title: Resize video to same size
body: <p>I have a list of video files with different resolutions. And I should to change them to 1920x1080. It's easy to make using ffmpeg and scale filter but result video is wrong aspect ratio. If I use aspect ratio then output resolution isn't fullhd. Is it possible to change resolution to best available like scale="'if(gt(a,16/9),1920,-1)':'if(gt(a,16/9),-1,1080)'"
  and all remaining space is filled in black color ?</p>