[outtmpl] Make `%s` work in strfformat for all systems

yt_dlp/utils.py

@@ -2567,6 +2567,8 @@ def strftime_or_none(timestamp, date_format, default=None):
             datetime_object = datetime.datetime.utcfromtimestamp(timestamp)
         elif isinstance(timestamp, str):  # assume YYYYMMDD
             datetime_object = datetime.datetime.strptime(timestamp, '%Y%m%d')
+        date_format = re.sub(  # Support %s on windows
+            r'(?<!%)(%%)*%s', rf'\g<1>{int(datetime_object.timestamp())}', date_format)
         return datetime_object.strftime(date_format)
     except (ValueError, TypeError, AttributeError):
         return default