diff --git a/youtube_dl/extractor/sockshare.py b/youtube_dl/extractor/sockshare.py
index 75b634bc6..dc9f80550 100644
--- a/youtube_dl/extractor/sockshare.py
+++ b/youtube_dl/extractor/sockshare.py
@@ -5,6 +5,7 @@
     ExtractorError,
     compat_urllib_parse,
     compat_urllib_request,
+    determine_ext,
 )
 import re
 
@@ -68,6 +69,7 @@ def _real_extract(self, url):
         formats = [{
             'format_id': 'sd',
             'url': video_url,
+            'ext': determine_ext(title),
         }]
 
         return {