fixed file naming thingy

tests/test_extension_case_normalization.py

@@ -52,6 +52,13 @@ class TestExtensionNormalization:
             (".JPEG", ".jpeg"),
             (".PNG", ".png"),
             (".GIF", ".gif"),
+            # Test extensions without dots (common from yt-dlp)
+            ("JPG", ".jpg"),
+            ("JPEG", ".jpeg"),
+            ("MP4", ".mp4"),
+            ("WEBM", ".webm"),
+            ("mp4", ".mp4"),
+            ("gif", ".gif"),
         ]
 
         for input_ext, expected in test_cases: