Apple Compressor 2 - Manual (Page 133)

Chapter 10 Creating MPEG-2 Output Files 133
About 24p (23.98p)
For DVD authoring and encoding, 24p refers to a video sequence that contains 24
progressive (non-interlaced) frames per second, with NTSC-related standard definition
frame dimensions (720 x 480 for MPEG-2). Film-based movies have a native frame rate
of 24 fps, and because the MPEG-2 format is able to represent 24 fps video internally,
many commercial movie DVDs are encoded in this way. But any time you use NTSC
video in your project, the frame rate of film-transferred material will be slowed down
from 24 fps to 23.976 fps (rounded to 23.98) and a 2:3:2:3. pull-down is added. So, the
more accurate term is actually “23.98p.”
Compressor can also do this for 24P source video files. For such material, the 23.98
frame rate option (in the Video Format tab) compresses each source frame one-for-one,
without compressing repeated frames or fields in order to achieve a 29.97 fps display
rate. This results in higher quality at a lower compressed bit rate than would be possible
if the 24p material were converted to 29.97 fps prior to transcoding. Compressor also
sets internal MPEG-2 frame flags correctly, so DVD players will properly apply the 3:2
pull-down process for display on 29.97 fps interlaced NTSC TV sets.
This capability is supported in the Apple end-to-end 24p (23.98p) editing and delivery
solution (Final Cut Pro with Cinema Tools). The workflow typically goes like this:
23.98 fps film > Telecine > 29.97 fps video > Final Cut Pro > Cinema Tools > 23.98 fps
video > Compressor > DVD Studio Pro
Note: If your source video has a frame rate of 24.00 fps rather than 23.98 fps,
Compressor skips one out of every 1000 source frames. If the 24p source video is
23.98 fps, Compressor transcodes all source frames, without skipping (or repeating)
any of them.