Add --exiftool-merge

[RhetTbull]

--exiftool overwrites any keywords, persons, etc in the file when exporting with the data in Photos. Add a --exiftool-merge flag that causes exiftool to first read the original data then merge it and de-dup it with the new data before writing

Given the behavior is already to overwrite the existing metadata, maybe an option for --merge-exifdata that would cause osxphotos to read all exifdata on the original file then merge it before writing it back to the file.

Originally posted by @RhetTbull in #292 (comment)

[RhetTbull]

Fixed in v0.38.18

[narensankar0529]

Would this only work if the exif is stored directly in the file? Is it possible to support merging for the XMP and JSON sidecars?

[RhetTbull]

Yes. It works with --sidecar as well as --exiftool. The merge options read keywords and/or persons from the original file's exif data and write it to the sidecar and/or the exported file's exif data.

[narensankar0529]

Sorry - just to double confirm - If I use an external app to write tags to the XMP, Keywords and/or PersonInfo, then osxphotos will not overwrite it if I use the --exiftool-merge parameter - right? so it would read the existing XMP and the dc:Subject and then potentially merge with new keywords from the Photos database and write out the sidecar?

[RhetTbull]

No, sorry, I misunderstood your question. --exiftool-merge-keywords/--exiftool-merge-persons options only read the exif data directly from the original image in the Photos library. There is no support for reading the XMP or json data -- osxphotos writes those but does not read them. If you modify the XMP or json files outside osxphotos, they'll be overwritten the next time you run export with --update. osxphotos is an export tool not an asset management system. You could use exiftool to read the XMP file and write back to the image using something like this:

exiftool -tagsfromfile SRC.xmp -all:all DST.jpg

If you ran osxphotos export --update again with --ignore-signature option it would not overwrite the updated image files.