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Re: Keycode number fields


The field sequence in a 3:2 pulldown is identified over a total of five
frames because that is how long it takes the sequence to repeat.  It is quite
important to have this information when cutting a negative to a video
workprint.  Also, some nonlinear editors, such as the Avid Film Composer,
depend on proper field sequence when digitizing, so it is very helpful in
that connection. 

A typical "A" frame sequence might be:

    Film frame A, field 1 (f1 of Video frame 1), usually displayed as A1
    Film frame A, field 2
    Film frame B, field 1 (f1 of Video frame 2)
    Film frame B, field 2
    Film frame B, field 3 (f1 of Video frame 3)
    Film frame C, field 1
    Film frame C, field 2 (f1 of Video frame 4)
    Film frame D, field 1
    Film frame D, field 2 (f1 of Video frame 5)
    Film frame D, field 3
....and so forth.

Note that it is possible, depending on the controller used, to have the
sequence start on "B," "C," or "D" frames as well.

The primary purpose of this in a film-to-tape suite is to verify that the
telecine, VTR(s), and controller are editing properly.  This is done
(typically) by punching a hole or making a mark at a specific point somewhere
near the beginning of a roll of film, setting that frame to be your "zero"
point, and then allowing the system to do an edit, recording the "burn-in" or
window on tape.  If all is well, the "zero" punch or mark should appear on
the first field of the first frame in the selected sequence when you jog the
tape on a field-by-field basis.

Hope this helps.

Christopher Bacon
DuArt Film & Video