anchor.diff:    ];
   
     buildInputs = [
  +    gstreamer
       gst-plugins-base
       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: , ninja
  , pkg-config
  , python3
  , gstreamer
  , gst-plugins-base
  , gettext
  , libav
  