Vertical Interval TimeCode (VITC, pronounced "vitsee") is a form of SMPTE timecode embedded as a pair of black-and-white bars in a video signal. These lines are typically inserted into the vertical blanking interval of the video 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 contain more than one VITC code if necessary, 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.
As a practical matter, VITC can be more 'frame-accurate' than Linear timecode (LTC), particularly at very slow tape speeds on analog formats. LTC readers can lose track of code at slow jog speeds whereas VITC can be read frame-by-frame if need be. At high speeds (FF/REW), the VITC is often unreadable due to image distortions, so the LTC is often used instead. Some VCRs have an auto selection between the two formats to provide the highest accuracy.
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