Apple Final Cut Express HD - Manual (Page 1055)

Appendix B Frame Rate and Timecode 1055
XIII
Drop frame timecode was invented to compensate for the discrepancy between 29.97
and 30 fps. Every minute except each tenth minute, two timecode numbers are
dropped from the timecode count. This drop frame mode of 30 fps timecode remains
accurate compared to the actual time passed, with a strange side effect that two
numbers each minute vanish from the count.
Timecode on Tape
There are several kinds of timecode recorded on videotape, each stored in a different
part of the video signal. LTC timecode is stored as an audio signal, while VITC is stored
in a line of each video frame.
 LTC (longitudinal timecode) is typically recorded as an audio signal on a dedicated
timecode track. You can add or change LTC timecode on your original tapes even
after they’ve been recorded because it’s recorded on its own independent track. LTC
is also used with professional audio formats, such as DAT and other multitrack audio
recorders. Because LTC is audio, it can be interpreted by a timecode reader even
when the tape is fast-forwarding, but it can’t be read when the tape is paused or
moving extremely slowly.
 VITC (vertical interval timecode) is recorded as part of the video signal, using several
video lines that are normally masked by consumer televisions. You can see VITC as a
series of white dots at the top of the video frame if you view the video on a
professional monitor in underscan mode. Because VITC timecode is part of the video
signal, it can only be changed on your original tapes if you also replace the video
itself, which is rarely worthwhile. The VITC part of the video signal is not captured as
part of a Final Cut Express HD clip’s video frame, but the VITC timecode can be
captured directly from the device control connection. Because VITC is part of the
video signal, which most decks can show in slow motion or even pause, VITC can be
read at very slow speeds, but it breaks up when fast-forwarding or rewinding.
The Difference Between Frame Rate and Timecode
The frame rate of your film or video describes how rapidly frames are photographed
or played back. It refers to physical speed of image capture and play back. Timecode
is merely a method of labeling frames with unique identifiers to easily find them
again later. It is a convenient way of giving each frame a name that can be referred to
later without having to verbally describe and visually search for it. Even though frame
rate and timecode are independent, people commonly confuse the two, which can
lead to frustrating problems in post-production. Before you start a project, be certain
that you understand the difference between these two terms.