title: add an image as water mark for video with opacity size adjustment and opacity
body: <p>I'm trying to add watermark for video but as any video editor I also want options of all opacity size and position I found for both opacity and position the below command does it but I missing with scaling the image</p>
  <pre><code>ffmpeg -i test.mp4 -i test1.png -filter_complex &quot;[1]format=rgba,colorchannelmixer=aa=0.25[logo];[0][logo]overlay=50:50&quot; -c:a copy output.mp4
  </code></pre>