title: Capture video from camera on Raspberry Pi and filter in OpenGL before encoding
body: <p>I would like a way to capture video from the camera interface in Raspberry Pi, run it through a filter written as OpenGL shaders, and then send it to the hardware encoder. </p>
  
  <p><a href="http://timgover.blogspot.co.uk/2013/11/yuv-textures.html" rel="noreferrer">This blog post</a> talks about applying OpenGL shader filters onto the output of the camera when using raspistill.  This is the corresponding <a href="https://github.com/raspberrypi/userland/commit/d2c9f912da389c23ed27e81e940be3540f64fc59" rel="noreferrer">source code</a>.  The output in that case however does not go to the video encoder, and this is not running on video, only on stills.  Also (not completely sure) I think this ties into the preview, see these bits: <code>raspitex_state A pointer to the GL preview state</code> and <code>state-&gt;ops.redraw = sobel_redraw</code>.  </p>
  
  <p>The blog also talks about "fastpath", can someone explan what that means in this context?</p>