title: Extracting audio from video files
body: <p>I just received a 30 day trial of the Computer Vision System Toolbox, and I just tested it out. I found this code <a href="https://www.quora.com/How-do-I-extract-and-interpret-audio-from-a-video-file-using-MATLAB" rel="nofollow">online</a> that separates video from audio: </p>
  
  <pre><code>file='movie.AVI';
  file1='targetfile.wav';
  
  hmfr= video.MultimediaFileReader(file,'AudioOutputPort',true,'VideoOutputPort',false);
  hmfw = video.MultimediaFileWriter(file1,'AudioInputPort',true,'FileFormat','WAV');
  
  while ~isDone(hmfr)
  audioFrame = step(hmfr);
  step(hmfw,audioFrame);  
  end
  
  close(hmfw);
  close(hmfr);
  </code></pre>
  
  <p>but I can't run it, I only get the error:
   <code>Undefined variable "video" or class "video.MultimediaFileReader".</code>
  I'm not quite sure what this means, does it refer to my code or the computer vision system toolbox? I checked, I have all the requirements and the add-on manager says it's properly installed, so I'm not quite sure why I get this error.</p>