Hi, I was wondering if anyone knew how to convert any standard audio file (mp3, wav ect) to SSEQ. I've been looking into modding the game and i ran into a roadblock here. I'm not sure if anyone can help me, but just putting the question out there.

Hi! I’m sorry to disappoint you, but that really isn’t how it works. I used to think that’s how it worked, but you need to make your own midi and convert it with the midi2sseq tool, or the built in one in NitroStudio. Either you can make your own midi, or you can download an existing one, and change the midi instruments to the ones that the sseq you want to replace have. To find out which instruments to use, export an sseq from nitrostudio into the midi format. A more in-detail explanation can be found here. I hope this helps! (And don’t use any of that mp3 to midi stuff online, as it’ll only result in catastrophe)

might also be worth noting that theres also a code hack that lets you use streamed music, if youre familiar with using code hacks. if you arent, then yeah, youll have to use midis as crook suggested.

Isn't streamed music kind of cheating though? :')

Nah, it's fine. But I find the process of getting sequential music into the game more interesting, especially if you use a MIDI with the NSMB soundfont.