anchor.diff:      sha256 = "153kfk8rzrfxx930rrk417b2m695dvy47v4hci3nd49iggx9jzz1";
     };
   
  +  subtitleSupport = config.ffmpeg.subtitle or true;
     mp3Support = config.ffmpeg.mp3 or true;
     speexSupport = config.ffmpeg.speex or true;
     theoraSupport = config.ffmpeg.theora or true;
  
positive.code:     "--enable-avresample"
      "--enable-runtime-cpudetect"
    ]
      ++ stdenv.lib.optional mp3Support "--enable-libmp3lame"
      ++ stdenv.lib.optional speexSupport "--enable-libspeex"
      ++ stdenv.lib.optional theoraSupport "--enable-libtheora"
  
negative.code:     ++ stdenv.lib.optional gnutlsSupport "--enable-gnutls";
  
    buildInputs = [ pkgconfig lame yasm zlib bzip2 alsaLib texinfo perl ]
      ++ stdenv.lib.optional subtitleSupport libass
      ++ stdenv.lib.optional mp3Support lame
      ++ stdenv.lib.optional speexSupport speex
      ++ stdenv.lib.optional theoraSupport libtheora
  