iMovie for Mac: Add video clips and photos from your photo library
All the photos and video clips in your Photos, iPhoto, and Aperture libraries are automatically available for use in iMovie.
Add media from your photo library
In the Libraries list, select your Photos, iPhoto, or Aperture library.
Tip: It’s a good idea to use Photos to import photos and video clips you want to use in iMovie. For more information, see Photos Help.
Click the pop-up menu at the top of the browser, choose a content category, and then scroll through the thumbnails of photos and video clips in that category.
Select the photo or clip you want to use to see a preview in the viewer.
Do one of the following:
Insert the photo or video clip: Drag it to the timeline between clips or between a clip and a transition.
As you drag, a blue box appears in the timeline, indicating where the photo or clip will appear in the timeline.
Replace a clip: Drag the photo or clip on top of a clip in the timeline.
As you drag, a white border appears around the clip in the timeline. When you release the mouse button, choose Replace from the menu that appears. The photo or clip replaces the clip in the timeline.