I have a video in the Photos library of the Photos app on my Mac.
If I right-click it and select "Get Info" - it shows that the video is 1920x1080.
Next, I share it to iCloud Photo Sharing.
Then - if I right-click the resulting video in the Shared album - it shows that the video is now 1280x720.
So - how can I share videos without reducing the quality?
As a random aside... does anyone have any tips for how to search Google for help for an app as generically named as "Photos"?