anchor.diff:      ++ optional vdpauSupport       libvdpau
       ++ optional speexSupport       speex
       ++ optional bs2bSupport        libbs2b
  +    ++ optional openalSupport      openalSoft
  +    ++ optional (openalSupport && stdenv.isDarwin) darwin.apple_sdk.frameworks.OpenAL
       ++ optional libpngSupport      libpng
       ++ optional youtubeSupport     youtube-dl
       ++ optional sdl2Support        SDL2
  
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")
  