How to calculate timecode
SMPTE timecode gives every frame an address: hours, minutes, seconds and frames, written HH:MM:SS:FF. The last field counts frames within the second, so it rolls over at the frame rate: after 00:00:00:23 at 24 fps comes 00:00:01:00. That's why you can't add timecode like ordinary numbers. The calculator turns each timecode into a frame count, does the arithmetic, and turns the answer back into timecode.
Drop-frame and non-drop-frame
NTSC rates (23.976, 29.97, 59.94) run 0.1% slower than their round numbers. Counting 30 frames a second at 29.97 makes timecode fall behind the clock by about 3.6 seconds an hour. Drop-frame timecode keeps it honest by skipping frame numbers 00 and 01 at the start of every minute, except minutes divisible by ten. No frames of picture are lost; only labels are skipped. Drop-frame is written with a semicolon before the frames (00:01:00;02) and only exists at 29.97 and 59.94. Broadcast usually wants it; film and online work usually use non-drop.
Common jobs
- Total running time: add each scene's or reel's duration in "Add and subtract".
- Shot length: put the In and Out points into "Duration between two timecodes".
- Delivering at another rate: a 24 fps film delivered at 25 fps keeps its running time when conformed, or runs 4% fast with the classic PAL speed-up.
- Slow motion: shoot at 48, 60 or 120 fps and play on a 24 fps timeline for 50%, 40% or 20% speed.
Where to go next
The course lessons Assembly and rough cut and Pacing, rhythm and grade cover cutting to time. Estimate the length of a film before you shoot it with the script runtime calculator, and the size of the export with the file size calculator.