diff --git a/yt_dlp/extractor/youtube.py b/yt_dlp/extractor/youtube.py
index cdf19c4d60..94e113d442 100644
--- a/yt_dlp/extractor/youtube.py
+++ b/yt_dlp/extractor/youtube.py
@@ -131,6 +131,8 @@ def parse_qs(url):
         },
         'INNERTUBE_CONTEXT_CLIENT_NAME': 21,
     },
+    # ios has HLS live streams
+    # See: https://github.com/TeamNewPipe/NewPipeExtractor/issues/680
     'ios': {
         'INNERTUBE_API_KEY': 'AIzaSyAO_FJ2SlqU8Q4STEHLGCilw_Y9_11qcW8',
         'INNERTUBE_CONTEXT': {
@@ -162,6 +164,8 @@ def parse_qs(url):
         },
         'INNERTUBE_CONTEXT_CLIENT_NAME': 26
     },
+    # mweb has 'ultralow' formats
+    # See: https://github.com/yt-dlp/yt-dlp/pull/557
     'mweb': {
         'INNERTUBE_API_KEY': 'AIzaSyDCU8hByM-4DrUqRUYnGn-3llEO78bcxq8',
         'INNERTUBE_CONTEXT': {
@@ -205,23 +209,28 @@ def build_innertube_clients():
 
 class YoutubeBaseInfoExtractor(InfoExtractor):
     """Provide base functions for Youtube extractors"""
+
+    _RESERVED_NAMES = (
+        r'channel|c|user|playlist|watch|w|v|embed|e|watch_popup|'
+        r'shorts|movies|results|shared|hashtag|trending|feed|feeds|'
+        r'browse|oembed|get_video_info|iframe_api|s/player|'
+        r'storefront|oops|index|account|reporthistory|t/terms|about|upload|signin|logout')
+
+    _PLAYLIST_ID_RE = r'(?:(?:PL|LL|EC|UU|FL|RD|UL|TL|PU|OLAK5uy_)[0-9A-Za-z-_]{10,}|RDMM|WL|LL|LM)'
+
+    _NETRC_MACHINE = 'youtube'
+
+    # If True it will raise an error if no login info is provided
+    _LOGIN_REQUIRED = False
+
+    r'''  # Unused since login is broken
     _LOGIN_URL = 'https://accounts.google.com/ServiceLogin'
     _TWOFACTOR_URL = 'https://accounts.google.com/signin/challenge'
 
     _LOOKUP_URL = 'https://accounts.google.com/_/signin/sl/lookup'
     _CHALLENGE_URL = 'https://accounts.google.com/_/signin/sl/challenge'
     _TFA_URL = 'https://accounts.google.com/_/signin/challenge?hl=en&TL={0}'
-
-    _RESERVED_NAMES = (
-        r'channel|c|user|browse|playlist|watch|w|v|embed|e|watch_popup|shorts|'
-        r'movies|results|shared|hashtag|trending|feed|feeds|oembed|get_video_info|'
-        r'storefront|oops|index|account|reporthistory|t/terms|about|upload|signin|logout')
-
-    _NETRC_MACHINE = 'youtube'
-    # If True it will raise an error if no login info is provided
-    _LOGIN_REQUIRED = False
-
-    _PLAYLIST_ID_RE = r'(?:(?:PL|LL|EC|UU|FL|RD|UL|TL|PU|OLAK5uy_)[0-9A-Za-z-_]{10,}|RDMM|WL|LL|LM)'
+    '''
 
     def _login(self):
         """
@@ -460,10 +469,9 @@ def _ytcfg_get_safe(self, ytcfg, getter, expected_type=None, default_client='web
         return _func(ytcfg) or _func(self._get_default_ytcfg(default_client))
 
     def _extract_client_name(self, ytcfg, default_client='web'):
-        return (
-            try_get(ytcfg, lambda x: x['INNERTUBE_CLIENT_NAME'], compat_str)
-            or self._ytcfg_get_safe(
-                ytcfg, lambda x: x['INNERTUBE_CONTEXT']['client']['clientName'], compat_str, default_client))
+        return self._ytcfg_get_safe(
+            ytcfg, (lambda x: x['INNERTUBE_CLIENT_NAME'],
+                    lambda x: x['INNERTUBE_CONTEXT']['client']['clientName']), compat_str, default_client)
 
     @staticmethod
     def _extract_session_index(*data):
@@ -473,10 +481,9 @@ def _extract_session_index(*data):
                 return session_index
 
     def _extract_client_version(self, ytcfg, default_client='web'):
-        return (
-            try_get(ytcfg, lambda x: x['INNERTUBE_CLIENT_VERSION'], compat_str)
-            or self._ytcfg_get_safe(
-                ytcfg, lambda x: x['INNERTUBE_CONTEXT']['client']['clientVersion'], compat_str, default_client))
+        return self._ytcfg_get_safe(
+            ytcfg, (lambda x: x['INNERTUBE_CLIENT_VERSION'],
+                    lambda x: x['INNERTUBE_CONTEXT']['client']['clientVersion']), compat_str, default_client)
 
     def _extract_api_key(self, ytcfg=None, default_client='web'):
         return self._ytcfg_get_safe(ytcfg, lambda x: x['INNERTUBE_API_KEY'], compat_str, default_client)
@@ -1181,7 +1188,8 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
             'info_dict': {
                 'id': 'Tq92D6wQ1mg',
                 'title': '[MMD] Adios - EVERGLOW [+Motion DL]',
-                'ext': 'mp4','upload_date': '20191227',
+                'ext': 'mp4',
+                'upload_date': '20191227',
                 'uploader_id': 'UC1yoRdFoFJaCY-AGfD9W0wQ',
                 'uploader': 'Projekt Melody',
                 'description': 'md5:17eccca93a786d51bc67646756894066',
@@ -2741,8 +2749,8 @@ def feed_entry(name):
         for f in formats:
             if '&c=WEB&' in f['url'] and '&ratebypass=yes&' not in f['url']:  # throttled
                 f['source_preference'] = -10
-                note = f.get('format_note')
-                f['format_note'] = f'{note} (throttled)' if note else '(throttled)'
+                # TODO: this method is not reliable
+                f['format_note'] = format_field(f, 'format_note', '%s ') + '(maybe throttled)'
 
         # Source is given priority since formats that throttle are given lower source_preference
         # When throttling issue is fully fixed, remove this