anchor.diff:      "--enable-gpl"
       "--enable-postproc"
       "--enable-swscale"
  -    "--disable-ffplay"
       "--enable-shared"
       "--enable-avresample"
       "--enable-runtime-cpudetect"
  
positive.code:     ++ stdenv.lib.optional vdpauSupport "--enable-vdpau"
      ++ stdenv.lib.optional faacSupport "--enable-libfaac --enable-nonfree"
      ++ stdenv.lib.optional dc1394Support "--enable-libdc1394"
      ++ stdenv.lib.optional x11grabSupport "--enable-x11grab";
  
    buildInputs = [ pkgconfig lame yasm zlib bzip2 alsaLib ]
      ++ stdenv.lib.optional mp3Support lame
  
negative.code: , faacSupport ? false, faac ? null
  , dc1394Support ? false, libdc1394 ? null
  , x11grabSupport ? false, libXext ? null, libXfixes ? null
  , playSupport ? true, SDL ? null
  }:
  
  assert speexSupport -> speex != null;
  