diff --git a/devscripts/lazy_load_template.py b/devscripts/lazy_load_template.py
index 626b85d620..c8815e01bc 100644
--- a/devscripts/lazy_load_template.py
+++ b/devscripts/lazy_load_template.py
@@ -10,7 +10,7 @@
 )
 
 # These bloat the lazy_extractors, so allow them to passthrough silently
-ALLOWED_CLASSMETHODS = {'get_testcases', 'extract_from_webpage'}
+ALLOWED_CLASSMETHODS = {'extract_from_webpage', 'get_testcases', 'get_webpage_testcases'}
 _WARNED = False
 
 
diff --git a/devscripts/make_lazy_extractors.py b/devscripts/make_lazy_extractors.py
index 2d4530eb96..c502bdf896 100644
--- a/devscripts/make_lazy_extractors.py
+++ b/devscripts/make_lazy_extractors.py
@@ -14,10 +14,17 @@
 
 NO_ATTR = object()
 STATIC_CLASS_PROPERTIES = [
-    'IE_NAME', 'IE_DESC', 'SEARCH_KEY', '_VALID_URL', '_WORKING', '_ENABLED', '_NETRC_MACHINE', 'age_limit'
+    'IE_NAME', '_ENABLED', '_VALID_URL',  # Used for URL matching
+    '_WORKING', 'IE_DESC', '_NETRC_MACHINE', 'SEARCH_KEY',  # Used for --extractor-descriptions
+    'age_limit',  # Used for --age-limit (evaluated)
+    '_RETURN_TYPE',  # Accessed in CLI only with instance (evaluated)
 ]
 CLASS_METHODS = [
-    'ie_key', 'working', 'description', 'suitable', '_match_valid_url', '_match_id', 'get_temp_id', 'is_suitable'
+    'ie_key', 'suitable', '_match_valid_url',  # Used for URL matching
+    'working', 'get_temp_id', '_match_id',  # Accessed just before instance creation
+    'description',  # Used for --extractor-descriptions
+    'is_suitable',  # Used for --age-limit
+    'supports_login', 'is_single_video',  # Accessed in CLI only with instance
 ]
 IE_TEMPLATE = '''
 class {name}({bases}):
diff --git a/test/parameters.json b/test/parameters.json
index bc45613741..8789ce14b3 100644
--- a/test/parameters.json
+++ b/test/parameters.json
@@ -44,5 +44,6 @@
     "writesubtitles": false,
     "allsubtitles": false,
     "listsubtitles": false,
-    "fixup": "never"
+    "fixup": "never",
+    "allow_playlist_files": false
 }
diff --git a/yt_dlp/YoutubeDL.py b/yt_dlp/YoutubeDL.py
index 525d3ab6e5..20940085e8 100644
--- a/yt_dlp/YoutubeDL.py
+++ b/yt_dlp/YoutubeDL.py
@@ -1357,7 +1357,7 @@ def prepare_filename(self, info_dict, dir_type='', *, outtmpl=None, warn=False):
         return self.get_output_path(dir_type, filename)
 
     def _match_entry(self, info_dict, incomplete=False, silent=False):
-        """ Returns None if the file should be downloaded """
+        """Returns None if the file should be downloaded"""
         _type = info_dict.get('_type', 'video')
         assert incomplete or _type == 'video', 'Only video result can be considered complete'
 
@@ -1381,6 +1381,7 @@ def check_filter():
                 if rejecttitle:
                     if re.search(rejecttitle, title, re.IGNORECASE):
                         return '"' + title + '" title matched reject pattern "' + rejecttitle + '"'
+
             date = info_dict.get('upload_date')
             if date is not None:
                 dateRange = self.params.get('daterange', DateRange())
@@ -2953,8 +2954,6 @@ def process_info(self, info_dict):
         if 'format' not in info_dict and 'ext' in info_dict:
             info_dict['format'] = info_dict['ext']
 
-        # This is mostly just for backward compatibility of process_info
-        # As a side-effect, this allows for format-specific filters
         if self._match_entry(info_dict) is not None:
             info_dict['__write_download_archive'] = 'ignore'
             return
diff --git a/yt_dlp/extractor/adobepass.py b/yt_dlp/extractor/adobepass.py
index ec1be008a3..e5944f7146 100644
--- a/yt_dlp/extractor/adobepass.py
+++ b/yt_dlp/extractor/adobepass.py
@@ -1352,7 +1352,7 @@
 }
 
 
-class AdobePassIE(InfoExtractor):
+class AdobePassIE(InfoExtractor):  # XXX: Conventionally, base classes should end with BaseIE/InfoExtractor
     _SERVICE_PROVIDER_TEMPLATE = 'https://sp.auth.adobe.com/adobe-services/%s'
     _USER_AGENT = 'Mozilla/5.0 (X11; Linux i686; rv:47.0) Gecko/20100101 Firefox/47.0'
     _MVPD_CACHE = 'ap-mvpd'
diff --git a/yt_dlp/extractor/aenetworks.py b/yt_dlp/extractor/aenetworks.py
index 516cb6302c..094c57bf92 100644
--- a/yt_dlp/extractor/aenetworks.py
+++ b/yt_dlp/extractor/aenetworks.py
@@ -8,7 +8,7 @@
 )
 
 
-class AENetworksBaseIE(ThePlatformIE):
+class AENetworksBaseIE(ThePlatformIE):  # XXX: Do not subclass from concrete IE
     _BASE_URL_REGEX = r'''(?x)https?://
         (?:(?:www|play|watch)\.)?
         (?P<domain>
@@ -304,7 +304,6 @@ def _real_extract(self, url):
 class HistoryPlayerIE(AENetworksBaseIE):
     IE_NAME = 'history:player'
     _VALID_URL = r'https?://(?:www\.)?(?P<domain>(?:history|biography)\.com)/player/(?P<id>\d+)'
-    _TESTS = []
 
     def _real_extract(self, url):
         domain, video_id = self._match_valid_url(url).groups()
diff --git a/yt_dlp/extractor/afreecatv.py b/yt_dlp/extractor/afreecatv.py
index b0fd158f61..bfcc080308 100644
--- a/yt_dlp/extractor/afreecatv.py
+++ b/yt_dlp/extractor/afreecatv.py
@@ -380,7 +380,7 @@ def _real_extract(self, url):
         return info
 
 
-class AfreecaTVLiveIE(AfreecaTVIE):
+class AfreecaTVLiveIE(AfreecaTVIE):  # XXX: Do not subclass from concrete IE
 
     IE_NAME = 'afreecatv:live'
     _VALID_URL = r'https?://play\.afreeca(?:tv)?\.com/(?P<id>[^/]+)(?:/(?P<bno>\d+))?'
diff --git a/yt_dlp/extractor/alura.py b/yt_dlp/extractor/alura.py
index b76ccb2a19..ae7115f9f1 100644
--- a/yt_dlp/extractor/alura.py
+++ b/yt_dlp/extractor/alura.py
@@ -113,7 +113,7 @@ def is_logged(webpage):
             raise ExtractorError('Unable to log in')
 
 
-class AluraCourseIE(AluraIE):
+class AluraCourseIE(AluraIE):  # XXX: Do not subclass from concrete IE
 
     _VALID_URL = r'https?://(?:cursos\.)?alura\.com\.br/course/(?P<id>[^/]+)'
     _LOGIN_URL = 'https://cursos.alura.com.br/loginForm?urlAfterLogin=/loginForm'
diff --git a/yt_dlp/extractor/amcnetworks.py b/yt_dlp/extractor/amcnetworks.py
index e04ecf65f0..9369a66f7a 100644
--- a/yt_dlp/extractor/amcnetworks.py
+++ b/yt_dlp/extractor/amcnetworks.py
@@ -9,7 +9,7 @@
 )
 
 
-class AMCNetworksIE(ThePlatformIE):
+class AMCNetworksIE(ThePlatformIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = r'https?://(?:www\.)?(?P<site>amc|bbcamerica|ifc|(?:we|sundance)tv)\.com/(?P<id>(?:movies|shows(?:/[^/]+)+)/[^/?#&]+)'
     _TESTS = [{
         'url': 'https://www.bbcamerica.com/shows/the-graham-norton-show/videos/tina-feys-adorable-airline-themed-family-dinner--51631',
diff --git a/yt_dlp/extractor/amp.py b/yt_dlp/extractor/amp.py
index 73b72b0859..6015baad55 100644
--- a/yt_dlp/extractor/amp.py
+++ b/yt_dlp/extractor/amp.py
@@ -10,7 +10,7 @@
 )
 
 
-class AMPIE(InfoExtractor):
+class AMPIE(InfoExtractor):  # XXX: Conventionally, base classes should end with BaseIE/InfoExtractor
     # parse Akamai Adaptive Media Player feed
     def _extract_feed_info(self, url):
         feed = self._download_json(
diff --git a/yt_dlp/extractor/aol.py b/yt_dlp/extractor/aol.py
index b67db2adca..5200f9d9d2 100644
--- a/yt_dlp/extractor/aol.py
+++ b/yt_dlp/extractor/aol.py
@@ -9,7 +9,7 @@
 )
 
 
-class AolIE(YahooIE):
+class AolIE(YahooIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'aol.com'
     _VALID_URL = r'(?:aol-video:|https?://(?:www\.)?aol\.(?:com|ca|co\.uk|de|jp)/video/(?:[^/]+/)*)(?P<id>\d{9}|[0-9a-f]{24}|[0-9a-f]{8}-(?:[0-9a-f]{4}-){3}[0-9a-f]{12})'
 
diff --git a/yt_dlp/extractor/audius.py b/yt_dlp/extractor/audius.py
index 0105d9db83..6448b449b9 100644
--- a/yt_dlp/extractor/audius.py
+++ b/yt_dlp/extractor/audius.py
@@ -168,7 +168,7 @@ def _real_extract(self, url):
         }
 
 
-class AudiusTrackIE(AudiusIE):
+class AudiusTrackIE(AudiusIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = r'''(?x)(?:audius:)(?:https?://(?:www\.)?.+/v1/tracks/)?(?P<track_id>\w+)'''
     IE_NAME = 'audius:track'
     IE_DESC = 'Audius track ID or API link. Prepend with "audius:"'
@@ -243,7 +243,7 @@ def _real_extract(self, url):
                                     playlist_data.get('description'))
 
 
-class AudiusProfileIE(AudiusPlaylistIE):
+class AudiusProfileIE(AudiusPlaylistIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'audius:artist'
     IE_DESC = 'Audius.co profile/artist pages'
     _VALID_URL = r'https?://(?:www)?audius\.co/(?P<id>[^\/]+)/?(?:[?#]|$)'
diff --git a/yt_dlp/extractor/aws.py b/yt_dlp/extractor/aws.py
index c2b22922be..eb831a1530 100644
--- a/yt_dlp/extractor/aws.py
+++ b/yt_dlp/extractor/aws.py
@@ -6,7 +6,7 @@
 from ..compat import compat_urllib_parse_urlencode
 
 
-class AWSIE(InfoExtractor):
+class AWSIE(InfoExtractor):  # XXX: Conventionally, base classes should end with BaseIE/InfoExtractor
     _AWS_ALGORITHM = 'AWS4-HMAC-SHA256'
     _AWS_REGION = 'us-east-1'
 
diff --git a/yt_dlp/extractor/bandaichannel.py b/yt_dlp/extractor/bandaichannel.py
index 2e32333761..e438d16ea4 100644
--- a/yt_dlp/extractor/bandaichannel.py
+++ b/yt_dlp/extractor/bandaichannel.py
@@ -2,7 +2,7 @@
 from ..utils import extract_attributes
 
 
-class BandaiChannelIE(BrightcoveNewIE):
+class BandaiChannelIE(BrightcoveNewIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'bandaichannel'
     _VALID_URL = r'https?://(?:www\.)?b-ch\.com/titles/(?P<id>\d+/\d+)'
     _TESTS = [{
diff --git a/yt_dlp/extractor/bandcamp.py b/yt_dlp/extractor/bandcamp.py
index a864ff9ac7..7dcace2c68 100644
--- a/yt_dlp/extractor/bandcamp.py
+++ b/yt_dlp/extractor/bandcamp.py
@@ -211,7 +211,7 @@ def _real_extract(self, url):
         }
 
 
-class BandcampAlbumIE(BandcampIE):
+class BandcampAlbumIE(BandcampIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'Bandcamp:album'
     _VALID_URL = r'https?://(?:(?P<subdomain>[^.]+)\.)?bandcamp\.com/album/(?P<id>[^/?#&]+)'
 
@@ -314,7 +314,7 @@ def _real_extract(self, url):
         }
 
 
-class BandcampWeeklyIE(BandcampIE):
+class BandcampWeeklyIE(BandcampIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'Bandcamp:weekly'
     _VALID_URL = r'https?://(?:www\.)?bandcamp\.com/?\?(?:.*?&)?show=(?P<id>\d+)'
     _TESTS = [{
diff --git a/yt_dlp/extractor/bbc.py b/yt_dlp/extractor/bbc.py
index fe122af853..35a7a165ca 100644
--- a/yt_dlp/extractor/bbc.py
+++ b/yt_dlp/extractor/bbc.py
@@ -588,7 +588,7 @@ def _real_extract(self, url):
         }
 
 
-class BBCIE(BBCCoUkIE):
+class BBCIE(BBCCoUkIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'bbc'
     IE_DESC = 'BBC'
     _VALID_URL = r'''(?x)
diff --git a/yt_dlp/extractor/bfmtv.py b/yt_dlp/extractor/bfmtv.py
index 48526e38b6..d86d283fac 100644
--- a/yt_dlp/extractor/bfmtv.py
+++ b/yt_dlp/extractor/bfmtv.py
@@ -42,7 +42,7 @@ def _real_extract(self, url):
         return self._brightcove_url_result(video_block['videoid'], video_block)
 
 
-class BFMTVLiveIE(BFMTVIE):
+class BFMTVLiveIE(BFMTVIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'bfmtv:live'
     _VALID_URL = BFMTVBaseIE._VALID_URL_BASE + '(?P<id>(?:[^/]+/)?en-direct)'
     _TESTS = [{
diff --git a/yt_dlp/extractor/bilibili.py b/yt_dlp/extractor/bilibili.py
index de28aa4b70..8a0e10da80 100644
--- a/yt_dlp/extractor/bilibili.py
+++ b/yt_dlp/extractor/bilibili.py
@@ -65,7 +65,7 @@ def extract_formats(self, play_info):
         missing_formats = format_names.keys() - set(traverse_obj(formats, (..., 'quality')))
         if missing_formats:
             self.to_screen(f'Format(s) {", ".join(format_names[i] for i in missing_formats)} are missing; '
-                           'you have to login or become premium member to download them')
+                           f'you have to login or become premium member to download them. {self._login_hint()}')
 
         self._sort_formats(formats)
         return formats
diff --git a/yt_dlp/extractor/cbs.py b/yt_dlp/extractor/cbs.py
index e32539c9e7..9515806eda 100644
--- a/yt_dlp/extractor/cbs.py
+++ b/yt_dlp/extractor/cbs.py
@@ -10,7 +10,7 @@
 )
 
 
-class CBSBaseIE(ThePlatformFeedIE):
+class CBSBaseIE(ThePlatformFeedIE):  # XXX: Do not subclass from concrete IE
     def _parse_smil_subtitles(self, smil, namespace=None, subtitles_lang='en'):
         subtitles = {}
         for k, ext in [('sMPTE-TTCCURL', 'tt'), ('ClosedCaptionURL', 'ttml'), ('webVTTCaptionURL', 'vtt')]:
diff --git a/yt_dlp/extractor/cbsinteractive.py b/yt_dlp/extractor/cbsinteractive.py
index 7abeecf78a..b09e9823eb 100644
--- a/yt_dlp/extractor/cbsinteractive.py
+++ b/yt_dlp/extractor/cbsinteractive.py
@@ -2,7 +2,7 @@
 from ..utils import int_or_none
 
 
-class CBSInteractiveIE(CBSIE):
+class CBSInteractiveIE(CBSIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = r'https?://(?:www\.)?(?P<site>cnet|zdnet)\.com/(?:videos|video(?:/share)?)/(?P<id>[^/?]+)'
     _TESTS = [{
         'url': 'http://www.cnet.com/videos/hands-on-with-microsofts-windows-8-1-update/',
diff --git a/yt_dlp/extractor/cbslocal.py b/yt_dlp/extractor/cbslocal.py
index c6495c95fe..3d50b0499f 100644
--- a/yt_dlp/extractor/cbslocal.py
+++ b/yt_dlp/extractor/cbslocal.py
@@ -7,7 +7,7 @@
 )
 
 
-class CBSLocalIE(AnvatoIE):
+class CBSLocalIE(AnvatoIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL_BASE = r'https?://[a-z]+\.cbslocal\.com/'
     _VALID_URL = _VALID_URL_BASE + r'video/(?P<id>\d+)'
 
@@ -47,7 +47,7 @@ def _real_extract(self, url):
             'anvato:anvato_cbslocal_app_web_prod_547f3e49241ef0e5d30c79b2efbca5d92c698f67:' + mcp_id, 'Anvato', mcp_id)
 
 
-class CBSLocalArticleIE(AnvatoIE):
+class CBSLocalArticleIE(AnvatoIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = CBSLocalIE._VALID_URL_BASE + r'\d+/\d+/\d+/(?P<id>[0-9a-z-]+)'
 
     _TESTS = [{
diff --git a/yt_dlp/extractor/cbsnews.py b/yt_dlp/extractor/cbsnews.py
index 76925b4f9b..98ec28df00 100644
--- a/yt_dlp/extractor/cbsnews.py
+++ b/yt_dlp/extractor/cbsnews.py
@@ -12,7 +12,7 @@
 )
 
 
-class CBSNewsEmbedIE(CBSIE):
+class CBSNewsEmbedIE(CBSIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'cbsnews:embed'
     _VALID_URL = r'https?://(?:www\.)?cbsnews\.com/embed/video[^#]*#(?P<id>.+)'
     _TESTS = [{
@@ -27,7 +27,7 @@ def _real_extract(self, url):
         return self._extract_video_info(item['mpxRefId'], 'cbsnews')
 
 
-class CBSNewsIE(CBSIE):
+class CBSNewsIE(CBSIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'cbsnews'
     IE_DESC = 'CBS News'
     _VALID_URL = r'https?://(?:www\.)?cbsnews\.com/(?:news|video)/(?P<id>[\da-z_-]+)'
diff --git a/yt_dlp/extractor/cmt.py b/yt_dlp/extractor/cmt.py
index 4eec066dd7..8aed7708b1 100644
--- a/yt_dlp/extractor/cmt.py
+++ b/yt_dlp/extractor/cmt.py
@@ -3,7 +3,7 @@
 # TODO Remove - Reason: Outdated Site
 
 
-class CMTIE(MTVIE):
+class CMTIE(MTVIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'cmt.com'
     _VALID_URL = r'https?://(?:www\.)?cmt\.com/(?:videos|shows|(?:full-)?episodes|video-clips)/(?P<id>[^/]+)'
 
diff --git a/yt_dlp/extractor/common.py b/yt_dlp/extractor/common.py
index 14984fd6f0..3a1af32901 100644
--- a/yt_dlp/extractor/common.py
+++ b/yt_dlp/extractor/common.py
@@ -3676,12 +3676,13 @@ def _apply_first_set_cookie_header(self, url_handle, cookie):
 
     @classmethod
     def get_testcases(cls, include_onlymatching=False):
-        t = getattr(cls, '_TEST', None)
+        # Do not look in super classes
+        t = vars(cls).get('_TEST')
         if t:
             assert not hasattr(cls, '_TESTS'), f'{cls.ie_key()}IE has _TEST and _TESTS'
             tests = [t]
         else:
-            tests = getattr(cls, '_TESTS', [])
+            tests = vars(cls).get('_TESTS', [])
         for t in tests:
             if not include_onlymatching and t.get('only_matching', False):
                 continue
@@ -3690,12 +3691,12 @@ def get_testcases(cls, include_onlymatching=False):
 
     @classmethod
     def get_webpage_testcases(cls):
-        tests = getattr(cls, '_WEBPAGE_TESTS', [])
+        tests = vars(cls).get('_WEBPAGE_TESTS', [])
         for t in tests:
             t['name'] = cls.ie_key()
         return tests
 
-    @classproperty
+    @classproperty(cache=True)
     def age_limit(cls):
         """Get age limit from the testcases"""
         return max(traverse_obj(
diff --git a/yt_dlp/extractor/corus.py b/yt_dlp/extractor/corus.py
index 7b83c0390d..8c920e3ab8 100644
--- a/yt_dlp/extractor/corus.py
+++ b/yt_dlp/extractor/corus.py
@@ -7,7 +7,7 @@
 )
 
 
-class CorusIE(ThePlatformFeedIE):
+class CorusIE(ThePlatformFeedIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = r'''(?x)
                     https?://
                         (?:www\.)?
diff --git a/yt_dlp/extractor/daum.py b/yt_dlp/extractor/daum.py
index a1f197b0bc..3ef5140658 100644
--- a/yt_dlp/extractor/daum.py
+++ b/yt_dlp/extractor/daum.py
@@ -125,7 +125,7 @@ def _real_extract(self, url):
             self._KAKAO_EMBED_BASE + video_id, 'Kakao', video_id)
 
 
-class DaumListIE(InfoExtractor):
+class DaumListIE(InfoExtractor):  # XXX: Conventionally, base classes should end with BaseIE/InfoExtractor
     def _get_entries(self, list_id, list_id_type):
         name = None
         entries = []
diff --git a/yt_dlp/extractor/dreisat.py b/yt_dlp/extractor/dreisat.py
index 80a724607c..8a59c23ab2 100644
--- a/yt_dlp/extractor/dreisat.py
+++ b/yt_dlp/extractor/dreisat.py
@@ -1,7 +1,7 @@
 from .zdf import ZDFIE
 
 
-class DreiSatIE(ZDFIE):
+class DreiSatIE(ZDFIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = '3sat'
     _VALID_URL = r'https?://(?:www\.)?3sat\.de/(?:[^/]+/)*(?P<id>[^/?#&]+)\.html'
     _TESTS = [{
diff --git a/yt_dlp/extractor/extremetube.py b/yt_dlp/extractor/extremetube.py
index 99520b6a0c..2c1969899e 100644
--- a/yt_dlp/extractor/extremetube.py
+++ b/yt_dlp/extractor/extremetube.py
@@ -2,7 +2,7 @@
 from .keezmovies import KeezMoviesIE
 
 
-class ExtremeTubeIE(KeezMoviesIE):
+class ExtremeTubeIE(KeezMoviesIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = r'https?://(?:www\.)?extremetube\.com/(?:[^/]+/)?video/(?P<id>[^/#?&]+)'
     _TESTS = [{
         'url': 'http://www.extremetube.com/video/music-video-14-british-euro-brit-european-cumshots-swallow-652431',
diff --git a/yt_dlp/extractor/fancode.py b/yt_dlp/extractor/fancode.py
index 9716e581a9..1b5db818a1 100644
--- a/yt_dlp/extractor/fancode.py
+++ b/yt_dlp/extractor/fancode.py
@@ -125,7 +125,7 @@ def _real_extract(self, url):
         }
 
 
-class FancodeLiveIE(FancodeVodIE):
+class FancodeLiveIE(FancodeVodIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'fancode:live'
 
     _VALID_URL = r'https?://(www\.)?fancode\.com/match/(?P<id>[0-9]+).+'
diff --git a/yt_dlp/extractor/hitbox.py b/yt_dlp/extractor/hitbox.py
index 6ecdd390c4..fdcf6770d5 100644
--- a/yt_dlp/extractor/hitbox.py
+++ b/yt_dlp/extractor/hitbox.py
@@ -127,7 +127,7 @@ def _real_extract(self, url):
         return metadata
 
 
-class HitboxLiveIE(HitboxIE):
+class HitboxLiveIE(HitboxIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'hitbox:live'
     _VALID_URL = r'https?://(?:www\.)?(?:hitbox|smashcast)\.tv/(?P<id>[^/?#&]+)'
     _TESTS = [{
diff --git a/yt_dlp/extractor/imgur.py b/yt_dlp/extractor/imgur.py
index a3bb476154..21c56d8791 100644
--- a/yt_dlp/extractor/imgur.py
+++ b/yt_dlp/extractor/imgur.py
@@ -138,7 +138,7 @@ def _real_extract(self, url):
         return self.url_result('http://imgur.com/%s' % gallery_id, ImgurIE.ie_key(), gallery_id)
 
 
-class ImgurAlbumIE(ImgurGalleryIE):
+class ImgurAlbumIE(ImgurGalleryIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'imgur:album'
     _VALID_URL = r'https?://(?:i\.)?imgur\.com/a/(?P<id>[a-zA-Z0-9]+)'
 
diff --git a/yt_dlp/extractor/jamendo.py b/yt_dlp/extractor/jamendo.py
index d960ee51c8..578e57a674 100644
--- a/yt_dlp/extractor/jamendo.py
+++ b/yt_dlp/extractor/jamendo.py
@@ -134,7 +134,7 @@ def _real_extract(self, url):
         }
 
 
-class JamendoAlbumIE(JamendoIE):
+class JamendoAlbumIE(JamendoIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = r'https?://(?:www\.)?jamendo\.com/album/(?P<id>[0-9]+)'
     _TESTS = [{
         'url': 'https://www.jamendo.com/album/121486/duck-on-cover',
diff --git a/yt_dlp/extractor/la7.py b/yt_dlp/extractor/la7.py
index 5d52decdba..8ce44cc134 100644
--- a/yt_dlp/extractor/la7.py
+++ b/yt_dlp/extractor/la7.py
@@ -194,7 +194,7 @@ def _real_extract(self, url):
         return self._extract_info(webpage, video_id)
 
 
-class LA7PodcastIE(LA7PodcastEpisodeIE):
+class LA7PodcastIE(LA7PodcastEpisodeIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'la7.it:podcast'
     _VALID_URL = r'(https?://)?(www\.)?la7\.it/(?P<id>[^/]+)/podcast/?(?:$|[#?])'
 
diff --git a/yt_dlp/extractor/laola1tv.py b/yt_dlp/extractor/laola1tv.py
index 4014a9256f..a90ed16a0d 100644
--- a/yt_dlp/extractor/laola1tv.py
+++ b/yt_dlp/extractor/laola1tv.py
@@ -118,7 +118,7 @@ def get_flashvar(x, *args, **kwargs):
         }
 
 
-class Laola1TvBaseIE(Laola1TvEmbedIE):
+class Laola1TvBaseIE(Laola1TvEmbedIE):  # XXX: Do not subclass from concrete IE
     def _extract_video(self, url):
         display_id = self._match_id(url)
         webpage = self._download_webpage(url, display_id)
diff --git a/yt_dlp/extractor/lcp.py b/yt_dlp/extractor/lcp.py
index 87543d56f8..9846319e0c 100644
--- a/yt_dlp/extractor/lcp.py
+++ b/yt_dlp/extractor/lcp.py
@@ -2,7 +2,7 @@
 from .arkena import ArkenaIE
 
 
-class LcpPlayIE(ArkenaIE):
+class LcpPlayIE(ArkenaIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = r'https?://play\.lcp\.fr/embed/(?P<id>[^/]+)/(?P<account_id>[^/]+)/[^/]+/[^/]+'
     _TESTS = [{
         'url': 'http://play.lcp.fr/embed/327336/131064/darkmatter/0',
diff --git a/yt_dlp/extractor/mediaset.py b/yt_dlp/extractor/mediaset.py
index ebe894f740..a3b5491d2e 100644
--- a/yt_dlp/extractor/mediaset.py
+++ b/yt_dlp/extractor/mediaset.py
@@ -286,7 +286,7 @@ def _real_extract(self, url):
         return info
 
 
-class MediasetShowIE(MediasetIE):
+class MediasetShowIE(MediasetIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = r'''(?x)
                     (?:
                         https?://
diff --git a/yt_dlp/extractor/mitele.py b/yt_dlp/extractor/mitele.py
index 12b2b2432d..ea29986729 100644
--- a/yt_dlp/extractor/mitele.py
+++ b/yt_dlp/extractor/mitele.py
@@ -5,7 +5,7 @@
 )
 
 
-class MiTeleIE(TelecincoIE):
+class MiTeleIE(TelecincoIE):  # XXX: Do not subclass from concrete IE
     IE_DESC = 'mitele.es'
     _VALID_URL = r'https?://(?:www\.)?mitele\.es/(?:[^/]+/)+(?P<id>[^/]+)/player'
 
diff --git a/yt_dlp/extractor/mofosex.py b/yt_dlp/extractor/mofosex.py
index 4221ef3e36..9cb6980c1c 100644
--- a/yt_dlp/extractor/mofosex.py
+++ b/yt_dlp/extractor/mofosex.py
@@ -7,7 +7,7 @@
 from .keezmovies import KeezMoviesIE
 
 
-class MofosexIE(KeezMoviesIE):
+class MofosexIE(KeezMoviesIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = r'https?://(?:www\.)?mofosex\.com/videos/(?P<id>\d+)/(?P<display_id>[^/?#&.]+)\.html'
     _TESTS = [{
         'url': 'http://www.mofosex.com/videos/318131/amateur-teen-playing-and-masturbating-318131.html',
diff --git a/yt_dlp/extractor/mtv.py b/yt_dlp/extractor/mtv.py
index 10cd304eb0..b2009dc5be 100644
--- a/yt_dlp/extractor/mtv.py
+++ b/yt_dlp/extractor/mtv.py
@@ -536,7 +536,7 @@ def _get_feed_query(self, uri):
         }
 
 
-class MTVItaliaProgrammaIE(MTVItaliaIE):
+class MTVItaliaProgrammaIE(MTVItaliaIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'mtv.it:programma'
     _VALID_URL = r'https?://(?:www\.)?mtv\.it/(?:programmi|playlist)/(?P<id>[0-9a-z]+)'
     _TESTS = [{
diff --git a/yt_dlp/extractor/murrtube.py b/yt_dlp/extractor/murrtube.py
index 508d512479..6cdbbda168 100644
--- a/yt_dlp/extractor/murrtube.py
+++ b/yt_dlp/extractor/murrtube.py
@@ -99,7 +99,7 @@ def _real_extract(self, url):
         }
 
 
-class MurrtubeUserIE(MurrtubeIE):
+class MurrtubeUserIE(MurrtubeIE):  # XXX: Do not subclass from concrete IE
     IE_DESC = 'Murrtube user profile'
     _VALID_URL = r'https?://murrtube\.net/(?P<id>[^/]+)$'
     _TEST = {
diff --git a/yt_dlp/extractor/musicdex.py b/yt_dlp/extractor/musicdex.py
index 4d8e74f6b4..48f29702cf 100644
--- a/yt_dlp/extractor/musicdex.py
+++ b/yt_dlp/extractor/musicdex.py
@@ -97,7 +97,7 @@ def _real_extract(self, url):
         }
 
 
-class MusicdexPageIE(MusicdexBaseIE):
+class MusicdexPageIE(MusicdexBaseIE):  # XXX: Conventionally, base classes should end with BaseIE/InfoExtractor
     def _entries(self, id):
         next_page_url = self._API_URL % id
         while next_page_url:
diff --git a/yt_dlp/extractor/nationalgeographic.py b/yt_dlp/extractor/nationalgeographic.py
index f22317d561..ad525c2589 100644
--- a/yt_dlp/extractor/nationalgeographic.py
+++ b/yt_dlp/extractor/nationalgeographic.py
@@ -59,7 +59,7 @@ def _real_extract(self, url):
         }
 
 
-class NationalGeographicTVIE(FOXIE):
+class NationalGeographicTVIE(FOXIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = r'https?://(?:www\.)?nationalgeographic\.com/tv/watch/(?P<id>[\da-fA-F]+)'
     _TESTS = [{
         'url': 'https://www.nationalgeographic.com/tv/watch/6a875e6e734b479beda26438c9f21138/',
diff --git a/yt_dlp/extractor/nbc.py b/yt_dlp/extractor/nbc.py
index 3de8c15088..dbc82de9f4 100644
--- a/yt_dlp/extractor/nbc.py
+++ b/yt_dlp/extractor/nbc.py
@@ -24,7 +24,7 @@
 )
 
 
-class NBCIE(ThePlatformIE):
+class NBCIE(ThePlatformIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = r'https?(?P<permalink>://(?:www\.)?nbc\.com/(?:classic-tv/)?[^/]+/video/[^/]+/(?P<id>n?\d+))'
 
     _TESTS = [
@@ -315,7 +315,7 @@ def _real_extract(self, url):
         }
 
 
-class NBCNewsIE(ThePlatformIE):
+class NBCNewsIE(ThePlatformIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = r'(?x)https?://(?:www\.)?(?:nbcnews|today|msnbc)\.com/([^/]+/)*(?:.*-)?(?P<id>[^/?]+)'
     _EMBED_REGEX = [r'<iframe[^>]+src=(["\'])(?P<url>(?:https?:)?//www\.nbcnews\.com/widget/video-embed/[^"\']+)\1']
 
diff --git a/yt_dlp/extractor/ndr.py b/yt_dlp/extractor/ndr.py
index ad8dbd7a77..90a658cd80 100644
--- a/yt_dlp/extractor/ndr.py
+++ b/yt_dlp/extractor/ndr.py
@@ -218,7 +218,7 @@ def _extract_embed(self, webpage, display_id, url=None):
         }
 
 
-class NDREmbedBaseIE(InfoExtractor):
+class NDREmbedBaseIE(InfoExtractor):  # XXX: Conventionally, Concrete class names do not end in BaseIE
     IE_NAME = 'ndr:embed:base'
     _VALID_URL = r'(?:ndr:(?P<id_s>[\da-z]+)|https?://www\.ndr\.de/(?P<id>[\da-z]+)-ppjson\.json)'
     _TESTS = [{
@@ -315,7 +315,7 @@ def _real_extract(self, url):
         }
 
 
-class NDREmbedIE(NDREmbedBaseIE):
+class NDREmbedIE(NDREmbedBaseIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'ndr:embed'
     _VALID_URL = r'https?://(?:\w+\.)*ndr\.de/(?:[^/]+/)*(?P<id>[\da-z]+)-(?:(?:ard)?player|externalPlayer)\.html'
     _TESTS = [{
@@ -413,7 +413,7 @@ class NDREmbedIE(NDREmbedBaseIE):
     }]
 
 
-class NJoyEmbedIE(NDREmbedBaseIE):
+class NJoyEmbedIE(NDREmbedBaseIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'njoy:embed'
     _VALID_URL = r'https?://(?:www\.)?n-joy\.de/(?:[^/]+/)*(?P<id>[\da-z]+)-(?:player|externalPlayer)_[^/]+\.html'
     _TESTS = [{
diff --git a/yt_dlp/extractor/nextmedia.py b/yt_dlp/extractor/nextmedia.py
index 1f83089fc9..0e47a4d45a 100644
--- a/yt_dlp/extractor/nextmedia.py
+++ b/yt_dlp/extractor/nextmedia.py
@@ -77,7 +77,7 @@ def _fetch_description(self, page):
         return self._og_search_property('description', page)
 
 
-class NextMediaActionNewsIE(NextMediaIE):
+class NextMediaActionNewsIE(NextMediaIE):  # XXX: Do not subclass from concrete IE
     IE_DESC = '蘋果日報 - 動新聞'
     _VALID_URL = r'https?://hk\.dv\.nextmedia\.com/actionnews/[^/]+/(?P<date>\d+)/(?P<id>\d+)/\d+'
     _TESTS = [{
@@ -102,7 +102,7 @@ def _real_extract(self, url):
         return self._extract_from_nextmedia_page(news_id, url, article_page)
 
 
-class AppleDailyIE(NextMediaIE):
+class AppleDailyIE(NextMediaIE):  # XXX: Do not subclass from concrete IE
     IE_DESC = '臺灣蘋果日報'
     _VALID_URL = r'https?://(www|ent)\.appledaily\.com\.tw/[^/]+/[^/]+/[^/]+/(?P<date>\d+)/(?P<id>\d+)(/.*)?'
     _TESTS = [{
diff --git a/yt_dlp/extractor/nick.py b/yt_dlp/extractor/nick.py
index 2a228d8de2..de22cb8d64 100644
--- a/yt_dlp/extractor/nick.py
+++ b/yt_dlp/extractor/nick.py
@@ -188,7 +188,7 @@ def _get_feed_url(self, uri, url=None):
         return self._remove_template_parameter(config['feedWithQueryParams'])
 
 
-class NickNightIE(NickDeIE):
+class NickNightIE(NickDeIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'nicknight'
     _VALID_URL = r'https?://(?:www\.)(?P<host>nicknight\.(?:de|at|tv))/(?:playlist|shows)/(?:[^/]+/)*(?P<id>[^/?#&]+)'
     _TESTS = [{
diff --git a/yt_dlp/extractor/npo.py b/yt_dlp/extractor/npo.py
index 0b5f32c2e8..b307e6a788 100644
--- a/yt_dlp/extractor/npo.py
+++ b/yt_dlp/extractor/npo.py
@@ -599,7 +599,7 @@ def _real_extract(self, url):
         }
 
 
-class NPODataMidEmbedIE(InfoExtractor):
+class NPODataMidEmbedIE(InfoExtractor):  # XXX: Conventionally, base classes should end with BaseIE/InfoExtractor
     def _real_extract(self, url):
         display_id = self._match_id(url)
         webpage = self._download_webpage(url, display_id)
@@ -653,7 +653,7 @@ class HetKlokhuisIE(NPODataMidEmbedIE):
     }
 
 
-class NPOPlaylistBaseIE(NPOIE):
+class NPOPlaylistBaseIE(NPOIE):  # XXX: Do not subclass from concrete IE
     def _real_extract(self, url):
         playlist_id = self._match_id(url)
 
diff --git a/yt_dlp/extractor/nrk.py b/yt_dlp/extractor/nrk.py
index 7eb5b21cb4..14951f8e18 100644
--- a/yt_dlp/extractor/nrk.py
+++ b/yt_dlp/extractor/nrk.py
@@ -735,7 +735,7 @@ def _real_extract(self, url):
             entries, series_id, titles.get('title'), titles.get('subtitle'))
 
 
-class NRKTVDirekteIE(NRKTVIE):
+class NRKTVDirekteIE(NRKTVIE):  # XXX: Do not subclass from concrete IE
     IE_DESC = 'NRK TV Direkte and NRK Radio Direkte'
     _VALID_URL = r'https?://(?:tv|radio)\.nrk\.no/direkte/(?P<id>[^/?#&]+)'
 
diff --git a/yt_dlp/extractor/once.py b/yt_dlp/extractor/once.py
index 460b82d02f..989f10abb1 100644
--- a/yt_dlp/extractor/once.py
+++ b/yt_dlp/extractor/once.py
@@ -3,7 +3,7 @@
 from .common import InfoExtractor
 
 
-class OnceIE(InfoExtractor):
+class OnceIE(InfoExtractor):  # XXX: Conventionally, base classes should end with BaseIE/InfoExtractor
     _VALID_URL = r'https?://.+?\.unicornmedia\.com/now/(?:ads/vmap/)?[^/]+/[^/]+/(?P<domain_id>[^/]+)/(?P<application_id>[^/]+)/(?:[^/]+/)?(?P<media_item_id>[^/]+)/content\.(?:once|m3u8|mp4)'
     ADAPTIVE_URL_TEMPLATE = 'http://once.unicornmedia.com/now/master/playlist/%s/%s/%s/content.m3u8'
     PROGRESSIVE_URL_TEMPLATE = 'http://once.unicornmedia.com/now/media/progressive/%s/%s/%s/%s/content.mp4'
diff --git a/yt_dlp/extractor/peekvids.py b/yt_dlp/extractor/peekvids.py
index f1c4469d65..fd25b5adbd 100644
--- a/yt_dlp/extractor/peekvids.py
+++ b/yt_dlp/extractor/peekvids.py
@@ -51,7 +51,7 @@ def _real_extract(self, url):
         return info
 
 
-class PlayVidsIE(PeekVidsIE):
+class PlayVidsIE(PeekVidsIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = r'https?://(?:www\.)?playvids\.com/(?:embed/|[^/]{2}/)?(?P<id>[^/?#]*)'
     _TESTS = [{
         'url': 'https://www.playvids.com/U3pBrYhsjXM/pc/dane-jones-cute-redhead-with-perfect-tits-with-mini-vamp',
diff --git a/yt_dlp/extractor/radlive.py b/yt_dlp/extractor/radlive.py
index d89c9563b2..ed38a07f03 100644
--- a/yt_dlp/extractor/radlive.py
+++ b/yt_dlp/extractor/radlive.py
@@ -94,7 +94,7 @@ def _real_extract(self, url):
         return result
 
 
-class RadLiveSeasonIE(RadLiveIE):
+class RadLiveSeasonIE(RadLiveIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'radlive:season'
     _VALID_URL = r'https?://(?:www\.)?rad\.live/content/season/(?P<id>[a-f0-9-]+)'
     _TESTS = [{
@@ -134,7 +134,7 @@ def _real_extract(self, url):
         return self.playlist_result(entries, season_id, video_info.get('title'))
 
 
-class RadLiveChannelIE(RadLiveIE):
+class RadLiveChannelIE(RadLiveIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'radlive:channel'
     _VALID_URL = r'https?://(?:www\.)?rad\.live/content/channel/(?P<id>[a-f0-9-]+)'
     _TESTS = [{
diff --git a/yt_dlp/extractor/rai.py b/yt_dlp/extractor/rai.py
index 6ed8227eb6..cd19ec07b2 100644
--- a/yt_dlp/extractor/rai.py
+++ b/yt_dlp/extractor/rai.py
@@ -356,7 +356,7 @@ def _real_extract(self, url):
         }
 
 
-class RaiPlayLiveIE(RaiPlayIE):
+class RaiPlayLiveIE(RaiPlayIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = r'(?P<base>https?://(?:www\.)?raiplay\.it/dirette/(?P<id>[^/?#&]+))'
     _TESTS = [{
         'url': 'http://www.raiplay.it/dirette/rainews24',
@@ -504,7 +504,7 @@ def _real_extract(self, url):
         }
 
 
-class RaiPlaySoundLiveIE(RaiPlaySoundIE):
+class RaiPlaySoundLiveIE(RaiPlaySoundIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = r'(?P<base>https?://(?:www\.)?raiplaysound\.it/(?P<id>[^/?#&]+)$)'
     _TESTS = [{
         'url': 'https://www.raiplaysound.it/radio2',
@@ -717,7 +717,7 @@ def _real_extract(self, url):
         }
 
 
-class RaiNewsIE(RaiIE):
+class RaiNewsIE(RaiIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = rf'https?://(www\.)?rainews\.it/(?!articoli)[^?#]+-(?P<id>{RaiBaseIE._UUID_RE})(?:-[^/?#]+)?\.html'
     _EMBED_REGEX = [rf'<iframe[^>]+data-src="(?P<url>/iframe/[^?#]+?{RaiBaseIE._UUID_RE}\.html)']
     _TESTS = [{
diff --git a/yt_dlp/extractor/redbulltv.py b/yt_dlp/extractor/redbulltv.py
index 2f0e41c5b8..50e61ba6e1 100644
--- a/yt_dlp/extractor/redbulltv.py
+++ b/yt_dlp/extractor/redbulltv.py
@@ -110,7 +110,7 @@ def _real_extract(self, url):
         return self.extract_info(video_id)
 
 
-class RedBullEmbedIE(RedBullTVIE):
+class RedBullEmbedIE(RedBullTVIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = r'https?://(?:www\.)?redbull\.com/embed/(?P<id>rrn:content:[^:]+:[\da-f]{8}-[\da-f]{4}-[\da-f]{4}-[\da-f]{4}-[\da-f]{12}:[a-z]{2}-[A-Z]{2,3})'
     _TESTS = [{
         # HLS manifest accessible only using assetId
diff --git a/yt_dlp/extractor/rts.py b/yt_dlp/extractor/rts.py
index e5ba1a26bd..6644538ed1 100644
--- a/yt_dlp/extractor/rts.py
+++ b/yt_dlp/extractor/rts.py
@@ -12,7 +12,7 @@
 )
 
 
-class RTSIE(SRGSSRIE):
+class RTSIE(SRGSSRIE):  # XXX: Do not subclass from concrete IE
     IE_DESC = 'RTS.ch'
     _VALID_URL = r'rts:(?P<rts_id>\d+)|https?://(?:.+?\.)?rts\.ch/(?:[^/]+/){2,}(?P<id>[0-9]+)-(?P<display_id>.+?)\.html'
 
diff --git a/yt_dlp/extractor/rtve.py b/yt_dlp/extractor/rtve.py
index 798dde7fa6..b9b181feb6 100644
--- a/yt_dlp/extractor/rtve.py
+++ b/yt_dlp/extractor/rtve.py
@@ -170,7 +170,7 @@ def _get_subtitles(self, video_id, sub_file):
             for s in subs)
 
 
-class RTVEAudioIE(RTVEALaCartaIE):
+class RTVEAudioIE(RTVEALaCartaIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'rtve.es:audio'
     IE_DESC = 'RTVE audio'
     _VALID_URL = r'https?://(?:www\.)?rtve\.es/(alacarta|play)/audios/[^/]+/[^/]+/(?P<id>[0-9]+)'
@@ -257,7 +257,7 @@ def _real_extract(self, url):
         }
 
 
-class RTVEInfantilIE(RTVEALaCartaIE):
+class RTVEInfantilIE(RTVEALaCartaIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'rtve.es:infantil'
     IE_DESC = 'RTVE infantil'
     _VALID_URL = r'https?://(?:www\.)?rtve\.es/infantil/serie/[^/]+/video/[^/]+/(?P<id>[0-9]+)/'
@@ -276,7 +276,7 @@ class RTVEInfantilIE(RTVEALaCartaIE):
     }]
 
 
-class RTVELiveIE(RTVEALaCartaIE):
+class RTVELiveIE(RTVEALaCartaIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'rtve.es:live'
     IE_DESC = 'RTVE.es live streams'
     _VALID_URL = r'https?://(?:www\.)?rtve\.es/directo/(?P<id>[a-zA-Z0-9-]+)'
diff --git a/yt_dlp/extractor/rutube.py b/yt_dlp/extractor/rutube.py
index 34af0d594b..cad3caa605 100644
--- a/yt_dlp/extractor/rutube.py
+++ b/yt_dlp/extractor/rutube.py
@@ -240,7 +240,6 @@ class RutubeMovieIE(RutubePlaylistBaseIE):
     IE_NAME = 'rutube:movie'
     IE_DESC = 'Rutube movies'
     _VALID_URL = r'https?://rutube\.ru/metainfo/tv/(?P<id>\d+)'
-    _TESTS = []
 
     _MOVIE_TEMPLATE = 'http://rutube.ru/api/metainfo/tv/%s/?format=json'
     _PAGE_TEMPLATE = 'http://rutube.ru/api/metainfo/tv/%s/video?page=%s&format=json'
diff --git a/yt_dlp/extractor/sevenplus.py b/yt_dlp/extractor/sevenplus.py
index 8e95bc230d..36d1a86fdd 100644
--- a/yt_dlp/extractor/sevenplus.py
+++ b/yt_dlp/extractor/sevenplus.py
@@ -13,7 +13,7 @@
 )
 
 
-class SevenPlusIE(BrightcoveNewIE):
+class SevenPlusIE(BrightcoveNewIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = '7plus'
     _VALID_URL = r'https?://(?:www\.)?7plus\.com\.au/(?P<path>[^?]+\?.*?\bepisode-id=(?P<id>[^&#]+))'
     _TESTS = [{
diff --git a/yt_dlp/extractor/skyit.py b/yt_dlp/extractor/skyit.py
index 2daaaf75c1..9e4d7d35de 100644
--- a/yt_dlp/extractor/skyit.py
+++ b/yt_dlp/extractor/skyit.py
@@ -70,7 +70,7 @@ def _real_extract(self, url):
         return self._parse_video(video, video_id)
 
 
-class SkyItVideoIE(SkyItPlayerIE):
+class SkyItVideoIE(SkyItPlayerIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'video.sky.it'
     _VALID_URL = r'https?://(?:masterchef|video|xfactor)\.sky\.it(?:/[^/]+)*/video/[0-9a-z-]+-(?P<id>\d+)'
     _TESTS = [{
@@ -99,7 +99,7 @@ def _real_extract(self, url):
         return self._player_url_result(video_id)
 
 
-class SkyItVideoLiveIE(SkyItPlayerIE):
+class SkyItVideoLiveIE(SkyItPlayerIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'video.sky.it:live'
     _VALID_URL = r'https?://video\.sky\.it/diretta/(?P<id>[^/?&#]+)'
     _TEST = {
@@ -127,7 +127,7 @@ def _real_extract(self, url):
         return self._parse_video(livestream, asset_id)
 
 
-class SkyItIE(SkyItPlayerIE):
+class SkyItIE(SkyItPlayerIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'sky.it'
     _VALID_URL = r'https?://(?:sport|tg24)\.sky\.it(?:/[^/]+)*/\d{4}/\d{2}/\d{2}/(?P<id>[^/?&#]+)'
     _TESTS = [{
@@ -166,7 +166,7 @@ def _real_extract(self, url):
         return self._player_url_result(video_id)
 
 
-class SkyItArteIE(SkyItIE):
+class SkyItArteIE(SkyItIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'arte.sky.it'
     _VALID_URL = r'https?://arte\.sky\.it/video/(?P<id>[^/?&#]+)'
     _TESTS = [{
@@ -187,7 +187,7 @@ class SkyItArteIE(SkyItIE):
     _VIDEO_ID_REGEX = r'"embedUrl"\s*:\s*"(?:https:)?//player\.sky\.it/player/external\.html\?[^"]*\bid=(\d+)'
 
 
-class CieloTVItIE(SkyItIE):
+class CieloTVItIE(SkyItIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'cielotv.it'
     _VALID_URL = r'https?://(?:www\.)?cielotv\.it/video/(?P<id>[^.]+)\.html'
     _TESTS = [{
@@ -208,7 +208,7 @@ class CieloTVItIE(SkyItIE):
     _VIDEO_ID_REGEX = r'videoId\s*=\s*"(\d+)"'
 
 
-class TV8ItIE(SkyItVideoIE):
+class TV8ItIE(SkyItVideoIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'tv8.it'
     _VALID_URL = r'https?://(?:www\.)?tv8\.it/(?:show)?video/[0-9a-z-]+-(?P<id>\d+)'
     _TESTS = [{
diff --git a/yt_dlp/extractor/southpark.py b/yt_dlp/extractor/southpark.py
index 7381ac3624..e23f192a1c 100644
--- a/yt_dlp/extractor/southpark.py
+++ b/yt_dlp/extractor/southpark.py
@@ -34,7 +34,7 @@ def _get_feed_query(self, uri):
         }
 
 
-class SouthParkEsIE(SouthParkIE):
+class SouthParkEsIE(SouthParkIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'southpark.cc.com:español'
     _VALID_URL = r'https?://(?:www\.)?(?P<url>southpark\.cc\.com/es/episodios/(?P<id>.+?)(\?|#|$))'
     _LANG = 'es'
@@ -50,7 +50,7 @@ class SouthParkEsIE(SouthParkIE):
     }]
 
 
-class SouthParkDeIE(SouthParkIE):
+class SouthParkDeIE(SouthParkIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'southpark.de'
     _VALID_URL = r'https?://(?:www\.)?(?P<url>southpark\.de/(?:(en/(videoclip|collections|episodes|video-clips))|(videoclip|collections|folgen))/(?P<id>(?P<unique_id>.+?)/.+?)(?:\?|#|$))'
     _TESTS = [{
@@ -109,7 +109,7 @@ def _get_feed_query(self, uri):
         return
 
 
-class SouthParkLatIE(SouthParkIE):
+class SouthParkLatIE(SouthParkIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'southpark.lat'
     _VALID_URL = r'https?://(?:www\.)?southpark\.lat/(?:en/)?(?:video-?clips?|collections|episod(?:e|io)s)/(?P<id>[^/?#&]+)'
     _TESTS = [{
@@ -152,7 +152,7 @@ def _get_feed_query(self, uri):
         return
 
 
-class SouthParkNlIE(SouthParkIE):
+class SouthParkNlIE(SouthParkIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'southpark.nl'
     _VALID_URL = r'https?://(?:www\.)?(?P<url>southpark\.nl/(?:clips|(?:full-)?episodes|collections)/(?P<id>.+?)(\?|#|$))'
     _FEED_URL = 'http://www.southpark.nl/feeds/video-player/mrss/'
@@ -167,7 +167,7 @@ class SouthParkNlIE(SouthParkIE):
     }]
 
 
-class SouthParkDkIE(SouthParkIE):
+class SouthParkDkIE(SouthParkIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'southparkstudios.dk'
     _VALID_URL = r'https?://(?:www\.)?(?P<url>southparkstudios\.(?:dk|nu)/(?:clips|full-episodes|collections)/(?P<id>.+?)(\?|#|$))'
     _FEED_URL = 'http://www.southparkstudios.dk/feeds/video-player/mrss/'
diff --git a/yt_dlp/extractor/tele5.py b/yt_dlp/extractor/tele5.py
index 58d343b449..9260db2b44 100644
--- a/yt_dlp/extractor/tele5.py
+++ b/yt_dlp/extractor/tele5.py
@@ -6,7 +6,7 @@
 )
 
 
-class Tele5IE(DPlayIE):
+class Tele5IE(DPlayIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = r'https?://(?:www\.)?tele5\.de/(?:[^/]+/)*(?P<id>[^/?#&]+)'
     _GEO_COUNTRIES = ['DE']
     _TESTS = [{
diff --git a/yt_dlp/extractor/theweatherchannel.py b/yt_dlp/extractor/theweatherchannel.py
index 9e94cd1ea1..4f6d2ecbad 100644
--- a/yt_dlp/extractor/theweatherchannel.py
+++ b/yt_dlp/extractor/theweatherchannel.py
@@ -8,7 +8,7 @@
 )
 
 
-class TheWeatherChannelIE(ThePlatformIE):
+class TheWeatherChannelIE(ThePlatformIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = r'https?://(?:www\.)?weather\.com(?P<asset_name>(?:/(?P<locale>[a-z]{2}-[A-Z]{2}))?/(?:[^/]+/)*video/(?P<id>[^/?#]+))'
     _TESTS = [{
         'url': 'https://weather.com/series/great-outdoors/video/ice-climber-is-in-for-a-shock',
diff --git a/yt_dlp/extractor/tiktok.py b/yt_dlp/extractor/tiktok.py
index 4a35a241c7..79a2238612 100644
--- a/yt_dlp/extractor/tiktok.py
+++ b/yt_dlp/extractor/tiktok.py
@@ -655,7 +655,7 @@ def _real_extract(self, url):
         return self.playlist_result(self._entries_api(user_id, videos), user_id, user_name, thumbnail=thumbnail)
 
 
-class TikTokBaseListIE(TikTokBaseIE):
+class TikTokBaseListIE(TikTokBaseIE):  # XXX: Conventionally, base classes should end with BaseIE/InfoExtractor
     def _entries(self, list_id, display_id):
         query = {
             self._QUERY_NAME: list_id,
@@ -764,7 +764,7 @@ def _real_extract(self, url):
         return self.playlist_result(self._entries(tag_id, display_id), tag_id, display_id)
 
 
-class DouyinIE(TikTokIE):
+class DouyinIE(TikTokIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = r'https?://(?:www\.)?douyin\.com/video/(?P<id>[0-9]+)'
     _TESTS = [{
         'url': 'https://www.douyin.com/video/6961737553342991651',
diff --git a/yt_dlp/extractor/toutv.py b/yt_dlp/extractor/toutv.py
index 349c0bded9..f60c199f0e 100644
--- a/yt_dlp/extractor/toutv.py
+++ b/yt_dlp/extractor/toutv.py
@@ -9,7 +9,7 @@
 )
 
 
-class TouTvIE(RadioCanadaIE):
+class TouTvIE(RadioCanadaIE):  # XXX: Do not subclass from concrete IE
     _NETRC_MACHINE = 'toutv'
     IE_NAME = 'tou.tv'
     _VALID_URL = r'https?://ici\.tou\.tv/(?P<id>[a-zA-Z0-9_-]+(?:/S[0-9]+[EC][0-9]+)?)'
diff --git a/yt_dlp/extractor/tube8.py b/yt_dlp/extractor/tube8.py
index b092ecad5a..77ed05ffda 100644
--- a/yt_dlp/extractor/tube8.py
+++ b/yt_dlp/extractor/tube8.py
@@ -7,7 +7,7 @@
 from .keezmovies import KeezMoviesIE
 
 
-class Tube8IE(KeezMoviesIE):
+class Tube8IE(KeezMoviesIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = r'https?://(?:www\.)?tube8\.com/(?:[^/]+/)+(?P<display_id>[^/]+)/(?P<id>\d+)'
     _EMBED_REGEX = [r'<iframe[^>]+\bsrc=["\'](?P<url>(?:https?:)?//(?:www\.)?tube8\.com/embed/(?:[^/]+/)+\d+)']
     _TESTS = [{
diff --git a/yt_dlp/extractor/tvnow.py b/yt_dlp/extractor/tvnow.py
index 4aa558d839..24add52605 100644
--- a/yt_dlp/extractor/tvnow.py
+++ b/yt_dlp/extractor/tvnow.py
@@ -426,7 +426,7 @@ def _real_extract(self, url):
         return self._extract_video(info, video_id, display_id)
 
 
-class TVNowFilmIE(TVNowIE):
+class TVNowFilmIE(TVNowIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = r'''(?x)
                     (?P<base_url>https?://
                         (?:www\.)?tvnow\.(?:de|at|ch)/
diff --git a/yt_dlp/extractor/udemy.py b/yt_dlp/extractor/udemy.py
index 1dc2dbdc46..2c8a35473c 100644
--- a/yt_dlp/extractor/udemy.py
+++ b/yt_dlp/extractor/udemy.py
@@ -405,7 +405,7 @@ def extract_subtitles(track_list):
         }
 
 
-class UdemyCourseIE(UdemyIE):
+class UdemyCourseIE(UdemyIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'udemy:course'
     _VALID_URL = r'https?://(?:[^/]+\.)?udemy\.com/(?P<id>[^/?#&]+)'
     _TESTS = [{
diff --git a/yt_dlp/extractor/uplynk.py b/yt_dlp/extractor/uplynk.py
index 04c96f388c..9b560f7196 100644
--- a/yt_dlp/extractor/uplynk.py
+++ b/yt_dlp/extractor/uplynk.py
@@ -52,10 +52,9 @@ def _real_extract(self, url):
         return self._extract_uplynk_info(url)
 
 
-class UplynkPreplayIE(UplynkIE):
+class UplynkPreplayIE(UplynkIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'uplynk:preplay'
     _VALID_URL = r'https?://.*?\.uplynk\.com/preplay2?/(?P<path>ext/[0-9a-f]{32}/(?P<external_id>[^/?&]+)|(?P<id>[0-9a-f]{32}))\.json'
-    _TEST = None
 
     def _real_extract(self, url):
         path, external_id, video_id = self._match_valid_url(url).groups()
diff --git a/yt_dlp/extractor/usanetwork.py b/yt_dlp/extractor/usanetwork.py
index d6b58a51c4..4a06a9ad40 100644
--- a/yt_dlp/extractor/usanetwork.py
+++ b/yt_dlp/extractor/usanetwork.py
@@ -1,7 +1,7 @@
 from .nbc import NBCIE
 
 
-class USANetworkIE(NBCIE):
+class USANetworkIE(NBCIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = r'https?(?P<permalink>://(?:www\.)?usanetwork\.com/(?:[^/]+/videos?|movies?)/(?:[^/]+/)?(?P<id>\d+))'
     _TESTS = [{
         'url': 'https://www.usanetwork.com/peacock-trailers/video/intelligence-trailer/4185302',
diff --git a/yt_dlp/extractor/veoh.py b/yt_dlp/extractor/veoh.py
index a32c2fccb9..d9b3ab115a 100644
--- a/yt_dlp/extractor/veoh.py
+++ b/yt_dlp/extractor/veoh.py
@@ -130,7 +130,7 @@ def _real_extract(self, url):
         }
 
 
-class VeohUserIE(VeohIE):
+class VeohUserIE(VeohIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = r'https?://(?:www\.)?veoh\.com/users/(?P<id>[\w-]+)'
     IE_NAME = 'veoh:user'
 
diff --git a/yt_dlp/extractor/vgtv.py b/yt_dlp/extractor/vgtv.py
index 3e0af7fb23..b637afddf1 100644
--- a/yt_dlp/extractor/vgtv.py
+++ b/yt_dlp/extractor/vgtv.py
@@ -9,7 +9,7 @@
 )
 
 
-class VGTVIE(XstreamIE):
+class VGTVIE(XstreamIE):  # XXX: Do not subclass from concrete IE
     IE_DESC = 'VGTV, BTTV, FTV, Aftenposten and Aftonbladet'
     _GEO_BYPASS = False
 
diff --git a/yt_dlp/extractor/vimeo.py b/yt_dlp/extractor/vimeo.py
index 2e36b8861a..1b21c00501 100644
--- a/yt_dlp/extractor/vimeo.py
+++ b/yt_dlp/extractor/vimeo.py
@@ -1004,7 +1004,7 @@ def is_rented():
         return merge_dicts(info_dict, info_dict_config, json_ld)
 
 
-class VimeoOndemandIE(VimeoIE):
+class VimeoOndemandIE(VimeoIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'vimeo:ondemand'
     _VALID_URL = r'https?://(?:www\.)?vimeo\.com/ondemand/(?:[^/]+/)?(?P<id>[^/?#&]+)'
     _TESTS = [{
@@ -1129,7 +1129,7 @@ def _real_extract(self, url):
         return self._extract_videos(channel_id, self._BASE_URL_TEMPL % channel_id)
 
 
-class VimeoUserIE(VimeoChannelIE):
+class VimeoUserIE(VimeoChannelIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'vimeo:user'
     _VALID_URL = r'https://vimeo\.com/(?!(?:[0-9]+|watchlater)(?:$|[?#/]))(?P<id>[^/]+)(?:/videos)?/?(?:$|[?#])'
     _TITLE_RE = r'<a[^>]+?class="user">([^<>]+?)</a>'
@@ -1239,7 +1239,7 @@ def _real_extract(self, url):
             entries, album_id, album.get('name'), album.get('description'))
 
 
-class VimeoGroupsIE(VimeoChannelIE):
+class VimeoGroupsIE(VimeoChannelIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'vimeo:group'
     _VALID_URL = r'https://vimeo\.com/groups/(?P<id>[^/]+)(?:/(?!videos?/\d+)|$)'
     _TESTS = [{
@@ -1331,7 +1331,7 @@ def _real_extract(self, url):
         return info_dict
 
 
-class VimeoWatchLaterIE(VimeoChannelIE):
+class VimeoWatchLaterIE(VimeoChannelIE):  # XXX: Do not subclass from concrete IE
     IE_NAME = 'vimeo:watchlater'
     IE_DESC = 'Vimeo watch later list, ":vimeowatchlater" keyword (requires authentication)'
     _VALID_URL = r'https://vimeo\.com/(?:home/)?watchlater|:vimeowatchlater'
@@ -1354,7 +1354,7 @@ def _real_extract(self, url):
         return self._extract_videos('watchlater', 'https://vimeo.com/watchlater')
 
 
-class VimeoLikesIE(VimeoChannelIE):
+class VimeoLikesIE(VimeoChannelIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = r'https://(?:www\.)?vimeo\.com/(?P<id>[^/]+)/likes/?(?:$|[?#]|sort:)'
     IE_NAME = 'vimeo:likes'
     IE_DESC = 'Vimeo user likes'
diff --git a/yt_dlp/extractor/vvvvid.py b/yt_dlp/extractor/vvvvid.py
index f0156d10ca..0c3e83a0a8 100644
--- a/yt_dlp/extractor/vvvvid.py
+++ b/yt_dlp/extractor/vvvvid.py
@@ -242,7 +242,7 @@ def metadata_from_url(r_url):
         return info
 
 
-class VVVVIDShowIE(VVVVIDIE):
+class VVVVIDShowIE(VVVVIDIE):  # XXX: Do not subclass from concrete IE
     _VALID_URL = r'(?P<base_url>%s(?P<id>\d+)(?:/(?P<show_title>[^/?&#]+))?)/?(?:[?#&]|$)' % VVVVIDIE._VALID_URL_BASE
     _TESTS = [{
         'url': 'https://www.vvvvid.it/show/156/psyco-pass',
diff --git a/yt_dlp/extractor/wdr.py b/yt_dlp/extractor/wdr.py
index d0ad69477d..7b2e7c8e06 100644
--- a/yt_dlp/extractor/wdr.py
+++ b/yt_dlp/extractor/wdr.py
@@ -133,7 +133,7 @@ def _real_extract(self, url):
         }
 
 
-class WDRPageIE(WDRIE):
+class WDRPageIE(WDRIE):  # XXX: Do not subclass from concrete IE
     _MAUS_REGEX = r'https?://(?:www\.)wdrmaus.de/(?:[^/]+/)*?(?P<maus_id>[^/?#.]+)(?:/?|/index\.php5|\.php5)$'
     _PAGE_REGEX = r'/(?:mediathek/)?(?:[^/]+/)*(?P<display_id>[^/]+)\.html'
     _VALID_URL = r'https?://(?:www\d?\.)?(?:(?:kinder\.)?wdr\d?|sportschau)\.de' + _PAGE_REGEX + '|' + _MAUS_REGEX
diff --git a/yt_dlp/extractor/youtube.py b/yt_dlp/extractor/youtube.py
index 9d51f38ba1..7e3530c0fa 100644
--- a/yt_dlp/extractor/youtube.py
+++ b/yt_dlp/extractor/youtube.py
@@ -1051,7 +1051,7 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
             <a\s[^>]*\bhref="(?P<url>https://www\.youtube\.com/watch\?v=[0-9A-Za-z_-]{11})"
             \s[^>]*\bclass="[^"]*\blazy-load-youtube''',
     ]
-    _RETURN_TYPE = 'video'  # While there are "multifeed" test cases, they don't seem to actually exist anymore
+    _RETURN_TYPE = 'video'  # XXX: How to handle multifeed?
 
     _PLAYER_INFO_RE = (
         r'/s/player/(?P<id>[a-zA-Z0-9_-]{8,})/player',
@@ -1582,66 +1582,99 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
             'skip': 'This live event has ended.',
         },
         {
-            # Multifeed videos (multiple cameras), URL is for Main Camera
-            'url': 'https://www.youtube.com/watch?v=jvGDaLqkpTg',
+            # Multifeed videos (multiple cameras), URL can be of any Camera
+            'url': 'https://www.youtube.com/watch?v=zaPI8MvL8pg',
             'info_dict': {
-                'id': 'jvGDaLqkpTg',
-                'title': 'Tom Clancy Free Weekend Rainbow Whatever',
-                'description': 'md5:e03b909557865076822aa169218d6a5d',
+                'id': 'zaPI8MvL8pg',
+                'title': 'Terraria 1.2 Live Stream | Let\'s Play - Part 04',
+                'description': 'md5:563ccbc698b39298481ca3c571169519',
             },
             'playlist': [{
                 'info_dict': {
-                    'id': 'jvGDaLqkpTg',
+                    'id': 'j5yGuxZ8lLU',
                     'ext': 'mp4',
-                    'title': 'Tom Clancy Free Weekend Rainbow Whatever (Main Camera)',
-                    'description': 'md5:e03b909557865076822aa169218d6a5d',
-                    'duration': 10643,
-                    'upload_date': '20161111',
-                    'uploader': 'Team PGP',
-                    'uploader_id': 'UChORY56LMMETTuGjXaJXvLg',
-                    'uploader_url': r're:https?://(?:www\.)?youtube\.com/channel/UChORY56LMMETTuGjXaJXvLg',
+                    'title': 'Terraria 1.2 Live Stream | Let\'s Play - Part 04 (Chris)',
+                    'uploader': 'WiiLikeToPlay',
+                    'description': 'md5:563ccbc698b39298481ca3c571169519',
+                    'uploader_url': 'http://www.youtube.com/user/WiiRikeToPray',
+                    'duration': 10120,
+                    'channel_follower_count': int,
+                    'channel_url': 'https://www.youtube.com/channel/UCN2XePorRokPB9TEgRZpddg',
+                    'availability': 'public',
+                    'playable_in_embed': True,
+                    'upload_date': '20131105',
+                    'uploader_id': 'WiiRikeToPray',
+                    'categories': ['Gaming'],
+                    'live_status': 'was_live',
+                    'tags': 'count:24',
+                    'release_timestamp': 1383701910,
+                    'thumbnail': 'https://i.ytimg.com/vi/j5yGuxZ8lLU/maxresdefault.jpg',
+                    'comment_count': int,
+                    'age_limit': 0,
+                    'like_count': int,
+                    'channel_id': 'UCN2XePorRokPB9TEgRZpddg',
+                    'channel': 'WiiLikeToPlay',
+                    'view_count': int,
+                    'release_date': '20131106',
                 },
             }, {
                 'info_dict': {
-                    'id': '3AKt1R1aDnw',
+                    'id': 'zaPI8MvL8pg',
                     'ext': 'mp4',
-                    'title': 'Tom Clancy Free Weekend Rainbow Whatever (Camera 2)',
-                    'description': 'md5:e03b909557865076822aa169218d6a5d',
-                    'duration': 10991,
-                    'upload_date': '20161111',
-                    'uploader': 'Team PGP',
-                    'uploader_id': 'UChORY56LMMETTuGjXaJXvLg',
-                    'uploader_url': r're:https?://(?:www\.)?youtube\.com/channel/UChORY56LMMETTuGjXaJXvLg',
+                    'title': 'Terraria 1.2 Live Stream | Let\'s Play - Part 04 (Tyson)',
+                    'uploader_id': 'WiiRikeToPray',
+                    'availability': 'public',
+                    'channel_url': 'https://www.youtube.com/channel/UCN2XePorRokPB9TEgRZpddg',
+                    'channel': 'WiiLikeToPlay',
+                    'uploader_url': 'http://www.youtube.com/user/WiiRikeToPray',
+                    'channel_follower_count': int,
+                    'description': 'md5:563ccbc698b39298481ca3c571169519',
+                    'duration': 10108,
+                    'age_limit': 0,
+                    'like_count': int,
+                    'tags': 'count:24',
+                    'channel_id': 'UCN2XePorRokPB9TEgRZpddg',
+                    'uploader': 'WiiLikeToPlay',
+                    'release_timestamp': 1383701915,
+                    'comment_count': int,
+                    'upload_date': '20131105',
+                    'thumbnail': 'https://i.ytimg.com/vi/zaPI8MvL8pg/maxresdefault.jpg',
+                    'release_date': '20131106',
+                    'playable_in_embed': True,
+                    'live_status': 'was_live',
+                    'categories': ['Gaming'],
+                    'view_count': int,
                 },
             }, {
                 'info_dict': {
-                    'id': 'RtAMM00gpVc',
+                    'id': 'R7r3vfO7Hao',
                     'ext': 'mp4',
-                    'title': 'Tom Clancy Free Weekend Rainbow Whatever (Camera 3)',
-                    'description': 'md5:e03b909557865076822aa169218d6a5d',
-                    'duration': 10995,
-                    'upload_date': '20161111',
-                    'uploader': 'Team PGP',
-                    'uploader_id': 'UChORY56LMMETTuGjXaJXvLg',
-                    'uploader_url': r're:https?://(?:www\.)?youtube\.com/channel/UChORY56LMMETTuGjXaJXvLg',
-                },
-            }, {
-                'info_dict': {
-                    'id': '6N2fdlP3C5U',
-                    'ext': 'mp4',
-                    'title': 'Tom Clancy Free Weekend Rainbow Whatever (Camera 4)',
-                    'description': 'md5:e03b909557865076822aa169218d6a5d',
-                    'duration': 10990,
-                    'upload_date': '20161111',
-                    'uploader': 'Team PGP',
-                    'uploader_id': 'UChORY56LMMETTuGjXaJXvLg',
-                    'uploader_url': r're:https?://(?:www\.)?youtube\.com/channel/UChORY56LMMETTuGjXaJXvLg',
+                    'title': 'Terraria 1.2 Live Stream | Let\'s Play - Part 04 (Spencer)',
+                    'thumbnail': 'https://i.ytimg.com/vi/R7r3vfO7Hao/maxresdefault.jpg',
+                    'channel_id': 'UCN2XePorRokPB9TEgRZpddg',
+                    'like_count': int,
+                    'availability': 'public',
+                    'playable_in_embed': True,
+                    'upload_date': '20131105',
+                    'description': 'md5:563ccbc698b39298481ca3c571169519',
+                    'uploader_id': 'WiiRikeToPray',
+                    'uploader_url': 'http://www.youtube.com/user/WiiRikeToPray',
+                    'channel_follower_count': int,
+                    'tags': 'count:24',
+                    'release_date': '20131106',
+                    'uploader': 'WiiLikeToPlay',
+                    'comment_count': int,
+                    'channel_url': 'https://www.youtube.com/channel/UCN2XePorRokPB9TEgRZpddg',
+                    'channel': 'WiiLikeToPlay',
+                    'categories': ['Gaming'],
+                    'release_timestamp': 1383701914,
+                    'live_status': 'was_live',
+                    'age_limit': 0,
+                    'duration': 10128,
+                    'view_count': int,
                 },
             }],
-            'params': {
-                'skip_download': True,
-            },
-            'skip': 'Not multifeed anymore',
+            'params': {'skip_download': True},
         },
         {
             # Multifeed video with comma in title (see https://github.com/ytdl-org/youtube-dl/issues/8536)
diff --git a/yt_dlp/utils.py b/yt_dlp/utils.py
index a6bf897dcd..7cba13678f 100644
--- a/yt_dlp/utils.py
+++ b/yt_dlp/utils.py
@@ -5839,7 +5839,7 @@ def wrapper(self, *args, **kwargs):
         bound_args.apply_defaults()
         key = tuple(bound_args.arguments.values())[1:]
 
-        cache = vars(self).setdefault('__cached_method__cache', {}).setdefault(f.__name__, {})
+        cache = vars(self).setdefault('_cached_method__cache', {}).setdefault(f.__name__, {})
         if key not in cache:
             cache[key] = f(self, *args, **kwargs)
         return cache[key]