What Is Frame Rate?

Think of a motion picture camera as a relentless still camera, taking many still photographs every second. Movies create the illusion of motion by showing still images in rapid succession. The number of images photographed per second is referred to as the frame rate of the movie and is measured in frames per second (fps). Frame rate describes both the speed of recording and the speed of playback. The more frames recorded per second, the more accurately motion is documented onto the recording medium.

Recording and playback speed are usually the same, though they do not have to be. For example, if you film a rubber ball bouncing on a sidewalk at 24 frames per second, your movie will have 24 unique photographs of the position of the ball. However, if you film at 100 frames per second, there are nearly four times as many photographs of the ball’s position during the same period of time. The more frames per second, the more precisely the exact position of the ball is documented.

Note: If you play back frames at a speed different from the original recording speed, you can create temporal effects such as time lapse and slow motion.

Early television systems selected frame rates based on local electrical standards to avoid electrical interference with the picture. NTSC in North America uses 30 fps (now adjusted to 29.97 fps for color NTSC) based on 60 Hz electrical power. PAL, used primarily in Europe, uses 25 fps based on 50 Hz electrical mains.

Because film cameras are relatively simple compared to video cameras, they allow shooting and playing back with a wide range of frame rates (although the standard projection speed is 24 fps). Video formats are much less flexible, partly because of their electronic complexity and partly because a television is designed to play video at only one frame rate. However, as video technology evolves, many digital camcorders now offer several frame rate choices while maintaining compatibility with existing NTSC and PAL video systems.

Figure. Diagram comparing the frames in 1 second of 60 fps footage to the frames in 1 second of 24 fps footage.