anchor.diff:  { stdenv, fetchurl, config, pkgconfig, yasm, zlib, bzip2, alsaLib, texinfo, perl
  -, lame, speex, libtheora, libvorbis, libvpx, x264, xvidcore, libopus
  +, lame, speex, libass, libtheora, libvorbis, libvpx, x264, xvidcore, libopus
   , libvdpau, libva, faac, libdc1394, libXext, libXfixes, SDL
   , freetype, fontconfig, fdk_aac, gnutls
   }:
  
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:     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;
  