iMovie has a “Snap to Beats” feature (turned on by default) that lets you easily align video clips and still images to beat markers added to background music. With this feature on, when you drag a video clip near a beat marker, the clip snaps to alignment with the marker and stays “pinned” to that marker (as long as you don’t move the video clip elsewhere).
As a result of pinning, if you move a beat marker, the clip that is pinned to the beat marker moves with it. Therefore, if you move the marker to the left, iMovie automatically lengthens the video clip that’s pinned to that marker and shortens the preceding clip by the same amount. If you move the marker to the right, iMovie automatically shortens the video clip that’s pinned to that marker and lengthens the preceding clip by the same amount.
“Snap to Beats” applies only when you’ve added beat markers to a background music track following the steps described below. It’s a useful feature if you want to create a project with a music video feel because it lets you add video and photos so that they appear in time with the music.
To synchronize using “Snap to Beats”:
Add a background music track to the project.
The colored well that represents the track starts out as a small square, but it grows as you add video clips to it.
Add beat markers to the background track.
Add video clips to the project.
The clips are automatically added at beat markers, starting from the beginning of the music track.
iMovie automatically trims or extends each clip (from its end) to fit between the beat markers, so it’s unnecessary to be exacting when you select video to add. The portion of the selected Event clip that iMovie actually adds to the project is underlined in orange in the Event browser.
When you add other elements to your project—titles, sound effects, voiceover tracks, and so on—they also snap to the beat markers as you drag them in the Project browser. A vertical yellow line appears when they have “snapped.”
You can add a transition effect to the project between two existing video clips, but it causes the rest of the project after the transition to be out of sync with the beat markers. However, if you add a transition after the last clip in the project, iMovie makes the preceding video clip and the transition fit in the space between beat markers by shortening the video clip. You can then continue adding video clips that snap to the beats.
In the Clip Trimmer, you can add other beat markers to the music track wherever you want. When you do so, iMovie splits the clip where you added the marker.
To turn off “Snap to Beats”:
You can turn off “Snap to Beats” at any time during the creation of a project. That means you can start the project with it on and then turn it off to give yourself more leeway to move and edit elements of the project.
Choose View > “Snap to Beats” (make sure the command is deselected in the menu).
The View menu appears in a light gray bar across the top of your computer screen.
When “Snap to Beats” is off, you can still add beat markers and use them to manually align elements to the beat. When you add a marker to a portion of the music that already has video, the video clip isn’t split at the marker. You can also move any existing beat markers without shortening or lengthening the video clips on either side.
To replace video clips in your project, keeping existing beat markers aligned:
After you’ve synchronized video with beat markers added to background music clips, you can replace a video clip in your project so that the new clip is the same duration as the one it’s replacing. That way, all the subsequent clips in the project stay aligned with the beat markers.
Make sure Advanced Tools are turned on.
Make sure “Snap to Beats” is turned on; choose View > “Snap to Beats” (make sure the command is selected in the menu).
Open the project you want to work on so that it’s showing in the Project browser.
In the Event browser, select a clip or a frame range you want to add to your project, and then drag it over the clip in the Project browser you want to replace.
Release the mouse button when you see a green Add (+) symbol.
In the menu that appears, choose one of the following options:
Replace: Replaces the existing clip with the new clip from the beginning of the new clip. If the new clip isn’t precisely the correct length, iMovie automatically shortens or extends it from the end so that its length is equal to that of the clip it’s replacing.
Replace from End: Replaces the existing clip with the new clip from the end of the new clip (meaning that the end of the new clip aligns with the end of the existing clip). If the new clip isn’t precisely the correct length, iMovie automatically shortens or extends it from the beginning so that its length is equal to that of the clip it’s replacing, and so that the endpoint isn’t modified.
Replace at Playhead: Replaces video in the project with video of an equal length from the Event, placing the beginning of the selected Event clip where the playhead appears in the project. iMovie shortens or lengthens the Event clip, in both directions if necessary, to fill the space used by the clip it’s replacing.