Delay ASS subtitles by certain seconds.

delay_ass.js

// USAGE:
// node delay_ass.js subtitle.ass -32

const fs = require('fs');
const fileName = process.argv[2];
const delaySeconds = process.argv[3];
const encoding = process.argv[4] || 'utf16le';

if (typeof delaySeconds === 'undefined') {
  console.log(
    'Error: Please provide a number after file name for seconds to delay, e.g.:'
  );
  console.log('$ node delay_ass.js S02E01.ass -12.5');
  return;
}
const isDelay = !delaySeconds.startsWith('-');
const adjective = isDelay ? 'later' : 'earlier';

fs.readFile(fileName, encoding, (err, data) => {
  if (err) return console.log(err);

  const dataLines = data.split(/\n/);
  const newLines = dataLines.map(line => {
    if (line.startsWith('Dialogue:')) {
      return processLine(line);
    } else {
      return line;
    }
  });
  const newData = newLines.join('\n');

  fs.writeFile(fileName, newData, encoding, err => {
    if (err) return console.log(err);
    console.log(
      'Successfully made subtitle appear ',
      adjective,
      'by',
      delaySeconds,
      'seconds.'
    );
  });
});

function processLine(line) {
  const blocks = line.split(/,/);
  const newBlocks = blocks.map((block, i) => {
    if (i === 1 || i === 2) {
      return delayTimestamp(block);
    } else {
      return block;
    }
  });

  return newBlocks.join(',');
}

function delayTimestamp(time, delayStr = delaySeconds) {
  // E.G. 0:14:12.04

  const timeArr = time.split(/:/).map(e => parseFloat(e, 10));
  const [h, m, s] = timeArr;
  const totalS = s + 60 * m + 3600 * h;
  const delay = parseFloat(delayStr, 10);
  const newTotalS = totalS + delay;

  const newH = Math.max(0, Math.floor(newTotalS / 3600));
  const newM = Math.max(0, Math.floor((newTotalS % 3600) / 60));
  const newS = Math.max(0, newTotalS % 60);
  const newTime = [newH, newM, newS.toFixed(2)].join(':');

  return newTime;
}