anchor.diff:    buildInputs = [
       zimg libass
       (python3.withPackages (ps: with ps; [ sphinx cython ]))
  -  ] ++ optionals stdenv.isDarwin [ libiconv ApplicationServices ]
  -    ++ optional ocrSupport   tesseract
  -    ++ optional imwriSupport imagemagick;
  -
  -  configureFlags = [
  -    (optionalString (!ocrSupport)   "--disable-ocr")
  -    (optionalString (!imwriSupport) "--disable-imwri")
  -  ];
  +  ] ++ optionals stdenv.isDarwin [ libiconv ApplicationServices ];
   
     enableParallelBuilding = true;
   
  
positive.code:   postInstall = ''
      wrapProgram $out/bin/vspipe \
          --prefix PYTHONPATH : $out/${python3.sitePackages}
    '';
  
    meta = with lib; {
  
negative.code: , runCommandCC, runCommand, vapoursynth, writeText, patchelf, buildEnv
  , zimg, libass, python3, libiconv
  , ApplicationServices
  }:
  
  with lib;
  