anchor.diff:  assert x264Support -> x264 != null;
   assert jackaudioSupport -> jackaudio != null;
   assert pulseSupport -> pulseaudio != null;
  -
  +assert libpngSupport -> libpng != null;
   
   let
   
  
positive.code: , x264Support ? false, x264 ? null
  , jackaudioSupport ? false, jackaudio ? null
  , pulseSupport ? false, pulseaudio ? null
  }:
  
  assert x11Support -> (libX11 != null && libXext != null && mesa != null);
  
negative.code:     ++ optional screenSaverSupport libXScrnSaver
      ++ optional lameSupport lame
      ++ optional vdpauSupport libvdpau
      ++ optional speexSupport speex
      ++ optional libpngSupport libpng
      ;
  
    buildNativeInputs = [ yasm ];
  
  