[youtube:playlist] Relax _VIDEO_RE (closes #21844)

youtube_dl/extractor/youtube.py

@@ -2432,7 +2432,7 @@ class YoutubePlaylistIE(YoutubePlaylistBaseInfoExtractor):
                         (%(playlist_id)s)
                      )""" % {'playlist_id': YoutubeBaseInfoExtractor._PLAYLIST_ID_RE}
     _TEMPLATE_URL = 'https://www.youtube.com/playlist?list=%s'
-    _VIDEO_RE = r'href="\s*/watch\?v=(?P<id>[0-9A-Za-z_-]{11})&amp;[^"]*?index=(?P<index>\d+)(?:[^>]+>(?P<title>[^<]+))?'
+    _VIDEO_RE = r'href="\s*/watch\?v=(?P<id>[0-9A-Za-z_-]{11})(?:&amp;(?:[^"]*?index=(?P<index>\d+))?(?:[^>]+>(?P<title>[^<]+))?)?'
     IE_NAME = 'youtube:playlist'
     _TESTS = [{
         'url': 'https://www.youtube.com/playlist?list=PLwiyx1dc3P2JR9N8gQaQN_BCvlSlap7re',
@@ -2556,6 +2556,16 @@ class YoutubePlaylistIE(YoutubePlaylistBaseInfoExtractor):
             'noplaylist': True,
             'skip_download': True,
         },
+    }, {
+        # https://github.com/ytdl-org/youtube-dl/issues/21844
+        'url': 'https://www.youtube.com/playlist?list=PLzH6n4zXuckpfMu_4Ff8E7Z1behQks5ba',
+        'info_dict': {
+            'title': 'Data Analysis with Dr Mike Pound',
+            'id': 'PLzH6n4zXuckpfMu_4Ff8E7Z1behQks5ba',
+            'uploader_id': 'Computerphile',
+            'uploader': 'Computerphile',
+        },
+        'playlist_mincount': 11,
     }, {
         'url': 'https://youtu.be/uWyaPkt-VOI?list=PL9D9FC436B881BA21',
         'only_matching': True,