why not listen to the mp3 if they are available ?

If you mean why I convert then from mp3 to ogg then it simply because game doesn't support mp3. Also, original music still needed normalization cause volume was very low.

I mean what's the point of doing this operation ? why not just listen to the mp3 while playing as that wouldn't alter the quality

There have several other mod that add musics to the game that come from other game, why do you come to my mods to ask stupid questions like this and not the others mods ?

My answer will be "why not", it's more simple for the user, it's also to share with other good musics that match factorio lore. At this point why not ask why factorio bother to have ambient music and not just tell user to open vlc. Also, these mp3 come from AMIGA they have already been "altered", the conversion to ogg using 128 kb/s should be transparent and is lower in file size. Also, I set an "hero-track" and added some settings that you can't do using VLC.

Don't come to my mods and do what you do in the forum plz bye