Speeding up or slowing down a clip is a simple process in iMovie—once you know how to do it.
Start by clicking on or mousing over a clip in your timeline, to reveal the little blue icon with a white gear.
Select “Clip Adjustments” from the dropdown menu.
This will open a gray window with a lot of options, which are worth exploring to discover new ways of fine-tuning your movie and achieving complex effects.
You may see this in the middle of the window:
Don’t worry! It just means that iMovie doesn’t currently know enough about your video file to adjust its speed. Just click the button and make yourself a sandwich while it renders; once the file has been converted, you’ll be able to access the speed adjustment menus normally.
The menus we want look like this:
There are three different ways to adjust the speed of the clip from this window. The simplest is to drag the slider toward the turtle to make the clip slower, or toward the rabbit to make it faster. Here, I’ve moved the slider one notch toward the turtle.
However, if you do so you’ll notice that the two gray boxes with numbers in them will also change. The top box is the speed of the clip expressed as a percentage of the original speed; it tells me that when I slowed the clip down, I made it half its original speed. The bottom box is the duration of the clip at its new speed; it tells me that the clip is now 12 seconds long.
These boxes are great because they let you really fine-tune your speed adjustments. Simply type in a percentage, or a duration, and it will adjust the clip to your exact specifications!
And, as a bonus, if you want to make your video play backwards, you can do that here, too, simply by clicking the “reverse” box.