Film - A Practical Guide to Video and Audio Compression - page 63

the video. If this is repeated for the next 2 frames as well, the fields and frames will come
back into sync. Over the course of 4 frames of film, 5 frames of video are created (or 10
fields of video). Figure 4-18 shows how these frames are mapped between the two kinds
of media.
This is called 3-2 pulldown but is more accurately described as 2-3 pulldown because
it better describes the input-to-output transformation.
The QuickTime software developed by Apple has tools built in to remove or add this
pulldown conversion. In fact, most compression tools on all platforms provide support for
this as well. Uniquely, the QuickTime platform provides it in a way that you can exploit
from within your own applications.
Because the pulldown is distributed evenly throughout the time base, the effect is
imperceptible until you push the pause button on a video recorder and you often see
frames on the TV screen that appear to contain a double image. This is only obvious when
there is some movement.
You also occasionally see this artifact when running video input cards in preview
mode or when you monitor an incoming DV stream via FireWire. That is just an artifact of
the monitoring stream, and when you play the ingested video back it looks fine.
Because the movie is running a little slower, the overall run time is a little longer.
Since the change is only 3%, it makes hardly any difference.

Frames Fields

A

Odd

Even

B

Odd

Even

C

Odd

Even

D Odd

Even

A Odd

Even

Figure 4-18 Film-to-video pulldown.