You can allow any viewers to download the HD mp4 videos of a collection or standalone videos as a backup. To enable this for a video or collection, toggle the "Allow Video Downloading" in the Share Link and/or Digital Delivery tab (they are controlled separately). After doing so, viewers will see a download icon in the upper-right of the video or collection where they will be able to download the mp4 files.
Downloading works on both mobile and desktop. iPhone users must have iOS 13 or above to support file downloading from Safari.