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.
There’s a “120” tag for Slo-Mo videos in iMovie.
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.
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