anchor.diff:  assert bluraySupport      -> available libbluray;
   assert speexSupport       -> available speex;
   assert theoraSupport      -> available libtheora;
  +assert openalSupport      -> available openalSoft;
   assert pulseSupport       -> available libpulseaudio;
   assert bs2bSupport        -> available libbs2b;
   assert cacaSupport        -> available libcaca;
  
positive.code: , youtubeSupport     ? true,  youtube-dl    ? null
  , vaapiSupport       ? true,  libva         ? null
  , drmSupport         ? true,  libdrm        ? null
  , vapoursynthSupport ? false, vapoursynth   ? null
  , archiveSupport     ? false, libarchive    ? null
  , jackaudioSupport   ? false, libjack2      ? null
  
negative.code:     (enableFeature archiveSupport "libarchive")
      (enableFeature dvdreadSupport "dvdread")
      (enableFeature dvdnavSupport "dvdnav")
      (enableFeature openalSupport "openal")
      (enableFeature vaapiSupport "vaapi")
      (enableFeature waylandSupport "wayland")
      (enableFeature stdenv.isLinux "dvbin")
  