video-stream.js

app.get('/stream', (req, res) => {
  const pathToVideo = "/path/to/video";
  fs.stat(pathToVideo, function(err, stats) {
      if (err) {
        if (err.code === 'ENOENT') {
          // 404 Error if file not found
          console.log('File not found!');
          return res.sendStatus(404);
        }
        res.end(err);
      }
      const range = req.headers.range;
      if (!range) {
       // 416 Wrong range
       return res.sendStatus(416);
      }
      const positions = range.replace(/bytes=/, "").split("-");
      const start = parseInt(positions[0], 10);
      const total = stats.size;
      const end = positions[1] ? parseInt(positions[1], 10) : total - 1;
      const chunksize = (end - start) + 1;

      res.writeHead(206, {
        "Content-Range": "bytes " + start + "-" + end + "/" + total,
        "Accept-Ranges": "bytes",
        "Content-Length": chunksize,
        "Content-Type": "video/mkv"
      });

      const stream = fs.createReadStream(pathToVideo, { start: start, end: end })
        .on("open", function() {
          stream.pipe(res);
        }).on("error", function(err) {
          res.end(err);
        });
    });
});