Drop-frame drops no frames.

Not one frame of picture is ever discarded. Drop-frame is a renaming scheme: it skips two labels at the top of every minute except every tenth, so the labels keep up with a clock the nominal rate does not. A timecode counts at 30 while the pictures arrive at 30000/1001, so a non-drop hour of labels takes 3603.6 real seconds — 3.6 seconds slow every hour and 86.4 seconds every day. And drop-frame overshoots: ten minutes of its labels is 599.9994 real seconds, so it ends up about 86 milliseconds fast per day. It is not exact either, and this page will tell you by how much.

The engine is free and needs no account. Write the rate and the marks, and every label comes back as the frame number it names — with the duration computed from those frame numbers, never from the digits, because you cannot subtract timecodes: 00:00:59;29 to 00:01:00;02 reads as three frames and is one. It catches labels that were never issued, and it reads the separator as what it is — a semicolon is drop-frame, a colon is non-drop, and the same eight digits name two frames 108 apart. Every lane ships a worked example that costs nothing. Writing the report needs credits.