anchor.diff:   *   aacplus avisynth cdio-paranoia crystalhd libavc1394 libiec61883
    *   libmxf libnut libquvi nvenc opencl opencore-amr openh264 oss shine twolame
    *   utvideo vo-aacenc vo-amrwbenc xvmc zvbi blackmagic-design-desktop-video
  - *
  - * Need fixes to support Darwin:
  - *   frei0r, game-music-emu, gsm, libjack2, libssh, libvpx(stable 1.3.0), openal, openjpeg_1,
  - *   pulseaudio, rtmpdump, samba, vid-stab, wavpack, x265. xavs
    *
    * Not supported:
    *   stagefright-h264(android only)
  
positive.code:  */
  
  let
    inherit (stdenv) isCygwin isFreeBSD isLinux;
    inherit (stdenv.lib) optional optionals enableFeature;
  in
  
  
negative.code: #, vo-aacenc ? null # AAC encoder
  #, vo-amrwbenc ? null # AMR-WB encoder
  , wavpack ? null # Wavpack encoder
  , x11grabExtlib ? false
  , x264 ? null # H.264/AVC encoder
  , x265 ? null # H.265/HEVC encoder
  , xavs ? null # AVS encoder
  