Performing a 3:2 Pull-Down
The most common approach to distributing film’s 24 fps among NTSC video’s 29.97 fps is to perform a 3:2 pull-down (also known as a 2:3:2:3 pull-down). If you alternate recording two fields of one film frame and then three fields of the next, the 24 frames in 1 second of film end up filling the 30 frames in 1 second of video.

As shown above, the 3:2 pattern (actually a 2:3:2:3 pattern since frame A is recorded to two fields followed by frame B recorded to three fields) repeats after four film frames. Virtually all high-end commercials, movies, and non-live television shows use this process prior to being broadcast.