midi-converter.js

import fs from "fs";
import path from "path";
import midiConverter from "midi-converter";

let name = "clair-de-lune";
let file = fs.readFileSync(path.join(__dirname, `${name}.mid`), "binary");
let json = midiConverter.midiToJson(file);
let ticksPerBeat = json.header.ticksPerBeat;
let tracks = [];

json.tracks = json.tracks.forEach((track, i) => {
  let time = 0;
  let memo = [];

  tracks[i] = [];

  track.forEach((items, j) => {
    time += items.deltaTime;

    if (items.subtype === "noteOn") {
      let note = {};

      note.time = time;
      note.track = i;
      note.noteNumber = items.noteNumber,
      note.velocity = items.velocity;

      if (!memo[items.noteNumber]) {
        memo[items.noteNumber] = [];
      }

      memo[items.noteNumber].push(note);

      tracks[i].push(note);
    }

    if (items.subtype === "noteOff") {
      if (!memo[items.noteNumber]) {
        console.log([ i, j, time ], items.noteNumber + " NOT exists?")
      } else {
        memo[items.noteNumber][0].duration = time - memo[items.noteNumber][0].time;
        memo[items.noteNumber].shift();
      }
    }
  });
});

let events = tracks.reduce((a, b) => a.concat(b), []);
events.sort((a, b) => a.time - b.time);

fs.writeFileSync(`${name}.json`, JSON.stringify({
  name, ticksPerBeat, tempo: 120, events
}, null, 2));