In iMovie, you can make videos by using photos, voiceovers and music without any video footage. iMovie stores your videos in the Event Library. The events library allows you to organize your videos by events and dates. So that, you can find those videos easily and clips are easier to navigate. You can upload those videos to Google Drive easily and share them with other people in the world. You can upload any kind of a file to Google Drive including video. If you want upload iMovie videos to Google Drive on your iPhone, then you have to save those videos from iMovie to your camera roll.
You can install PicBackMan's Google Drive uploader for Mac from the website and start backing up photos and videos.