title: Place FFMPEG videos side by side, allign by frame number
body: <p>So, I have 2 videos I would like to place side by side. I would like to align them by a frame number that I know for each video, assuming both videos have the same FPS. The frame numbers were found using the following command.</p>
  
  <pre><code>ffmpeg -i "input.mp4" "output/%08d.jpg"
  </code></pre>
  
  <p>So, let's say I know the frame number I want to align for Video A is 126, while for Video B the frame number is 179. I want to align the videos side by side with these two frames lining up, so that the resulting video would be displaying Video A frame 126 at the same time as Video B frame 179. The resulting video also shouldn't have any pieces from either video removed, so if one of the videos hasn't started or isn't finished, the resulting video keeps playing the active video, rather than having only the times when both videos are supposed to be playing. I also want to align both audio tracks as well.</p>
  
  <p>For this question I would prefer a single-command solution where I only need to input the videos and frame numbers I want to align, rather than having to do several steps manually.</p>