing the door to prevent a swarm of monsters from attacking the professional soldiers who just arrived, sacrificing himself so the new arrivals can get to the people already under attack in time.
The (age-restricted) trailer on YouTube:
