I have a late 2012 iMac running Catalina (10.15.7) as it's too old to upgrade to Big Sur. Photos are synced from my phone with iCloud.
I'm unable to export HEVC videos to other formats. When I drag and drop to the finder, the cursor shows a green plus sign but nothing happens. No error, but no video either.
When I choose
File > Export > Export 1 Video… I get an unable to export error:
Unknown error (0).
The videos play fine in Photos. I can export them using
File > Export > Export Unmodified Original, and they show up as HEVC videos in .mov containers. They play fine in the Finder with Quicklook, and I can open them in Quicktime Player, although
File > Export As has all its options greyed out.
This seems to apply to every HEVC video in my library. Other formats (e.g. H.264) work normally. I have a newer iMac running Big Sur synced to the same iCloud library, and I can export normally there.
Apple says HEVC support was introduced in High Sierra, so Catalina should be fine. And there must be some support, since I can watch the videos.
What could be causing this and how can I fix it?