In an attempt to reclaim some space on my iPhone, I discovered that iMovie was one of the biggest data hogs. (You can see how your iPhone’s storage is being allocated by checking Settings > General > iPhone Storage.)
No wonder: all of Apple’s current iPhone models capture up to 4K resolution, which occupies approximately 350MB of storage per minute (or 170MB per minute if you’re using the new HEVC format under iOS 11). Even the default setting of 1080p at 30 frames per second (fps) uses 130MB per minute of H.264 video (60MB for HEVC).
A lot of those gigabytes were old iMovie projects that didn’t need to stay on the iPhone. I could have just deleted them, but I want to keep the option of editing old video projects later. If iMovie is hoarding storage on your iPhone or iPad, here are some safe ways to clean it up.