title: Creating a ROS bag file out of a mp4 video
body: <p>I have a .mp4 format video and want to create a bag file out of it to use for ORB_SLAM2. I know that need to publish my video to a topic. Once my video is being published need to record the video topic. Im using Ubuntu 16.04 and ROS kinetic. </p>
  
  <p>I already create the image_transport package and the publisher node. Also build it. Its working but I need to publish a video stream topic not single image. There is tutorial code "Adding video stream from a webcam" but I already have the video steam. So any help regarding this?</p>