title: FFMpeg multiple actions with the same filter_complex
body: <p>I'm working with 2 videos and I want to make 3 different operations at same 
  execution with FFmpeg. Each command works separate but it'll much more efficient to make them all run at the same execution.</p>
  
  <p>So for example I have:</p>
  
  <p><strong>Video 1</strong></p>
  
  <p><strong>Video 2</strong></p>
  
  <p>First I want to cut both videos from starting point to end point:</p>
  
  <pre><code>cmd = -i video1Path -ss 00:00:30.0 -c copy -t 00:00:10.0 video1Output
  cmd = -i video2Path -ss 00:00:30.0 -c copy -t 00:00:10.0 video2Output
  </code></pre>
  
  <p>Than resizing <strong>Video 1</strong>:</p>
  
  <pre><code>cmd = "-i " + video1Output+ " -vf scale=240:360" + resizedVideo1;
  </code></pre>
  
  <p>Now overlaying the <strong>resizedVideo1</strong> on top of <strong>Video 2</strong>:</p>
  
  <pre><code>cmd = "-i " + video2Output + " -i " + resizedVideo1 + " -filter_complex [0:v][1:v]" + overlayCmd + " " + finalVideoPath;
  </code></pre>
  
  <p>I'm wondering if it's possible to achieve all this actions at the same FFMpeg executions using 1 filter_complex...</p>