anchor.diff:    python2, pkgconfig, yasm, harfbuzz, zlib,
     autoconf, automake, cmake, libtool, m4, jansson,
     libass, libiconv, libsamplerate, fribidi, libxml2, bzip2,
  -  libogg, libopus, libtheora, libvorbis, libdvdcss, a52dec, fdk_aac,
  +  libogg, libopus, libtheora, libvorbis, libdvdcss, a52dec,
     lame, ffmpeg, libdvdread, libdvdnav, libbluray,
     mp4v2, mpeg2dec, x264, x265, libmkv,
     fontconfig, freetype, hicolor-icon-theme,
     glib, gtk3, intltool, libnotify,
     gst_all_1, dbus-glib, udev, libgudev, libvpx,
  -  useGtk ? true, wrapGAppsHook ? null, libappindicator-gtk3 ? null
  +  useGtk ? true, wrapGAppsHook ? null, libappindicator-gtk3 ? null, useFdk ? false, fdk_aac ? null
   }:
   
   stdenv.mkDerivation rec {
  
positive.code:   buildInputs = [
      fribidi fontconfig freetype jansson zlib
      libass libiconv libsamplerate libxml2 bzip2
      libogg libopus libtheora libvorbis libdvdcss a52dec libmkv fdk_aac
      lame ffmpeg libdvdread libdvdnav libbluray mp4v2 mpeg2dec x264 x265 libvpx
    ] ++ (lib.optionals useGtk [
      glib gtk3 libappindicator-gtk3 libnotify
      gst_all_1.gstreamer gst_all_1.gst-plugins-base dbus-glib udev
      libgudev
    ]);
  
    dontUseCmakeConfigure = true;
  
  
negative.code:   configureFlags = [
      "--disable-df-fetch"
      "--disable-df-verify"
      (if useGtk then "--disable-gtk-update-checks" else "--disable-gtk")
      (if useFdk then "--enable-fdk-aac"            else "")
    ];
  
    NIX_LDFLAGS = [
  