index.js

const { execSync } = require('child_process');
const path = require('path');
const fs = require('fs');

// Path to the input file passed as a command-line argument.
const inputFile = process.argv[2];

/**
 * Extracts chapter information from the given file using ffprobe.
 * @param {string} filePath - The path of the input media file.
 * @returns {Array} - An array of chapter objects.
 */
const getChapters = (filePath) => {
  const command = `ffprobe -i "${filePath}" -show_chapters -loglevel error -print_format json`;
  const output = execSync(command);
  return JSON.parse(output).chapters || [];
};

/**
 * Sanitizes a string by removing invalid characters for filenames.
 * @param {string} name - The original string to sanitize.
 * @returns {string} - The sanitized string.
 */
const sanitizeFileName = (name) => name.replace(/[:\\/*?"<>|]/g, '');

/**
 * Converts a specific chapter to an MP3 file using ffmpeg.
 * @param {string} input - The path of the input media file.
 * @param {object} chapter - The chapter object containing start and end times.
 * @param {string} outputDir - The directory where the output MP3 file will be saved.
 */
const convertChapter = (input, chapter, outputDir) => {
  const title = chapter.tags.title ? sanitizeFileName(chapter.tags.title) : `chapter_${chapter.start_time}`;
  const outputFile = path.join(outputDir, `${title}.mp3`);
  const start = chapter.start_time;
  const duration = chapter.end_time - chapter.start_time;

  const command = `ffmpeg -i "${input}" -ss ${start} -t ${duration} -acodec libmp3lame "${outputFile}"`;
  execSync(command, { stdio: 'inherit' });
  console.log(`Chapter converted: ${outputFile}`);
};

/**
 * Main function to orchestrate the conversion process.
 * It checks the existence of the input file, creates an output directory,
 * and converts either all chapters or the entire file.
 */
const main = () => {
  // Check if the input file exists.
  if (!fs.existsSync(inputFile)) {
    console.error('File not found.');
    process.exit(1);
  }

  // Prepare the output directory based on the input file name.
  const inputFileName = path.basename(inputFile, path.extname(inputFile));
  const outputDir = path.join(path.dirname(inputFile), sanitizeFileName(inputFileName));

  // Create the output directory if it doesn't exist.
  if (!fs.existsSync(outputDir)) {
    fs.mkdirSync(outputDir, { recursive: true });
  }

  // Get chapter information from the input file.
  const chapters = getChapters(inputFile);

  if (chapters.length === 0) {
    // If no chapters are found, convert the entire file to MP3.
    console.log('No chapters found, converting the entire file...');
    const outputFile = path.join(outputDir, `${sanitizeFileName(inputFileName)}.mp3`);
    execSync(`ffmpeg -i "${inputFile}" -acodec libmp3lame "${outputFile}"`, { stdio: 'inherit' });
    console.log(`Conversion completed: ${outputFile}`);
  } else {
    // Convert each chapter individually.
    console.log(`Found ${chapters.length} chapters, converting...`);
    chapters.forEach((chapter) => convertChapter(inputFile, chapter, outputDir));
  }
};

// Execute the main function.
main();