This is a very bare bones config file to write the XMP-audio/XMP-video tags that I think can be used in DigiKam. See the links in the file for more details
Due to a lack of samples and the vague sources, some of these are most certainly broken. I've attempted to make a guess as to how the GPS tags and the Orientation tag are written, but I could be wrong.
There are 318 XMP-video tags and 45 XMP-audio tags. You can use this command to get the full list of tag names
exiftool -config DigiKam_Audio_Video_tags.config -list -xmp-audio:all -list -xmp-video:all