[youtube] get mix playlist title from ytInitialData

youtube_dlc/extractor/youtube.py

@@ -2825,6 +2825,7 @@ class YoutubePlaylistIE(YoutubePlaylistBaseInfoExtractor):
         # The mixes are generated from a single video
         # the id of the playlist is just 'RD' + video_id
         ids = []
+        yt_initial = None
         last_id = playlist_id[-11:]
         for n in itertools.count(1):
             url = 'https://www.youtube.com/watch?v=%s&list=%s' % (last_id, playlist_id)
@@ -2858,6 +2859,9 @@ class YoutubePlaylistIE(YoutubePlaylistBaseInfoExtractor):
             or search_title('title'))
         title = clean_html(title_span)
 
+        if not title:
+            title = try_get(yt_initial, lambda x: x['contents']['twoColumnWatchNextResults']['playlist']['playlist']['title'], compat_str)
+
         return self.playlist_result(url_results, playlist_id, title)
 
     def _extract_playlist(self, playlist_id):