Well, i nx-term I ran this:
rm .meta_storage
so now I have a clear library in mediaplayer. I have metalayer-crawler disabled though, so I still get the message "refreshing library" (or similar) every startup. This message is easy to banish, just tap on it, but there seems to be no way the library will ever refresh.

Does anyone know how to either:
1....re-enable metalayer-crawler.
or...2....get mediaplayer library to refresh without re-enabling metalayer-crawler (but then I guess there will always be issues after additions or deletions of media as the crawler won't be running, thus no updating).

Many thanks.