This command enables you to add your own song list to EU4 by generating songs.txt and music.asset from local .ogg files.
go get -u github.com/tadayosi/eu4-songs-gen
Running the command searches .ogg files in the current directory and generates songs.txt and music.asset there:
eu4-songs-gen
You can also specify the directory where .ogg files are located and songs.txt and music.asset are generated there:
eu4-songs-gen songs/
Rename the generated songs.txt and music.asset to something like custom-songs.txt and custom-music.asset and copy them to the EU4 music/ directory (which is typically ~/.local/share/Steam/steamapps/common/Europa Universalis IV/music/ for Linux) as well as your custom .ogg files.
NOTE: The name of a .ogg file must only include alphabets (a-zA-Z), numbers (0-9), and underscore (_). Otherwise the game won't load the song list correctly.
For more info, see the help:
eu4-songs-gen -h