anchor.diff:  , ninja
   , pkg-config
   , python3
  +, gstreamer
   , gst-plugins-base
   , gettext
   , libav
  
positive.code: 
  stdenv.mkDerivation rec {
    pname = "gst-libav";
    version = "1.18.5";
  
    src = fetchurl {
      url = "https://gstreamer.freedesktop.org/src/${pname}/${pname}-${version}.tar.xz";
      sha256 = "sha256-gi4AipEOndE67b3Y3GP+3vQEDA7i6Se6sxEuneaTpUg=";
    };
  
    outputs = [ "out" "dev" ];
  
negative.code:   ];
  
    buildInputs = [
      gstreamer
      gst-plugins-base
      libav
    ];
  