Drop-frame skips labels, never pictures
29.97 DF uses 30 nominal labels/second, skipping ;00 and ;01 at the start of each minute except every tenth minute. 59.94 DF uses 60 nominal labels/second and skips ;00 through ;03 by the same rule. Frames = nominal label count − d × (total minutes − floor(total minutes ÷ 10)), where d is 2 or 4.
Worked example
At 29.97 DF, 00:01:00;00 and 00:01:00;01 do not exist; 00:01:00;02 is frame 1,800 (30 × 60 + 2 − 2). 00:10:00;00 is frame 17,982 (18,000 − 18). 01:00:00;00 is frame 107,892 (108,000 − 108). At 59.94 DF the corresponding values are ;04 / 3,600, 35,964 and 215,784 frames.
Assumptions and limits
DF is valid here only for 30,000/1,001 and 60,000/1,001 fps. The semicolon identifies DF; a colon is also accepted with a DF rate and normalized on output. 23.976 has no DF mode here. DF approximates wall time: a 29.97 DF hour is 3,599.9964 actual seconds, not exactly 3,600.
For supported rates and input formats, see the frame-rate reference on the calculator home page.