[vk] Add support for sibnet embeds (closes ytdl-org#9500)

youtube_dl/extractor/vk.py

@@ -300,6 +300,13 @@ class VKIE(VKBaseIE):
             'only_matching': True,
         }]
 
+    @staticmethod
+    def _extract_sibnet_urls(webpage):
+        # https://help.sibnet.ru/?sibnet_video_embed
+        return [unescapeHTML(mobj.group('url')) for mobj in re.finditer(
+            r'<iframe\b[^>]+\bsrc=(["\'])(?P<url>(?:https?:)?//video\.sibnet\.ru/shell\.php\?.*?\bvideoid=\d+.*?)\1',
+            webpage)]
+
     def _real_extract(self, url):
         mobj = re.match(self._VALID_URL, url)
         video_id = mobj.group('videoid')
@@ -408,6 +415,10 @@ def _real_extract(self, url):
         if odnoklassniki_url:
             return self.url_result(odnoklassniki_url, OdnoklassnikiIE.ie_key())
 
+        sibnet_urls = self._extract_sibnet_urls(info_page)
+        if sibnet_urls:
+            return self.url_result(sibnet_urls[0])
+
         m_opts = re.search(r'(?s)var\s+opts\s*=\s*({.+?});', info_page)
         if m_opts:
             m_opts_url = re.search(r"url\s*:\s*'((?!/\b)[^']+)", m_opts.group(1))