title: ffmpeg fix watermark size or percentage
body: <p>i have some videos and i want to add watermark to them
  but problem is coz in every video "watermark size" is different
   (in some videos watermark is smaller and in some is bigger - i think because of video input size coz its different)</p>
  
  <p>here is my ffmpeg command (just link is different)</p>
  
  <pre><code>ffmpeg -i "http://VIDEO-LINK" -i "/var/www/logo/logo.png" -filter_complex 'overlay=17:17' -vcodec h264 -crf 25 -preset veryfast -maxrate 600k -bufsize 600k -aspect '640:360' -s '640:360' -acodec libfdk_aac -hls_time 10 -hls_wrap 10 -start_number 1 -y "1.m3u8"
  </code></pre>
  
  <p>is there a way to make any percentage or fixed watermark based on output which is 640x360</p>
  
  <p>coz if input video is 640x360 it show big watermark with this command 
  if input link is 1280x720 then watermark is so small</p>