title: Merge/Blend/Composite transparent webm files with a jpg/png using ffmpeg
body: <p>I previously had generated color.webm and alpha.webm files withffmpeg using png images.
  However, when I play the generated videos in my application it consumes quite some resources so I have decided to create a standard video(No alpha needed), I cannot re-record the videos as there are a lot of them at this point.</p>
  <p>I am generating the alpha and color video using the following command <code>ffmpeg -framerate 30 -i img%d.png -filter_complex &quot;alphaextract[a]&quot; -map 0:v -c:v libvpx-vp9 -pix_fmt yuv420p -auto-alt-ref 0 -crf 15 -b:v 0 color.webm -map &quot;[a]&quot; -c:v libvpx-vp9 -pix_fmt yuv420p -auto-alt-ref 0 -crf 15 -b:v 0 alpha.webm</code></p>
  <p>I am looking to get a final video output where in alpha values are replaced with the png/jpg image, it's more like replacing the green screen with a background however in my case greenscreen is the alpha channel.</p>
  <p><strong>Could any one let me know how to combine alpha.webm, color.webm with a jpg/png image without minimal or no quality loss?
  .</strong></p>