Write xattr if CGMetaData write fails (was Video files can't edit kMDItemAuthors and kMDItemTitle metadata)

[Jeffrey-deng]

First of all, thank you for making such a useful tool！！

Videos cannot be added, deleted, backed up and restored for kMDItemAuthors and kMDItemTitle, but I successfully edited these for text file.
my system version is macOS Ventura 13.6

[RhetTbull]

I've been able to replicate this and I think this is expected behavior though I'm not sure exactly how to document it. Not all tags are writeable and some tags are writeable for certain file types while are readonly for other file types.

Some of metadata map directly to EXIF and XMP metadata in images. For example, if you set XMP:Title in an image (exiftool -title=Title IMG_1234.jpg) then kMDItemTitle will reflect the title in the XMP metadata. This is done by Spotlight indexing files. But you can't change this with osxmetadata because then the Spotlight metadata would not match the image metadata. OSXMetaData doesn't enforce this -- it's a behavior of the underlying macOS API (which is undocumented). For some reason, seting XMP:Title or Quicktime:Title on a video does not cause kMDItemTitle to be updated though. Again, this isn't osxmetadata doing this but the mac API. However, for file types that do not support embedded metadata (such as a text file), then macOS does let you set these fields. I've tried with several other file types and the behavior is consistent.

There may be a way to determine which fields can be written for which file types but as I'm using an undocumented API I'd have to dig in to find this which I don't have time to do currently. Perhaps in the future if I have some time I can look into this.

One thing that osxmetadata could do is verify the write was successful and give an error if not. For example, in your case it would write the title, read the title, then flag an error if the read title was not what was expected.

[Jeffrey-deng]

Thanks for such a detailed reply!

I was able to set these fields using xattr before, and Spotlight was able to recognize them. （I used your tool and it worked when I backed up but not work when I restored）

I'm looking for a tool to backup file metadata before uploading to NAS, your metadata backup method is a good idea!

[RhetTbull]

was able to set these fields using xattr before, and Spotlight was able to recognize them. （I used your tool and it worked when I backed up but not work when I restored）

You can set them via xattr but that's not the same as setting them in the Spotlight database. If Spotlight will still index them then osxmetadata could write the xattr if the "official" write fails. osxmetadata used to write only xattr but I found this meant that Spotlight didn't always index these and then discovered the private API to set the metadata so I switched to that method. I'll look at adding a fallback to set the xattr (maybe with a warning) if the CGMetaData write fails.

I'm looking for a tool to backup file metadata before uploading to NAS, your metadata backup method is a good idea!

I originally wrote this for a similar reason -- storing files in a cloud sync that didn't support xattr.