Inser ter facilities – ARRI 535B User Manual
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All video assists are based either on PAL or NTSC video
systems, with a fixed video frequency of either 25 full video
frames per second with PAL or 29.97 full video frames per
second with NTSC. The speed of the film camera however
can be selected over a wide range. At every film speed
which is different from the video frequency, the IVS has to
add repeated video fields to compensate for the different
frame rates.
In practice the most important case is a film camera speed
of 23.976 fps and an NTSC video assist.
This creates the situation described in the drawing.
From the first film frame two video fields are derived,
from the second film frame three video fields, are derived,
from the next film frame, two video fields and so on.
The White-Line flag works as follows:
Every time the video field corresponds to a new film 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 film frame is
taken, the video fields are counted, beginning from 1.
Consequently A2 is the first repetition of A1. B2 would be
the first repetition of B1, B3 would be the second repetition.
On every A1 or B1, the selected video line will be set to
video signal white, indicating that only these video frames
correlate one-to-one to film frames. The duplicated video
fields are not marked.
In spite of the fact that the name Pull-Down comes from the
working practice in the NTSC systems, where on a telecine
the film is running on 23.976 fps and gets converted to
29.97 fps, the definition of Pull-Down information on the
IVS can also be applied to PAL and to film speeds other
than 23.976 fps.
Note:
The insertion of White-Line flags is only done
when time code is actually recorded on film. If
there is no time code recording, for example
because the camera is not running on a time
code speed, no White-Line flag is sent out.
Note:
The White Line has priority over VITC lines. If
the same line is selected for White Line as well
as for VITC, White Line will appear.
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