+        subtitles = {}
+        captions = source.get('captionsAvailableLanguages')
+        if isinstance(captions, dict):
+            for lang, subtitle_url in captions.items():
+                subtitle_url = url_or_none(subtitle_url)
+                if lang != 'none' and subtitle_url:
+                    subtitles.setdefault(lang, []).append({'url': subtitle_url})
+