there is an old, non functional plugin for accessing cddb (hopefully also for freedb/gnudb) and I am tempted to try to revitalize it. But let me ask a curious question before digging further into it:
Is it possible to get infos from these sources (cddb/freedb/gnudb) and submit them in turn to Musicbrainz, ofcourse after checking its correctness and validating/supplementing it?
Background: Long time ago I supplied infos to cddb/freedb and these infos are currently not available on MusicBrainz, but really I do not want to type in everything again.
I’m not sure what the question is here. I don’t think there’s an API for MusicBrainz that includes submitting release data, and besides that, I’m not sure why you’d do this as a rhythmbox plugin rather than standalone.