You might want to have a look at https://beets.io

kid3 can apply metadata based on the filename if that's useful for you (just things like title and track depending on how you name your files). I also use it for manually editing metadata once in a while, selecting multiple songs and setting the same artist or album tag is pretty easy to do.

I just installed such a tag editor a few days ago, what a coincidence. I don't know what operating system you are using, but the one I chose is a graphical tool Kid3 . There is also commandline tool just called id3v2 . Both tools should be in the repositories in your distribution. However, these are Linux only I guess.

Kid3 is okay to me. You can get basic information from the filename into the tags, by specifying format variables like %{track}-%{title} in example and then click "to Tag 2" in example. Opposite is also possible, to rename all files based on the information from the tags. Nothing is changed physically on the files, until you hit the Save button.

Manual Edit: If you want edit a field with same entry for multiple files, then on the left side of the view with the files, just mult select with mouse while holding CTRL or SHIFT key. Then on the right side where the tag editor is, enable one of the entries like "Album" by clicking to show the tick. That means this Album entry will be updated for all selected files. Now type something into the Album field to fill or change it, enter and I guess that's it.

Import: I did not use this functionality yet, but it has multiple import resources from Amazon, MusicBrainz and other places. The Import options are in the top left menu under "File".

I have not tagged music files in a very long time but last I did it was with easytag.

I haven't tried, but if you're on linux you could try puddletag. OneTagger is very powerfull too (and cross platform). I also have some extra tools that may help you in this guide I made here (it's a guide on how to semi-automatically download and tag music, for a windows pc).

eyeD3

Sorry to hijack the thread, but does anyone known a terminal tool I can use to auto-tag the odd album when I find one with bad tags?

Music is stored on the server and served read only, so gui tools are not convinient.

Picard is great, but gui.

I wonder if Jellyfin can find metadata like it does with movies. Perhaps via a plugin?. Apart from that, all functionality (e.g. streaming) works with music just like it does with videos and that's great!