chipmunkbot3/util/convert-midi.js

const fs = require('fs')
const { Midi } = require('@tonejs/midi')

const instrumentOffsets = [
  54, // harp
  0, // basedrum
  0, // snare
  0, // hat
  30, // bass
  66, // flute
  78, // bell
  42, // guitar
  78, // chime
  78, // xylophone
  54, // iron xylophone
  66, // cow bell
  30, // didgeridoo
  54, // bit
  54, // banjo
  54 // electric piano
]

const instrumentNames = require('./instrument-names.json')
const path = require('path/posix')

function convertMidi (filepath, lyrics = undefined) {
  const midiData = fs.readFileSync(filepath)
  const midi = new Midi(midiData)

  const noteList = []
  let length = 0
  for (const track of midi.tracks) {
    for (const note of track.notes) {
      const mcNote = convertNote(track, note)
      if (mcNote !== undefined) {
        noteList.push(mcNote)
        length = Math.max(length, mcNote.tick)
      }
    }
  }

  noteList.sort((a, b) => {
    return a.tick - b.tick
  })

  // normalize volume
  let maxVolume = 0.001
  for (const note of noteList) {
    if (note.volume > maxVolume) {
      maxVolume = note.volume
    }
  }
  for (const note of noteList) {
    note.volume /= maxVolume
  }

  if (lyrics) {
    parseLyrics(midiData, midi, lyrics)
  }

  return {
    name: midi?.meta?.name ?? path.basename(filepath),
    notes: noteList,
    loop: false,
    loopPosition: 0,
    length
  }
}

function convertNote (track, note) {
  const midiPitch = note.midi
  const midiInstrument = track.instrument.number
  let mcInstrumentID = 0
  let mcPitchID = 0
  if (track.instrument.percussion) {
    if (midiPitch === 35 || midiPitch === 36 || midiPitch === 41 || midiPitch === 43 || midiPitch === 45 || midiPitch === 57) {
      mcInstrumentID = 1 // bass drum
    } else if (midiPitch === 38 || midiPitch === 39 || midiPitch === 40 || midiPitch === 54 || midiPitch === 69 || midiPitch === 70 || midiPitch === 73 || midiPitch === 74 || midiPitch === 78 || midiPitch === 79) {
      mcInstrumentID = 2 // snare
    } else if (midiPitch === 37 || midiPitch === 42 || midiPitch === 44 || midiPitch === 46 || midiPitch === 49 || midiPitch === 51 || midiPitch === 52 || midiPitch === 55 || midiPitch === 57 || midiPitch === 59) {
      mcInstrumentID = 3 // hat
    } else {
      return undefined
    }
    mcPitchID = 0
  } else {
    if ((midiInstrument >= 0 && midiInstrument <= 7) || (midiInstrument >= 24 && midiInstrument <= 31)) { // normal
      if (midiPitch >= 54 && midiPitch <= 78) {
        mcInstrumentID = 0 // piano
      } else if (midiPitch >= 30 && midiPitch <= 54) {
        mcInstrumentID = 4 // bass
      } else if (midiPitch >= 78 && midiPitch <= 102) {
        mcInstrumentID = 6 // bells
      }
    } else if (midiInstrument >= 8 && midiInstrument <= 15) { // chromatic percussion
      if (midiPitch >= 54 && midiPitch <= 78) {
        mcInstrumentID = 10 // iron xylophone
      } else if (midiPitch >= 78 && midiPitch <= 102) {
        mcInstrumentID = 9 // xylophone
      } else if (midiPitch >= 30 && midiPitch <= 54) {
        mcInstrumentID = 4 // bass
      }
    } else if ((midiInstrument >= 16 && midiInstrument <= 23) || (midiInstrument >= 32 && midiInstrument <= 71) || (midiInstrument >= 80 && midiInstrument <= 111)) { // synth
      if (midiPitch >= 54 && midiPitch <= 78) { // bit
        mcInstrumentID = 13
      } else if (midiPitch >= 30 && midiPitch <= 54) { // didgeridoo
        mcInstrumentID = 12
      } else if (midiPitch >= 78 && midiPitch <= 102) { // bells
        mcInstrumentID = 6
      }
    } else if (midiInstrument >= 72 && midiInstrument <= 79) { // woodwind
      if (midiPitch >= 66 && midiPitch <= 90) {
        mcInstrumentID = 5 // flute
      } else if (midiPitch >= 30 && midiPitch <= 54) { // didgeridoo
        mcInstrumentID = 12
      } else if (midiPitch >= 54 && midiPitch <= 78) { // bit
        mcInstrumentID = 13
      }
    } else {
      return undefined
    }
    mcPitchID = midiPitch - instrumentOffsets[mcInstrumentID]
  }

  return { time: Math.floor(note.time * 1000), instrument: instrumentNames[mcInstrumentID], pitch: mcPitchID, volume: note.velocity }
}

function parseLyrics (midiArray, midi, lyrics) {
  midiArray = new Uint8Array(midiArray)
  const midiData = require('midi-file').parseMidi(midiArray)

  midiData.tracks.forEach(track => {
    let lastTick = 0
    let currentTicks = 0
    track.forEach(event => {
      currentTicks += event.deltaTime
      if (event.meta && event.type === 'lyrics') {
        const time = midi.header.ticksToSeconds(currentTicks)
        const tick = Math.floor(time * 20)
        if (!lyrics[tick]) {
          lyrics[tick] = event.text
        } else if (tick === lastTick) {
          lyrics[tick] += event.text
        }
        lastTick = tick
      }
    })
  })
}

module.exports = convertMidi