[realbooru] fix videos and provide fallback URLs (#2530)

revert acc94ac187.

gallery_dl/extractor/gelbooru_v02.py

@@ -25,7 +25,7 @@ class GelbooruV02Extractor(booru.BooruExtractor):
         self.api_root = self.config_instance("api_root") or self.root
 
         if self.category == "realbooru":
-            self._file_url = self._file_url_realbooru
+            self.items = self._items_realbooru
             self._tags = self._tags_realbooru
 
     def _api_request(self, params):
@@ -124,6 +124,35 @@ class GelbooruV02Extractor(booru.BooruExtractor):
                 self.root, md5[0:2], md5[2:4], md5, url.rpartition(".")[2])
         return url
 
+    def _items_realbooru(self):
+        from .common import Message
+        data = self.metadata()
+
+        for post in self.posts():
+            try:
+                html = self._html(post)
+                fallback = post["file_url"]
+                url = post["file_url"] = text.rextract(
+                    html, 'href="', '"', html.index(">Original<"))[0]
+            except Exception:
+                self.log.debug("Unable to fetch download URL for post %s "
+                               "(md5: %s)", post.get("id"), post.get("md5"))
+                continue
+
+            text.nameext_from_url(url, post)
+            post.update(data)
+            self._prepare(post)
+            self._tags(post, html)
+
+            path = url.rpartition("/")[0]
+            post["_fallback"] = (
+                "{}/{}.{}".format(path, post["md5"], post["extension"]),
+                fallback,
+            )
+
+            yield Message.Directory, post
+            yield Message.Url, url, post
+
     def _tags_realbooru(self, post, page):
         tag_container = text.extr(page, 'id="tagLink"', '</div>')
         tags = collections.defaultdict(list)