Fast Motion
undercranking
Fast motion cinematography compresses screen duration so action plays faster than it occurred, by undercranking the camera or by retiming a normal-rate take. Crowds smear, clouds race, and labor can look absurdly efficient because too many events occupy too little time.
Narrative function
Use it when real time cannot hold the life in front of the lens: a factory that never stops, a city that should feel over-efficient, a chase whose danger is relentlessness rather than one punch. Subtle acceleration can be funnier or more oppressive than a cartoon speed-up.
Keep sound on its own clock. Pitch-shifted footsteps often betray the trick.
It is the wrong tool for weather, construction, or a night becoming morning. Those need interval sampling, not sped-up continuous action.
If the camera itself steps through space while hours collapse, you wanted a hyperlapse. Do not accelerate a performance whose contacts and gravity must stay honest.
How it works
Undercrank (shoot fewer frames per second than playback) or retime in the cut with a planned speed ratio. Longer exposure per frame, if the shutter stays open, increases motion blur.
Check hands, object contacts, and foot cadence after the speed change. Prompt: Undercranked fast motion of [Subject], crowds smearing, clouds racing, planned speed ratio, coherent contacts.
When to use it
Use it when a mailroom, assembly line, or crowd must feel over-efficient, as in a comic or cosmic crush of ordinary work. Do not use it to stand in for a day-to-night sky.
Compared with similar shots
Fast motion speeds continuous action. Time-Lapse samples the world at long intervals so slow change (shadows, crowds as systems) plays quickly.
Hyperlapse is time-lapse plus a camera that advances through space. Slow Motion is the inverse stretch.
A Speed Ramp changes rate inside one shot rather than holding a constant acceleration.
In film
Modern Times uses factory rhythm so mechanized work feels like a speeded machine wearing a man. A Clockwork Orange undercranks selected passages so appetite and violence become brisk, grotesque efficiency.
Mad Max: Fury Road alters cadence on chosen action beats rather than running the whole film as a cartoon. Koyaanisqatsi is often grouped here, but its urban crush is mostly interval time-lapse.
Modern Times 1936Factory rhythms exaggerate the pressure of mechanized work.
Mad Max: Fury Road 2015Selected action beats use altered motion cadence and speed.
Prompt it
State that time is compressed and what races. Still: a pose that implies acceleration (smeared extras, streaked traffic) while the subject, if they must stay readable, holds.
Video: Fast-motion view of [Subject] and the environment, time compressed, crowds and weather racing, coherent hands and footsteps, not a motionless sun over a smoking crowd.
What usually goes wrong
The usual wrong cousin is Time-Lapse. The tell is a racing crowd under a sun and shadows that never move, or people who teleport instead of stepping.
Fix: keep continuous action and a planned speed ratio, then check contacts. If hours must collapse, change to interval photography.
Questions
What is Fast Motion in film?
Fast motion is undercranked or retimed action that occupies less screen time than it took in the world, so movement looks accelerated.
Fast Motion vs Time-Lapse
Fast motion speeds a continuous take. Time-lapse captures frames at long intervals so processes too slow for real time (light, weather, crowds as flow) play in seconds.
When should I use Fast Motion?
When ordinary movement should feel over-efficient, comic, or relentless, and the action itself is still a continuous performance.
How do I prompt Fast Motion for AI image or video?
Write undercranked or accelerated playback, crowds and weather racing, and coherent contacts. Do not ask for hours of sun travel unless you actually want time-lapse.
Melies can generate this Fast Motion
Melies is the AI filmmaking workspace. This Fast Motion opens with the motion prompt loaded, so time is a setting you generate instead of a slider you guess.