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In practice the most important case is a lm camera speed
of 23.976 fps and a NTSC video assist.
This creates the situation described in the drawing.
From the rst lm frame, two video elds are derived, the
second lm frame, three video elds are derived, from the
next lm frame, two video elds and so on.
The Pull-Down information is created as follows:
Every time, the video eld corresponds to a new lm frame,
the letter will change either from A to B or B to A and the
number will be set to 1. As long as no new lm frame is
taken, the video elds are counted, beginning from 1.
Consequently A2 is the rst repetition of A1. B2 would be
the rst repetition of B1, B3 would be the second repetition.
In spite of the fact that the name Pull-Down comes from the
working practice in the NTSC systems, where on a telecine
the lm is running on 23.976 fps and gets converted to
29.97 fps, the denition of Pull-Down information on the
IVS can also be applied to PAL and to lm speeds other
than 23.976 fps.
Film
1
Film
2
Film
3
Film
4
A1 A2 B1 B2 B3 A1 A2 B1 B2 B3
Like all man readable information, the data is inserted as
a window on the monitor image. The window can be
switched on and off independently. Background, position
and character format can be altered without affecting the
settings of other windows.
Note: Pull-Down information is only inserted when
timecode is actually recorded on lm. If there is
no timecode recording, for example because
the camera is not running on a timecode speed,
only A1 will be displayed.
Video-Ait-Sytem