Thank you for your excellent libraries (I see that you wrote the underlying heif/c libs on which this plugin relies).
I have used the windows API to convert from a Canon CR2 raw format (14bit? depth, RGB) to HEIC: https://github.com/DavidAnson/ConvertTo-Heic
The resulting HEIC is apparently valid according to Windows native editors, but can't be opened in Gimp. Resulting in an error dialog box which reports: "Loading HEIF image failed: Invalid input: No 'meta' box".
I attach an example image below:
IMG_6860.CR2.heic.zip
Is there a limitation of the plugin? or one of the underlying libraries?