How to Slow Down a Video on iPhone

The fastest way to slow down a video on iPhone is to check how it was filmed first: a Slo-mo clip adjusts directly in Photos, while a normal clip needs iMovie's Speed slider instead. Here's both paths, and why one looks smoother than the other.

Slow down a video on iPhone shot in Slo-mo

If the clip was recorded in Slo-mo mode, open it in Photos and drag the white vertical bars below the frame viewer. Those bars mark exactly where the slow-motion section begins and ends. Everything outside them plays at normal speed, so a single Slo-mo clip can hold a fast lead-in, a slowed middle section, and a normal-speed ending, all adjustable after the fact without re-shooting.

This matters most for footage with fast, small movement. A hand gesture, a splash, anything a viewer needs to actually track frame by frame. Slower or steadier motion stretches more forgivingly even out of Slo-mo, because there's less change happening between the frames an editor has to stretch across a longer playback time.

Slowing a clip you filmed at normal speed

A clip that wasn't filmed in Slo-mo can still be slowed down, using iMovie's Speed slider dragged to the left. 1/2x plays at half speed. It's worth judging the result before committing to it: normal footage only has so many frames per second to begin with, so stretching it out to play slower means the same handful of frames now has to fill more screen time, which is what causes the stutter. Slo-mo mode avoids that because it captures far more frames per second at the moment of filming, giving the slow-motion playback much more source material to draw from. The smoothness comes from the extra data captured at record time, not from anything an editor does afterward.

Audio slowed down alongside the video tends to drop in pitch and can sound distorted well before the picture starts looking choppy, which is often the first sign that a clip has been pushed further than the footage can comfortably support.

Captions that stay in sync when the speed changes

Montaj doesn't slow footage down, but once a clip's speed is set the way you want it, word-by-word subtitle timing follows the audio exactly, so captions stay locked to what's being said even after the pacing changes. That matters more on slowed footage than it looks: a caption timed against the original pace will drift out of sync the moment the underlying audio stretches, and re-timing captions by hand after a speed change is its own separate chore. That's one less thing to re-check once you've slowed down a video on iPhone the way you wanted it.