ffmpeg: overlay a png image on a video with custom transparency? : <p>Suppose I have a video <code>foo.mkv</code> and an image <code>bar.png</code> (which happens to contains an alpha channel). I can blend this image over the video like this:</p>

<pre><code>ffmpeg 
 -i foo.mkv 
 -i bar.png 
 -filter_complex "[0:v][1:v]overlay" 
 -vcodec libx264 
 myresult.mkv
</code></pre>

<p>(using multiple lines here for readability, normally this is one command line).</p>

<p>Now, besides the png image having an alpha channel of its own, I would also apply a custom <em>overall transparency</em> when blending this image over the video.</p>

<p>In the above example, the image would be visible 100% on top of the video — or at least the parts where its alpha channel is fully opaque.</p>

<p>Is there a way to add a custom overall opacity or transparency blend factor, something like <code>opacity=0.5</code> or whatever, which would make the image only 50% visible?</p>
