Seconds to HH:MM:SS

An API, a player or a stopwatch hands you 3725.5 seconds and you need it in another shape: 01:02:05 for a caption, 01:02:05.500 for a cut in the editor, or 1.034861 h for a timesheet. Type the total in the field and all three readings appear at once, updating on every keystroke, with no dividing by 3600 by hand and no rounding slip on the way.

The classic mix-up is treating decimal hours and HH:MM as the same notation. An hour and a half is 1.5 h, not 1.30 h, and someone who writes 1.30 on a timesheet has just claimed 1 h 18 min. Second thing: the hours field does not wrap at 24. A hundred thousand seconds reads 27:46:40, which is correct for a duration and would be wrong if you expected a clock time.

The field takes decimals and negatives, with the sign placed in front of the result. Seconds are truncated in the HH:MM:SS reading and the fraction moves into the milliseconds. One quirk worth knowing: when the fraction sits very close to a full second, the milliseconds field can show 1000 instead of rolling the second over, and in that case the decimal-hours reading is the one to trust. Nothing leaves your browser.