Drop-Frame and Non-Drop-Frame Timecode

Although the timebase of NTSC video is a constant 29.97 fps, SMPTE timecode counts it in two different ways: drop-frame and non-drop-frame.

Non-Drop-Frame Timecode— Even though the true timebase of NTSC video is 29.97, non-drop-frame (NDF) timecode counts 30 fps. Over time, however, the discrepancy results in a small but significant difference between the duration indicated by the timecode and the actual elapsed time (Figure 18.3). Nevertheless, NDF timecode is easy to understand and usually is used for source tapes. Video equipment displays NDF timecode with colons between the numbers.