Improve URL extraction

youtube_dl/extractor/turner.py

@@ -15,6 +15,7 @@ from ..utils import (
     update_url_query,
     ExtractorError,
     strip_or_none,
+    url_or_none,
 )
 
 
@@ -154,8 +155,8 @@ class TurnerBaseIE(AdobePassIE):
         subtitles = {}
         for source in video_data.findall('closedCaptions/source'):
             for track in source.findall('track'):
-                track_url = track.get('url')
-                if not isinstance(track_url, compat_str) or track_url.endswith('/big'):
+                track_url = url_or_none(track.get('url'))
+                if not track_url or track_url.endswith('/big'):
                     continue
                 lang = track.get('lang') or track.get('label') or 'en'
                 subtitles.setdefault(lang, []).append({