code: function () {
    vid2.read(function (err, m2) {
  	if (writer2 === null)
  	  writer2 = new cv.VideoWriter(filename2, 'DIVX', vid2.getFPS(), m2.size(), true);
  
  	x++;
  	writer2.write(m2, function(err){
  	  if (x < 100) {
  		iter();
  	  } else {
  		vid2.release();
  		writer2.release();
  	  }
  	});
  	m2.release();
  	delete m2;
    });
  }
docs: do the same write async