[ard:mediathek] Fix video id extraction (Closes #202)

yt_dlp/extractor/ard.py

@@ -272,7 +272,8 @@ class ARDMediathekIE(ARDMediathekBaseIE):
         else:  # request JSON file
             if not document_id:
                 video_id = self._search_regex(
-                    r'/play/(?:config|media)/(\d+)', webpage, 'media id')
+                    (r'/play/(?:config|media|sola)/(\d+)', r'contentId["\']\s*:\s*(\d+)'),
+                    webpage, 'media id', default=None)
             info = self._extract_media_info(
                 'http://www.ardmediathek.de/play/media/%s' % video_id,
                 webpage, video_id)