title: OpenCV output on V4l2
body: <p>I wanted to know if I can use "opencv" to write on a v4l2 device.
  I would take a picture, apply small changes with the features of opencv, and then send it on a v4l2 device.</p>
  
  <p>I searched on the web, but there are a lot of examples on how to read from a V4L2 device, but I found nothing about writing on v4l2.</p>
  
  <p>can someone help me?</p>