Does video quality compress when saving and exporting from the iCloud?
Compressed video
iPhone 6s Plus, iOS 11.2.5
Question marked as
iCloud Photo Library always has full resolution photos and videos. You don't export from the iCloud Photo Library, you download from it. Direct downloads to a Mac/PC from the iCloud Photo Library should be full resolution as well.
If you are downloading from a shared album, videos are downsized and limited to 5 minutes in length.