LESSON 83
Frame rates: 24, 25 and 30
Why three numbers rule moving pictures.
IN THIS LESSON
- What a frame rate is
- Why cinema settled on 24
- Why television chose 25 and 30
- Moving between rates
- Practice: picking a rate
What a frame rate is
A frame rate is simply how many separate pictures are captured or shown each second, written as frames per second or fps. Our eyes can pick out roughly ten to twelve images a second as separate pictures; above that, a run of still images starts to read as motion. So a frame rate is not about smoothness alone. It sets how motion feels, how much light each frame can gather, and which screens will play your footage without trouble. Choosing it is one of the first decisions on any shoot, because changing it later almost always costs something: speed, sound pitch or a stutter.
Why cinema settled on 24
Silent films ran anywhere from 16 to 24 frames a second, often cranked by hand and sped up or slowed down by the projectionist. When sound arrived in the late 1920s, speed had to stay fixed, because the ear notices a change of pitch far more readily than the eye notices a change of pace. Many cinemas were already showing films at 22 to 26 frames, so 24 was chosen as a middle value, and between 1927 and 1930 it became the standard for 35 mm sound film. Projectors flash each frame two or three times, so the screen flickers at 48 or 72 times a second while the story still runs at 24.
Why television chose 25 and 30
Analogue television took its timing from the mains electricity, which is very stable. Most of the world runs its grid at 50 hertz, so broadcast pictures there were built around 50 fields or 25 full frames a second. North America, Japan, South Korea and a few other countries use 60 hertz, which led to 30 frames. When colour arrived, the 60 figure was lowered by 0.1 percent to avoid a picture fault called dot crawl, which is why you still see odd numbers such as 29.97 and 59.94 on cameras today. The same 1.001 divisor gives 23.976 for film-rate work in those regions.
Moving between rates
Footage shot at 24 can be shown at 25 by speeding it up by about 4 percent. Picture motion looks normal, and the sound rises by a little under a semitone, which most viewers never notice; some studios shift the pitch back. Going from 24 to a 60-based system is harder, because frames must be repeated in an uneven pattern, and that can add a small stutter. This is why it pays to know where the film will be shown before you press record.
Practice: picking a rate
This part is working practice, not a rule. If your work will live on cinema screens or has a filmic brief, 24 or 23.976 is the usual choice. If it is for broadcast or the web in a 50 hertz country, 25 keeps lights from flickering and matches local television. In a 60 hertz country, 30 or 29.97 does the same. Pick one rate for the whole project, set every camera to it, and write it on the first page of your notes.
| Rate | Where it comes from | Typical use |
|---|---|---|
| 24 / 23.976 | Sound film standard, 1927 to 1930 | Cinema, filmic drama |
| 25 | 50 hertz mains, most of the world | Broadcast and web in those regions |
| 29.97 / 30 | 60 hertz mains, lowered 0.1 percent for colour | Broadcast and web in North America and Japan |
| 50 / 59.94 | Full field rate of the same systems | Sport, fast motion, slow-motion source |
Try it today
- 01Find out the mains frequency where you live: 50 or 60 hertz.
- 02Record ten seconds of a person walking at 24, at 25 and at 30 fps.
- 03Put all three clips on one timeline set to 25 fps and watch the motion.
- 04Note which clip looks most like cinema to you, and why.
- 05Set your camera's default to the rate that suits your next project.