anchor.diff:  let
     inherit (builtins)
       compareVersions;
  +
  +  inherit (stdenv)
  +    targetSystem;
  +
     inherit (lib)
       boolEn
  +    elem
       optional
       optionals
       optionalString
  +    platforms
       versionOlder;
   
     sources = {
  
positive.code:     /*
       *  Hardware accelerators
       */
      "--disable-audiotoolbox"  # macos
      "--${boolEn (
        nvidia-cuda-toolkit != null
        && nvidia-drivers != null)}-cuda"
      "--${boolEn (
        nvidia-cuda-toolkit != null
        && nvidia-drivers != null)}-cuvid"
      "--disable-d3d11va"  # windows
      "--disable-dxva2"  # windows
      "--${boolEn (mfx-dispatcher != null)}-libmfx"
      "--${boolEn libnppSupport}-libnpp"
      #"--${boolEn (mmal != null)}-mmal"
      /**/"--disable-mmal"
      "--${boolEn nvenc}-nvenc"
      "--${boolEn (libva != null)}-vaapi"
      "--disable-vda"  # macos
      "--${boolEn (libvdpau != null)}-vdpau"
      "--disable-videotoolbox"  # macos
      # Undocumented
      # FIXME
      #"--${boolEn (xorg.libXvMC != null)}-xvmc"
  
negative.code: , libnppSupport ? false
  , libogg
  , libraw1394
  , librsvg
  , libsndio ? null
  , libssh
  , libtheora
  