iPhone iMovie project videos not loaded

One thing I did not know before is that a project in the iMovie uses the materials from the iPhone, instead of making hard copies. I deleted a lot of the original video clips from the photo library to save space, then when I opened the project in iMovie, it said videos are being downloaded from icloud, but it stuck there. This means the videos are no longer available. 

The end of the world?

Fortunately, I used the Image Capture before to export the videos of iPhone photo library to my Macbook. Therefore, I can use the following to recover these iMovie projects.

1. Use cable to connect iPhone with Macbook. 
2. Open finder, click on the iPhone disk on the left panel.
3. In the Finder "iTunes", click on Photos
4. Sync the photos from local directory with the videos that are needed by the project to iPhone
5. Open iMovie on iPhone and reload the project, export the videos to photo library

If you want to delete these videos from iPhone again, you can't delete them from you phone directly this time! I found the following helpful:

1. Use cable to connect iPhone with Macbook. 
2. Open finder, click on the iPhone disk on the left panel.
3. In the Finder "iTunes", click on Photos
4. Deselect "sync" the folders to iPhone, and choose remove photos from iPhone, click 'Apply'
5. Now the videos are still on the phone. Because it is not updated immediately. To immediately delete these videos, go to iPhone's settings - photos, enable 'Photo'-'ICLOUD'- iCloud Photo. This will remove all the synced photos. Then disable the iCloud Photo.