title: ffmpeg drawbox on a given frame
body: <p>I have thousands of rectangle boxes to add in a video. Right now I am using this command:</p>
  
  <pre><code>ffmpeg.exe -i small.ts -vf drawbox=10:10:50:50:red,drawbox=100:100:200:200:green small_with_box.ts
  </code></pre>
  
  <p>However I don't want to add the boxes on an entire frame, but on a given one. Anyone know how can I do that?</p>