How can I modify an XMP meta of a file?

Question

I'm interested in seeing if I can modify some XMP within an image file. I'm using the following code:

        var items = MetadataExtractor.ImageMetadataReader.ReadMetadata(_filename);
        foreach (var item in items)
        {
            if(item.Name == "XMP")
            {
                var y = new XmpCore.Impl.XmpMeta();
                var xmp = item as MetadataExtractor.Formats.Xmp.XmpDirectory;
                foreach(var xd in xmp.XmpMeta.Properties)
                {
                    
                    if(xd.Path == "drone-dji:AbsoluteAltitude")
                    {
                        var alt = Convert.ToDecimal(xd.Value.Substring(1,xd.Value.Length-1));
                        alt -= 100;
                        xmp.XmpMeta.SetProperty(xd.Namespace, xd.Path, alt.ToString());
                        
                    }
                }

                xmp.SetXmpMeta(xmp.XmpMeta);
            }
        }

I know I'm missing something breathtakingly obvious but I don't know this library well enough to figure it out.

No exceptions come up but when I open up the file the XMP field is still the same. When I iterate thru the xmp properties after I set the property it does reflect correctly but when I end the program the file stays the same. I'm sure there's something to do with writing back to the image path but I have no idea where in this library I do that. Any help would be greatly appreciated.

Answer 1

MetadataExtractor doesn't support modifying files. You can update the data structure, as you show, but there's no way to write those changes back to your original file.