I suffered the same problem as Force Google Music Player to refresh album art? but I fixed it manually. That is, downloaded a local copy of the music on my phone and manually updated each MP3's album art. However, the web copy is still bad.
If I "upload" the fixed mp3 files will it update the files rather than upload a duplicate of it?
I don't want to try and have the latter happen and have a huge mess to clean up.
Best Answer
ChrisF's answer is mostly correct, but I think it has a subtle error:
I don't think this is entirely true. When the Music Manager scans a file, it generates a hash of it (you can find this in the Music Manager local database - it's called the "client id"). Importantly, the hash attempts to depend only on the track's audio, not on filename or metadata tags (further details here).
This means that if you change the tags or filename, the Music Manager should recognize it as a change to an existing file and not create a duplicate.
That said, there are two wrinkles to their solution: