It's a tool to generate Minecraft (Bedrock) music from MIDI files.
1. Generate the music MCPack.
2. Download the NBO Base MCPack.
3. Open both MCPacks to import them to Minecraft.
4. Add both behavior packs to your world (NBO Base, and your music MCPack).
5. In the world, run /function NBO/Init to initialize (you also can run this later to reset).
6. Spawn a repeating command block with the command /function NBO/Loop
7. For each part your track is split into, spawn a repeating command block with the commands /function NBO_SongNameHere/PartNumberHere.
(note: part number starts from 1 onwards)
8. Activate both command blocks.
The program converts MIDI notes to Noteblock sounds with the appropriate pitch and volume (velocity of MIDI), repitching it as necessary.
It uses a scoreboard objective music to keep track of each player's current play position.
Then, the playsound commands are executed with scoreboard selectors for specific times to play the song.
It's fun, and I couldn't find anything to do stuff like this for Bedrock Edition.