lrc2srt.js

const rl = require('readline').createInterface({
  input: process.stdin,
  output: process.stdout,
  terminal: false,
});

const data = [];

rl.on('line', (line) => {
  data.push(line);
});

rl.on('close', () => {
  console.log(handleData(data));
});

const regex = /^\[(\d{2}):(\d{2})(\.\d{2})?\](.*)$/;

/** @param {string[]} data */
function handleData(data) {
  const d = [];
  data.forEach((line = '') => {
    const match = regex.exec(line);
    if (match) {
      const [_, mm, ss, xx = '00', txt = ''] = match;
      d.push({ t: `00:${mm}:${ss},${xx.padStart(3, '0')}`, txt });
    }
  });
  return d
    .map(
      ({ t, txt }, idx) => `${idx}
${t} --> ${d[idx + 1]?.t ?? '01:00:00,000'}
${txt}`
    )
    .join('\n\n');
}