Book Stitcher. Combine multiple mp3 files into a single MP3 file with metadata (for chapters etc.). It's great for audiobooks.

README.md

Book Stitcher

This is just something I hacked together to create an audiobook file out of CD audio files (complete with chapter marking metadata!)

Works great when used in combination with https://github.com/kentcdodds/podcastify-dir

npx https://gist.github.com/kentcdodds/e07f9106c63cc13a75adb0157700eb5b ./path-to-sorted-mp3s

path-to-sorted-mp3s
├── 01.mp3
├── 02.mp3
├── 03.mp3
├── 04.mp3
├── art.jpg
└── metadata.json

The art.jpg will be used for the album cover. The metadata.json will be used for ID3 tags. Should be something like this:

{
  "title": "Book Title",
  "artist": "Author name",
  "subtitle": "Some description",
  "albumArtist": "Author name",
  "copyright": "copyright info",
  "date": "1988",
  "year": "1988-01-01",
  "userDefinedText": [
    {
      "description": "book_genre",
      "value": "Children's Audiobooks:Literature & Fiction:Dramatized"
    },
    {
      "description": "narrated_by",
      "value": "BBC"
    },
    {
      "description": "comment",
      "value": "Some description"
    },
    {
      "description": "author",
      "value": "Author Name"
    },
    {
      "description": "asin",
      "value": "49201153"
    }
  ]
}

bin.js

#!/usr/bin/env node

const path = require('path')
const fs = require('fs')
const mm = require('music-metadata')
const NodeID3 = require('node-id3')

// to convert files from m4a to mp3
// for f in *.m4a; do ffmpeg -i "$f" -codec:v copy -codec:a libmp3lame -q:a 2 newfiles/"${f%.m4a}.mp3"; done

/*
books
├── 01
│   ├── 1-01.mp3
│   ├── 1-02.mp3
│   ├── 1-03.mp3
... etc...
│   ├── art.jpg
│   └── metadata.json
├── 02
│   ├── 1-01.mp3
│   ├── 1-02.mp3
... etc...
*/

createBook(path.resolve(process.argv[2]))

async function createBook(base) {
  let specifiedTags
  const metadataPath = path.join(base, 'metadata.json')
  try {
    specifiedTags = require(metadataPath)
  } catch (error) {
    console.error(`
Make sure you have a metadata.json file at "${metadataPath}" with the audio files:

{
  "title": "Book Title",
  "artist": "Author name",
  "subtitle": "Some description",
  "albumArtist": "Author name",
  "copyright": "copyright info",
  "date": "1988",
  "year": "1988-01-01",
  "userDefinedText": [
    {
      "description": "book_genre",
      "value": "Children's Audiobooks:Literature & Fiction:Dramatized"
    },
    {
      "description": "narrated_by",
      "value": "BBC"
    },
    {
      "description": "comment",
      "value": "Some description"
    },
    {
      "description": "author",
      "value": "Author Name"
    },
    {
      "description": "asin",
      "value": -49201153
    }
  ]
}
    `.trim())
    throw error
  }

  const {title} = specifiedTags

  const files = fs
    .readdirSync(base)
    .filter(n => n.endsWith('.mp3'))
    .map(n => path.join(base, n))
  const metadatas = await Promise.all(
    files.map(async filepath => {
      const meta = await mm.parseFile(filepath)
      return {
        filepath,
        duration: meta.format.duration,
        title: meta.common.title,
      }
    }),
  )

  const outputFilepath = path.resolve(`${title}.mp3`)

  const glob = path
    .join(base, '*.mp3')
    .replace(process.cwd(), '')
    .replace('/', '')
  const outString = JSON.stringify(outputFilepath)
  await execShellCommand(
    `ffmpeg -y -f concat -safe 0 -i <(for f in ${glob}; do echo "file '$PWD/$f'"; done) -c copy ${outString}`,
  )

  const chapters = []
  let startTimeMs = 0
  for (let fileIndex = 0; fileIndex < metadatas.length; fileIndex++) {
    const {filepath, duration, title} = metadatas[fileIndex]
    const endTimeMs = startTimeMs + duration * 1000

    chapters.push({
      elementID: `ch${fileIndex}`,
      startTimeMs,
      endTimeMs,
      tags: {title},
    })

    startTimeMs = endTimeMs
  }

  const tags = {
    title,
    album: title,
    genre: 'Audiobook',

    image: path.join(base, 'art.jpg'),
    chapter: chapters,
    ...specifiedTags,
  }
  const result = NodeID3.write(tags, outputFilepath)
  if (result !== true) {
    throw result
  }
}

function execShellCommand(cmd) {
  const exec = require('child_process').exec
  return new Promise((resolve, reject) => {
    exec(cmd, {shell: '/bin/zsh'}, (error, stdout, stderr) => {
      if (error) return reject(error)
      else resolve(stdout ? stdout : stderr)
    })
  })
}

package.json

{
  "name": "book-stitcher",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "keywords": [],
  "author": "Kent C. Dodds <me@kentcdodds.com> (https://kentcdodds.com/)",
  "license": "MIT",
  "bin": "./bin.js",
  "dependencies": {
    "music-metadata": "^7.5.0",
    "node-id3": "^0.2.1"
  }
}

It seems to require a path without spaces in it (even with quote marks) - otherwise, it throws an FFmpeg error.

[concat @ 0x7f9317804480] No files to concat
/dev/fd/12: Invalid data found when processing input

However, while it concatenated the mp3 files (using a spaceless pathname) and the result contained the metadata and cover art unfortunately it doesn't include a chapter list in the mp3 😞