VITC
Vertical interval timecode (VITC, pronounced "vitsee" or sometimes "vits") is a form of SMPTE timecode embedded as black-and-white bars in a pair of the normally unseen vertical interval lines in a television signal. There can be more than one VITC pair in a single frame of video: this can be used to encode extra data that will not fit in a standard timecode frame.
VITC contains the 64 data bits of the SMPTE linear timecode frame embedded in a new frame structure with extra synchronization bits and an error-detection checksum. The VITC code is always repeated on two adjacent video lines, one in each field. This internal redundancy is exploited by VITC readers, in addition to the standard timecode "flywheel" algorithm.
A video frame may if necessary contain more than one VITC code, recorded on different line-pairs. This is often used in production, where different entities may want to encode different sets of time-code metadata on the same tape.
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