SMPTE Timecode Calculator

SMPTE timecode counts frames as HH:MM:SS:FF. At an exact integer frame rate (24, 25, or 30fps), that count matches real elapsed time exactly. NTSC video, though, actually runs at 30÷1.001 (≈29.97) or 60÷1.001 (≈59.94) fps — not the round 30/60 the timecode digits count in — so the raw HH:MM:SS:FF numbers drift behind real-world elapsed time by about 3.6 seconds per hour at 29.97fps if left uncorrected. Verified via web search against Wikipedia's SMPTE timecode reference rather than relied on from memory.

Drop-frame notation (DF) fixes this by skipping the frame numbers 0 and 1 (0-3 at 59.94fps) at the start of every minute except every tenth minute, which removes almost exactly the right count of frame numbers to keep the displayed timecode in sync with the wall clock — no video frames are ever actually dropped, only some of the numbers used to label them. This reproduces the standard reference example that a drop-frame count at 29.97fps advances directly from 01:22:59:29 to 01:23:00:02 (skipping the labels 01:23:00:00 and 01:23:00:01), and that exactly 108 frame numbers are dropped over a full drop-frame hour (108,000 nominal 30fps frames minus 108 dropped = the well-known 107,892 real frames per hour at 29.97fps).

The result shows the drop-frame-corrected total frame count, the real elapsed duration computed from the true (non-round) frame rate, and — for comparison — the 'literal' duration you'd get by naively reading the HH:MM:SS:FF digits as if the frame rate were an exact round number. The difference between those two is the drift that drop-frame notation exists to correct.