Shot a video on my iPhone 8 Plus (screenshot from Image Capture)
via iCloud Photos, it shows up. Here's the info screen:
When I export the video from Photos and choose "4K"
I'm given this file:
If I manually drag the video from Image Capture to Finder, I'm given this:
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Here are the two files side by side in Finder upper is from Photos, lower is from the iPhone via Image Capture:
Why is Photos for Mac giving me a highly compressed 720P version when I explicitly am asking for 4K. If I drag and drop the movie from Photos to Finder, I'm given the same file 720P, 46 megabytes.

via iCloud Photos, it shows up. Here's the info screen:

When I export the video from Photos and choose "4K"

I'm given this file:

If I manually drag the video from Image Capture to Finder, I'm given this:

---
Here are the two files side by side in Finder upper is from Photos, lower is from the iPhone via Image Capture:

Why is Photos for Mac giving me a highly compressed 720P version when I explicitly am asking for 4K. If I drag and drop the movie from Photos to Finder, I'm given the same file 720P, 46 megabytes.