anchor.diff:  , vdpauSupport ? true, libvdpau ? null
   , faacSupport ? false, faac ? null
   , dc1394Support ? false, libdc1394 ? null
  -, x11grabSupport ? false, libXext ? null, libXfixes ? null
   }:
   
   assert speexSupport -> speex != null;
  
positive.code:     ++ stdenv.lib.optional xvidSupport xvidcore
      ++ stdenv.lib.optional vdpauSupport libvdpau
      ++ stdenv.lib.optional faacSupport faac
      ++ stdenv.lib.optional dc1394Support libdc1394
      ++ stdenv.lib.optionals x11grabSupport [ libXext libXfixes ];
  
    enableParallelBuilding = true;
      
  
negative.code:     ++ stdenv.lib.optional xvidSupport "--enable-libxvid"
      ++ stdenv.lib.optional vdpauSupport "--enable-vdpau"
      ++ stdenv.lib.optional faacSupport "--enable-libfaac --enable-nonfree"
      ++ stdenv.lib.optional dc1394Support "--enable-libdc1394";
  
    buildInputs = [ pkgconfig lame yasm zlib bzip2 ]
      ++ stdenv.lib.optional mp3Support lame
  