Make a video slow motion

Divide the frame rate the clip was filmed at by how many times slower you want it. If the answer is 24 or more, the slow motion will look smooth on its own; below that, frame blending does the work.

• 240 fps (iPhone and many Android slow-motion modes): smooth at any speed here.
• 120 fps: smooth down to 0.25×.
• 60 fps: smooth at 0.5×; blending helps at 0.25×.
• 30 fps (most normal phone video): fine at 0.75×, good with blending at 0.5×, dreamy and soft at 0.25×.
• 24 or 25 fps (cameras and films): best kept at 0.5× or faster.

This tool reads up to 60 frames a second from the clip and writes a 30 fps MP4, so at 0.5× a 60 fps clip uses every real frame. It can’t invent detail that wasn’t filmed: very fast movement filmed at 30 fps still blurs at 0.25×.

Filming in Slo-mo

The Camera app’s Slo-Mo mode records at 120 or 240 frames a second. In Photos, open the video and tap Edit: the bar under the frames shows where it slows down, and you can drag its handles to change which part plays slowly. That’s the best quality you can get, but only for clips filmed that way.

Slowing a normal video

Photos can’t slow down a video that was filmed normally. Two free options:

1. In Safari, open this page, tap Choose a video, pick the clip, choose a speed and tap Export slow motion, then Share or save to Photos.
2. In iMovie for iPhone, add the clip to a movie project, tap it in the timeline, tap the speed button and drag the slider towards the tortoise (as slow as 1/8×). Then export the movie.

Slo-mo clips from the Camera app also open here. They hold far more frames than a normal video (this tool reads up to 60 a second), so they slow down very cleanly.

The export contains only the section inside the window on the strip, slowed down. To keep the rest at normal speed (the sports-replay effect), export the slow part here and put it between the normal-speed parts in an editor such as iMovie, CapCut or Premiere Pro.

For a slow part inside a looping clip, the slow-motion boomerang has a Slow-mo section that slows just the middle of the movement, both ways. To run footage backwards rather than slower, use the video reverser; its Speed setting also goes down to 0.5× for a slow reverse.

Sound is off by default. When you turn it on, the audio slows with the picture, the way a tape played slowly does, so it also drops in pitch: an octave lower at 0.5×. That suits dramatic effects and engine noise; for voices or music, leave sound off and add a track in your editing app instead.