24p 2-3 pulldown

When a video is shot in 24 frames per second (fps), in order to convert it to normal NTSC frame rate, the video is converted using a 3:2 pulldown.

A frame of NTSC video consists of 2 fields interlaced. These two fields add up to one frame, but are displayed 1/60 second apart. The odd lines of the frame are displayed first and then the even lines are displayed. The human eye merges these two fields into a single frame. However, if you pause the video/DVD, you can often see interlace artifacts in areas where something is moving. These artifacts look like a comb, where every other line is displaced from the lines around it.

What this means is that every odd frame of the 24 fps is copied to 3 fields in the video, and then every even frame is copied to the next 2 fields. In a best-case scenario, what you will see is 3 normal frames and then the fourth frame will be duplicated. in a worse case scenario, only every fourth frame will be clear, the rest will be some combination of two different frames.

24 fps to 30 fps (60i) translation
NTSC Frame Non-Blend translation Frame Blend Translation
0 0 0/0
1 0 0/1
2 1 1/2
3 2 2/2
4 3 3/3
5 4 4/4
6 4 4/5
7 5 5/6
8 6 6/6
9 7 7/7
10 8 8/8
11 8 8/9

As you can see, the non-frame causes a stutter every four frames (or eight times a second) and the frame-blending method causes two frames to be blurry followed by three frames not blurry. FinalCut Pro manual information on Working with 24p is very usefu.