Cutaway to portrait image displays on top of video instead of on black background
I am making a movie in 16:9 landscape aspect ratio and I want to cutaway to a portrait image. I was hoping that the movie would completely cutaway to the portrait image with the space on either side filled in black (i.e. the portrait image would be displayed on a black background). However, the image simply appears on top of the video like a picture in picture. Is there any way around this? Is there any way to get imovie to automatically put black bars on either side of a portrait image so it can be used in a regular landscape project?
MacBook Pro 13″, macOS 10.14