[postprocessor:metadata] add 'private' option

docs/configuration.rst

@@ -3768,6 +3768,17 @@ Description
     See the ``mode`` parameter of |open()|_ for further details.
 
 
+metadata.private
+----------------
+Type
+    ``bool``
+Default
+    ``false``
+Description
+    Include private fields,
+    i.e. fields whose name starts with an underscore.
+
+
 metadata.encoding
 -----------------
 Type

gallery_dl/postprocessor/metadata.py

@@ -108,6 +108,7 @@ class MetadataPP(PostProcessor):
         self.mtime = options.get("mtime")
         self.omode = options.get("open", omode)
         self.encoding = options.get("encoding", "utf-8")
+        self.private = options.get("private", False)
 
     def run(self, pathfmt):
         archive = self.archive
@@ -209,7 +210,9 @@ class MetadataPP(PostProcessor):
         fp.write("\n".join(tags) + "\n")
 
     def _write_json(self, fp, kwdict):
-        util.dump_json(util.filter_dict(kwdict), fp, self.ascii, self.indent)
+        if not self.private:
+            kwdict = util.filter_dict(kwdict)
+        util.dump_json(kwdict, fp, self.ascii, self.indent)
 
 
 __postprocessor__ = MetadataPP