Drop-frame 29.97 drop-frame timecode, NTSC DF, NDF 

Drop-frame timecode refers to a method of counting timecode in 29.97 fps video.
It does not refer to actual frames of video being dropped that would affect video quality. Since 29.97 fps is not exactly 30 fps, when counting in drop-frame certain numbers in the timecode counter are skipped in order to ensure that the timecode will reflect the real-time length of the program. The counterpart of drop-frame is non-drop which does not skip numbers when counting timecode. To prevent drift, it is important to time-stamp in the correct mode

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