Hey Martin
Are you ingesting assets into Streamline that already contain XMP metadata, or are you trying to write metadata using Streamline? Version 4.2 of Streamline introduced the support for writing of metadata to compatible file formats. Secondly, if you are using Streamline to write the metadata, you will need to (re)ingest the assets using a specific mapping profile. The mapping profile will allow your entity fields to write the data.
Feel free to reach out to me at awisniewski@rossvideo.com
#XPression