anchor.diff:  , x264Support ? false, x264 ? null
   , xvidSupport ? false, xvidcore ? null
   , lameSupport ? true, lame ? null
  +, speexSupport ? true, speex ? null
   , screenSaverSupport ? true, libXScrnSaver
   , pulseSupport ? false, pulseaudio
   , mesa, pkgconfig, unzip, yasm, freefont_ttf
  
positive.code: assert amrSupport -> (amrnb != null && amrwb != null);
  assert screenSaverSupport -> libXScrnSaver != null;
  assert vdpauSupport -> libvdpau != null;
  
  let
  
  
negative.code:     ++ stdenv.lib.optional pulseSupport pulseaudio
      ++ stdenv.lib.optional screenSaverSupport libXScrnSaver
      ++ stdenv.lib.optional lameSupport lame
      ++ stdenv.lib.optional vdpauSupport libvdpau
      ++ stdenv.lib.optional speexSupport speex;
  
    buildNativeInputs = [ yasm ];
  
  