A time-lapse is a video built from still photos taken at a fixed interval over an extended period, played back in sequence to compress hours of real time into a short clip.
A time-lapse compresses hours into seconds by shooting stills at a fixed interval and playing them back at video speed, showing motion too slow to notice in real time: shadows crossing a plaza, a tide coming in, storm clouds building. Whether it looks smooth or stuttery comes down almost entirely to the interval between frames.
Slow subjects like a sunset want a longer interval, around 3 to 5 seconds; fast subjects like low clouds on a windy day need 1 to 2 seconds or the motion jumps between frames. Getting the interval wrong is costly because there is rarely a second chance at that particular light, and 400 frames shot at the wrong spacing cannot be fixed afterward. Total runtime is a straightforward calculation from interval, clip length and frame rate, which is what a time-lapse planner works out before the first frame.
A photographer wants a 20-second time-lapse clip of a sunset for 30fps video, which means 600 frames. Shooting from an hour before sunset to twenty minutes after gives an 80-minute window, so the interval is 80 minutes divided by 600 frames, about 8 seconds. That suits the slow colour change in the sky, but if fast low clouds move through, 8 seconds between frames makes them jump across the frame in visible steps rather than gliding.
Cutting the interval to 3 seconds fixes the clouds but now produces 1,600 frames over the same window, a 53-second clip. The other fix is to keep the 8-second interval but tighten the shoot to a 40-minute window around the best light, ending up with 300 frames and a 10-second clip. Manual exposure and a fixed white balance are locked before the first frame, or the finished clip flickers as the camera re-meters every shot.
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