I don’t have Lightroom or any other DAM software but I wanted to add keywords directly into files rather than having XMP sidecars.
To start with I used ExifTool to add keywords to the IPTC:Keywords tag but, although they were visible in macOS Finder, they were not visible in PhotoLab
Then someone in these forums hinted at using the XMP:Subject tag. Sure enough, if you have either software that is capable of adding keywords to this tag or the command line ExifTool, you can add keywords.
exiftool -Subject=keyword1 -Subject=keyword2 -Subject=etc -overwrite_original filename.ext
Keywords added like this are visible both to operating system search and within PhotoLab.
I don’t think that will work. Only the last keyword will be written.
The = sign is overwriting everything in that field. Use += for the second one and further. Or use an argument list.
You can also synchronize the iptc and xmp keywords.
Well, it does work correctly as long as all the keywords are written at the same time. The += syntax is for when you want to add more keywords to those that are already in the file.
A while back when I was still using Luminar (who still don’t have the ability to edit keywords — glad I didn’t wait around) I came up with a means of adding keyword hierarchies to my DNG files in the same manner as Lightroom.
This blog post I wrote about it may contain useful information for others.