How to add a comment to a JPEG XL image?

[tokujin]

Hi, I'm trying to add a comment to a jxl screenshot I made with mpv. I usually put comments in the tag description but if you suggest another one I'll take the suggestion.

I've installed IO::Compress::Brotli as suggested here (though I don't know how to check if it works) and I've tried some variants of

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exiftool -v3 -xmp:description="aaa" lossy.jxl(adapted from this thread). I've tried adding -api compress=1 as the Jpeg2000 Tags page says "ExifTool will read/write Brotli-compressed EXIF and XMP in JXL images, but the API Compress option must be set to create new EXIF and XMP in compressed format."

In all cases the result has been

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Writing XMP-crd:Description if tag exists
Writing XMP-crs:Description if tag exists
Writing XMP-dc:Description
Writing XMP-xmp:Description if tag exists
======== lossy.jxl
Rewriting lossy.jxl...
  Error = [minor] Will wrap JXL codestream in ISO BMFF container for writing
Error: [minor] Will wrap JXL codestream in ISO BMFF container for writing - lossy.jxl
    0 image files updated
    1 files weren't updated due to errors

I have ExifTool v. 12.70.

[Phil Harvey]

Raw JXL codestream files can't contain metadata.

Use the -m option to ignore the minor error and allow ExifTool to wrap the JXL codestream in a BMFF container.

- Phil

[tokujin]

Awesome! Thanks Phil :-)