The iPhone 5s introduces a new Slo-Mo camera mode, in which you can create videos that seamlessly slide from normal video to super-smooth slow-motion action and back again. That smooth motion happens because in Slo-Mo mode, the iPhone 5s is shooting video at 120 frames per second (instead of the usual 30 fps), so when it’s running at a quarter-speed, it’s still running at the same frame rate as regular video. There’s not the stutter of repeated video frames that you’d see in a fake slow-motion effect.
On the iPhone 5s itself, the Camera app can let you quickly make and share (albeit with some complications) slow-motion videos. But back on your Mac, things get a little more interesting.
Copy a Slo-Mo video back to your Mac, and you get a normal QuickTime movie file. Open it up in QuickTime Player, and you’ll see a regular old video playing back at regular speed—no slow-motion at all, even if you set in and out points on your iPhone 5s.
If you look closely, though, you’ll notice that everything seems a little smoother than a normal video does. That’s because you’re watching that video play back at 120 fps. All the information necessary to make a slow-motion video is there—it’s just all playing back at normal speed rather than one-quarter speed.
The good news is, you can import this video into iMovie (or Final Cut Pro, or any other video editor you can name) and create your own slow-motion effect. The Camera and Photos apps on the iPhone 5s will only let you create a single slow-motion region; in a video editor, you can flip into and out of slow-motion mode as many times as you want.
In iMovie, just import the movie file as you would any other iPhone video. you’ll see that the thumbnails are tagged with a small icon in the bottom-left corner that reads “120,” because it’s a 120-fps video.
To emulate the iPhone’s video effect in iMovie, add the clip to your iMovie project and then split it into three parts—the beginning, the middle part (which you’ll switch into slow motion), and the ending. Then select the middle part and choose Clip > Slow Motion > 25%. You’ll have to give iMovie a few seconds to optimize the clip, and that’s it.
Using this approach, you can shoot a long high-frame-rate sequence using the Slo-Mo mode and then create a video that switches into and out of slow motion as often as you like. Imagine a diver slowly jumping off the diving board, then moving at full speed until just before hitting the water. Or a skateboarder who slows down every time she’s airborne.
Embedded below is a video we shot on the iPhone 5s but edited in iMovie on the Mac.