Cannot write exif and tiff metadata in image file

Hi,

I have a public XMP text file containing exif and tiff metadata: http://ns.adobe.com/exif/1.0/ and http://ns.adobe.com/tiff/1.0/.

I want to write these XMP data in an image file and it doesn't work. I don't get any exceptions, just the metadata are missing in the image file.

C#

using (var xmpFiles = new XmpFiles())

{

      if (!xmpFiles.OpenFile("test.jpg", handler.FileFormat, OpenFlags.OpenForUpdate))

          xmpFiles.OpenFile("test.jpg", FileFormat.Unknown, OpenFlags.OpenUsePacketScanning | OpenFlags.OpenForUpdate);

     using (var xmpCore = new XmpCore())

     {    

          xmpCore.ParseFromBuffer(xmpPublic.ToString(), ParseFlags.None);

          if (xmpFiles.CanPutXmp(xmpCore))

               xmpFiles.PutXmp(xmpCore);

     }

     xmpFiles.CloseFile(CloseFlags.None);

}

Public XMP:

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">

  <rdf:Description xmlns:_ns_2="http://ns.adobe.com/tiff/1.0/" rdf:about="">

    <_ns_2:ImageLength>4252</_ns_2:ImageLength>

  </rdf:Description>

  <rdf:Description xmlns:_ns_3="http://ns.adobe.com/exif/1.0/" rdf:about="">

    <_ns_3:ApertureValue>8/1</_ns_3:ApertureValue>

  </rdf:Description>

</rdf:RDF>

Result XMP in image file:

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">

  <rdf:Description rdf:about=""/>

</rdf:RDF>

Does anyone can help with that problem?

Thanks,

Alexandra