anchor.diff:      (enableFeature (libvorbis != null) "libvorbis")
       (enableFeature (libvpx != null) "libvpx")
       (enableFeature (libwebp != null) "libwebp")
  -    (enableFeature (libX11 != null && libXv != null) "xlib")
  +    (enableFeature (libX11 != null && libXv != null && libXext != null) "xlib")
       (enableFeature (libxcb != null) "libxcb")
       (enableFeature libxcbshmExtlib "libxcb-shm")
       (enableFeature libxcbxfixesExtlib "libxcb-xfixes")
  
positive.code:     bzip2 celt fontconfig freetype frei0r fribidi game-music-emu gnutls gsm
      libjack2 ladspaH lame libaom libass libbluray libbs2b libcaca libdc1394 libmodplug libmysofa
      libogg libopus libssh libtheora libvdpau libvorbis libvpx libwebp libX11
      libxcb libXv lzma openal openjpeg libpulseaudio rtmpdump opencore-amr
      samba SDL2 soxr speex vid-stab vo-amrwbenc wavpack x264 x265 xavs xvidcore
      zeromq4 zlib
    ] ++ optional openglExtlib libGLU_combined
  
negative.code: , libxcbxfixesExtlib ? true # X11 grabbing mouse rendering
  , libxcbshapeExtlib ? true # X11 grabbing shape rendering
  , libXv ? null # Xlib support
  , libXext ? null # Xlib support
  , lzma ? null # xz-utils
  , nvenc ? false, nvidia-video-sdk ? null # NVIDIA NVENC support
  , callPackage # needed for NVENC to access external ffmpeg nvidia headers
  