anchor.diff:  assert avformatLibrary ->
     avcodecLibrary
     && avutilLibrary;
  -assert avresampleLibrary -> avutilLibrary;
   assert postprocLibrary -> avutilLibrary;
   assert swresampleLibrary -> soxr != null;
   assert swscaleLibrary -> avutilLibrary;
  
positive.code:     "--${boolEn avdeviceLibrary}-avdevice"
      "--${boolEn avfilterLibrary}-avfilter"
      "--${boolEn avformatLibrary}-avformat"
      "--${boolEn avresampleLibrary}-avresample"
      "--${boolEn avutilLibrary}-avutil"
      "--${boolEn (postprocLibrary && gplLicensing)}-postproc"
      "--${boolEn swresampleLibrary}-swresample"
  
negative.code:     };
      "9.9" = { # Git
        fetchzipversion = 5;
        version = "2018.01.08";
        rev = "ed03fad2cc523480a7ec385fb3e9bf876769acce";
        sha256 = "722809dfde1e91ce0e49577dd0c1ac2046eb567bc22a8c8d1bd8b46766b27939";
      };
    };
    source = sources."${channel}";
  