Apple Final Cut Pro 7 - Manual (Page 1932)

24 Versus 23.98 fps
Although the term 24p implies 24 frames per second, the value 24 is usually inaccurate,
because most people working within NTSC standards actually shoot at a frame rate of
23.976 fps (commonly referred to as 23.98 fps). On the other hand, 24 fps footage
transferred to PAL, as well as most film, is recorded at exactly 24 fps.
Although it may be easier to say “24p,” keep in mind that in some cases, such as during
audio post-production, it’s critical to state the exact frame rate of your footage.
Telecine, Pull-Down, and Reverse Telecine
The following sections describe methods for embedding and extracting 24p video in
different formats. Some of these techniques are based on existing film-to-video methods,
and some are newer approaches. The basic technique for transferring film to video, called
telecine, uses a process called pull-down to map 23.98 fps film to 29.97 fps interlaced
video. Once the video is captured on disk, software can perform reverse telecine, or
reverse pull-down, to restore the original 23.98 fps film frame rate.
In progressive digital video systems such as 720p60 DVCPRO HD video, a similar process
can be performed in-camera to map 23.98 fps to 59.94 fps, but entire frames are duplicated
instead of fields. During or after capture, the duplicate frames are removed. A camcorder
or deck that performs duplicate frame insertion can add metadata (known as flags) that
inform software when to remove or ignore duplicate frames.
Note: Pull-down refers to the addition or removal of fields, not duplicate frames.
Standard 3:2 Pull-Down
Also known as 2:3:2:3 pull-down, this is the standard telecine method of transferring film
to NTSC video. The film is slowed by 0.1 percent (a factor of 1000/1001) from 24 fps to
23.98 fps, and then each film frame is transferred to interlaced video in a repeating 2:3:2:3
field pattern.
1932 Appendix D Working with 24p Video