Split M4B books chapters

split.js

/**
 * Needs MP4Box binary to work
 * $> node split.js "Atomic Habits.m4b"
 */

const { execSync, exec } = require('child_process')
const cheerio = require('cheerio')
const escape = string =>
  string
    .split('')
    .map(char => (char.match(/[a-z0-9]/i) ? char : '\\' + char))
    .join('')
const exeCat = command =>
  new Promise((resolve, reject) => {
    exec(
      command,
      { maxBuffer: 1024 * 1024 * 100 },
      (error, stdout, stderr) => {
        resolve(stdout.toString() || stderr.toString())
        if (error !== null) {
          reject(error)
        }
      }
    )
  })

const timeToSeconds = time => {
  const [h = 0, m = 0, s = 0] = String(time)
    .split(':')
    .map(parseFloat)
  const seconds = h * 60 * 60 + m * 60 + Math.floor(s)
  return seconds
}
const pad = (n = 0, l = 2) => `${1e12}${n}`.slice(l * -1)
const splitByChapter = inputFileName => {
  const inputFile = escape(inputFileName)
  const inputName = inputFileName
    .split('.')
    .slice(0, -1)
    .join('.')
  return exeCat(`MP4Box -diso -std ${inputFile} | cat`)
    .then(xml =>
      cheerio.load(xml, { xml: { normalizeWhitespace: true } })
    )
    .then($ =>
      $('ChapterListBox')
        .children()
        .map((i, el) => $(el).attr())
        .toArray()
    )
    .then(list =>
      Promise.all(
        list.map(async ({ name, startTime }, i) => {
          const start = timeToSeconds(startTime)
          const fileName = escape(
            `${inputName} - ${pad(i, 3)} - ${name}`
          )
          let end = ''
          if (list[i + 1]) {
            end = timeToSeconds(list[i + 1].startTime)
          } else {
            const info = await exeCat(
              `MP4Box -info ${inputFile} | cat`
            )
            const durationMatch = info.match(
              /(?:Computed Duration) (\d{2}:\d{2}:\d{2}.\d+)/m
            )
            end = durationMatch
              ? timeToSeconds(durationMatch[1])
              : ''
          }
          const chap = await exeCat(
            `MP4Box -splitx ${start}:${end} ${inputFile} -out ${fileName}.mp3`
          )
          return chap
        })
      )
    )
}
if (process.argv[2])
  splitByChapter(process.argv[2])
    .then(chapters => (Array.isArray(chapters) ? chapters : []))
    .then(results =>
      results
        .map(out =>
          out
            .split(/\r|\n/)
            .filter(line => !line.match('ISO File Writing'))
            .filter(line => !line.match('Splitting'))
            .map(line => line.trim())
            .filter(String)
        )
        .map(console.log)
    )