resume.js

var youtubedl = require('..');
var fs = require('fs');
var output = 'myvideo.mp4';

var downloaded = 0;
if (fs.existsSync(output)) {
  downloaded = fs.statSync(output).size;
}

var video = youtubedl('https://www.youtube.com/watch?v=179MiZSibco',

  // Optional arguments passed to youtube-dl.
  ['--format=18'],

  // start will be sent as a range header
  { start: downloaded, cwd: __dirname });

// Will be called when the download starts.
video.on('info', function(info) {
  console.log('Download started');
  console.log('filename: ' + info._filename);

  // info.size will be the amount to download, add
  var total = info.size + downloaded;
  console.log('size: ' + total);

  if (downloaded > 0) {
    // size will be the amount already downloaded
    console.log('resuming from: ' + downloaded);

    // display the remaining bytes to download
    console.log('remaining bytes: ' + info.size);
  }
});

video.pipe(fs.createWriteStream('myvideo.mp4', { flags: 'a' }));

video.on('end', function() {
  console.log('finished downloading!');
});