castnow: wrap with ffmpeg

Required for --tomp4.

pkgs/development/node-packages/overrides.nix

@@ -137,6 +137,15 @@ final: prev: {
     meta = oldAttrs.meta // { broken = since "12"; };
   });
 
+  castnow = prev.castnow.override {
+    nativeBuildInputs = [ pkgs.makeWrapper ];
+
+    postInstall = ''
+      wrapProgram "$out/bin/castnow" \
+          --prefix PATH : ${pkgs.lib.makeBinPath [ pkgs.ffmpeg ]}
+    '';
+  };
+
   eask = prev."@emacs-eask/cli".override {
     name = "eask";
   };