If you download the musicsummerytest.bundlezip in the 3rd post down in this thread Music metadata from Tag or File and download it, then unzip it to your plugin folder located within the plex directory.
You will then need to in the web interface go to agents under settings and under albums & artists make sure you have them set up in the following order:
Personal Media Artists
Local Media Assets
Artist Summary Agent
Please be mindful this will only work on a fresh install of a music library and when you set the library up you would need to have the settings as follows:
Scanner= Plex Music Scanner
Agent= last.fm
When you load the library up it should then scan the suymmary.txt files within you album and artist directory. Please bear in mind these .txt files need to be saved as UTF-8 files from with notepad otherwise plex will not pick them up at all.
It can be quite a laborious process if you have not already got the files in .txt format especially if you have a large library like I have.
Hope that helps
