diff --git a/yt_dlp/extractor/common.py b/yt_dlp/extractor/common.py
index af534775f..918141c3b 100644
--- a/yt_dlp/extractor/common.py
+++ b/yt_dlp/extractor/common.py
@@ -2334,7 +2334,7 @@ def _parse_smil_formats_and_subtitles(
         for meta in smil.findall(self._xpath_ns('./head/meta', namespace)):
             b = meta.get('base') or meta.get('httpBase')
             if b:
-                base = b
+                base = f'{b}/'
                 break
 
         formats, subtitles = [], {}