anchor.diff:  }:
   
   assert faacSupport -> faac != null;
  +assert gtkSupport -> gtk3 != null;
   
   let
     inherit (stdenv.lib) optional optionalString;
  
positive.code: { stdenv, fetchurl, pkgconfig, python, gst-plugins-base, orc
  , faacSupport ? false, faac ? null
  , faad2, libass, libkate, libmms
  , libmodplug, mpeg2dec, mpg123
  , openjpeg, libopus, librsvg
  
negative.code: 
    buildInputs = [
      gst-plugins-base orc
      faad2 gtk3 libass libkate libmms
      libmodplug mpeg2dec mpg123
      openjpeg libopus librsvg
      fluidsynth libvdpau
  