Slow Motion Calculator (Frame Rate, Playback Speed & Clip Length)

How it works

slow-motion factor = recording fps ÷ playback fps · playback speed = playback fps ÷ recording fps × 100% · timeline length = real length × factor · frames = recording fps × real length · 180° shutter = 1 ÷ (2 × recording fps)

Slow motion comes from overcranking: recording more frames per second than the timeline plays back. Every frame is shown, just spread out, so 120 fps conformed to a 24 fps timeline plays at 20% speed — five times slower — without the stutter of software-stretched footage. For natural motion blur use the 180° shutter rule at the recording frame rate (1/240 s at 120 fps), which also needs more light. If you record slower than the timeline (undercranking) the factor is below 1 and the action speeds up.

Worked example

Ten seconds of action recorded at 120 fps and played on a 24 fps timeline is slowed 5.00× to 20.0% speed and lasts 50.00 s. That is 1,200 frames, shot at 1/240 s for the 180° rule.

Sources: Wikipedia — Slow motion · Wikipedia — Rotary disc shutter (180° rule)

Frequently asked questions