anchor.diff:    available = x: x != null;
   
     sound =
  -    if enableFFmpeg    then "ffmpeg" else
  -    if enableGstreamer then "gst"    else "none";
  +    if enableFFmpeg then "ffmpeg" else "none";
   
     renderers = []
       ++ optional enableAGG    "agg"
  
positive.code: 
  # media
  , enableFFmpeg    ? true,  ffmpeg_2 ? null
  , enableGstreamer ? false, gst-plugins-base ? null
                           , gst-plugins-ugly ? null
                           , gst-ffmpeg ? null
  
  # misc
  , enableJemalloc ? true, jemalloc  ? null
  
negative.code:     ++ optional  enableJemalloc  jemalloc
      ++ optional  enableHwAccel   libGLU_combined
      ++ optionals enablePlugins   [ xulrunner npapi_sdk ]
      ++ optionals enableGTK       [ gtk2 gnome2.gtkglext gnome2.GConf ];
  
    configureFlags = with stdenv.lib; [
      "--with-boost-incl=${boost.dev}/include"
  