• In motion pictures, television, and in computer video displays, the frame rate is the number of frames or images that are projected or displayed per second.
  • Frame rates are used in synchronizing audio and pictures, whether film, television, or video.
  • In motion pictures and television, the frame rates are standardized by the Society of Motion Picture and Television Editors (SMPTE). 
  • SMPTE Time Code frame rates of 24, 25 and 30 frames per second are common, each having uses in different portions of the industry. 
  • The professional frame rate for motion pictures is 24 frames per second and, for television, 30 frames per second (in the U.S.).
Image result for 24 frames

 Image result for 24 frames Animations
     Why 24 frames per second:
  • Initially we use the frame rate about 12 to 16. Fall believe your brain perceives a series of discrete images displayed one after the other. Illusion of motion works at 16 fps, it better works at higher frame rates. 
  • The higher the number of frames playing per second, the smoother the video playback appears to the user. 
  • Film uses 24 frames per second to allow the viewer to perceive smooth playback.
  • 24fps is just the standard with sound without sound films.
  • Due to high cost of film, most silent films are built at 16-18 fps and projection may be close to 20-24 fps.
    Silent films:
  • Early silent films had stated frame rates anywhere from 16 to 24 frames per second (fps), but since the cameras were hand-cranked, the rate often changed during the scene to fit the mood.
  • Projectionists could also change the frame rate in the theater by adjusting a rheostat controlling the voltage powering the film-carrying mechanism in the projector.
  • In the mid to late 1920s, the frame rate for silent films increased to between 20 and 26 fps.
     Sound films:
  • When sound film was introduced in 1926, variations in film speed were no longer tolerated, as the human ear is more sensitive to changes in audio frequency. 
  • Many theaters had shown silent films at 22 to 26 fps which is why the industry chose 24 fps for sound as a compromise.
  • From 1927 to 1930, as various studios updated equipment, the rate of 24 fps became standard for 35 mm sound film. 
  • At 24 fps the film travels through the projector at a rate of 456 millimetres (18.0 in) per second.
     Animation:
  • In drawn animation, moving characters are often shot "on twos", that is to say, one drawing is shown for every two frames of film which usually runs at 24 frames per second, meaning there are only 12 drawings per second.
  • Even though the image update rate is low, the fluidity is satisfactory for most subjects. However, when a character is required to perform a quick movement, it is usually necessary to revert to animating "on ones", as "twos" are too slow to convey the motion adequately.
  • Animation for most cartoons is produced as cheaply as possible, and is most often shot on "threes", or even "fours", i.e. three or four frames per drawing. This translates to only 8 or 6 drawings per second