Digital Video Frame Rates

Frame rate refers to how many images per second are displayed by the respective video file (or how many times per second the video image is 'refreshed'). It is abbreviated FPS (frames per second). IT IS NOT THE SAME AS SHUTTER SPEED. (Follow this link for a 5 minute video which demonstrates the difference between the two)

You can think of the frame rate as how many times per second you 'sample' time. The higher the frame rate, the higher the 'temporal resolution' of your video is, or the closer to 'live' the image will appear. There is a limit to this, however: the human brain is only capable of 'refreshing' the input from the optic nerve between 60-70 times per second, so we can't discern frame rates higher than this. (Look here for some clever visual tricks exploiting video and human perception, including how to make liquid water 'freeze' in mid-air.)

There is a frame rate for capturing the image (camera/recording framerate) and a framerate for playback.

Recording framerate = playback framerate : movement is natural, realtime speed

Recording framerate > playback framerate : (i.e. recorded at 60 FPS, played back at 30 fps) movement is in slow motion

Recording framerate < playback framerate : (i.e. recorded at 24 fps, played back at 48 fps) movement is in fast motion

The basic frame rate of celluloid film is 24 fps.

DIGITAL VIDEO FRAME RATES

First of all, video can be displayed in both frames and fields - see Interlace and Progressive. These are usually written as i or P, such as 1080i or 1080P to distinguish HD video using either fields (i) or frames (P). A field is, in essence, only half of a video image, so two fields = one frame.

Next, digital video can effectively be recorded and/or played back at virtually any frame rate, but there are accepted standards, mainly:

23.98 (often written as '24')

29.97 (often written as '30')

59.94 (often written as '60i')

23.98 vs 24 FPS/ 29.97 vs 30 FPS

While you can make digital video in any of these frame rates, nearly all electronics-based distribution (web, TV, broadcast) will use the fractional figure, 23.98/29.97 as opposed to 24/30. (This is because the electronic transmission of video uses up the few hundredths of a second for a momentary electronic pulse to send along color info - prior to NTSC standardization, black and white video could be a round 30 FPS, but the advent of color introduced the decimal numbers). As of this writing, the only general contemporary use for round-number frame rates is in the DCP format, used in digital theatrical projection.

BEST PRACTICES

Conversion from 23.98 to 24 or 29.97 to 30 FPS for DCP creation is generally easy and artifact-free, so if a project is begun in the electronic format converting is not problematic.

The most important rule is stick with one frame rate throughout your project. Mixing frame rates can complicate audio sync and editing. If you have mixed recording frame rates (for example from multiple sources), conform them all to a single overarching project frame rate that matches your desired final framerate.