diff --git a/main.py b/main.py
index b88f7d4..a332113 100644
--- a/main.py
+++ b/main.py
@@ -98,7 +98,8 @@ class MediaGrader:
 
     def is_video(self, file_path: Path) -> bool:
         """Check if file is a video"""
-        return file_path.suffix.lower() in self.extensions
+        video_extensions = [".mp4", ".avi", ".mov", ".mkv", ".gif"]
+        return file_path.suffix.lower() in video_extensions
 
     def calculate_frame_delay(self) -> int:
         """Calculate frame delay in milliseconds based on playback speed"""
@@ -122,8 +123,10 @@ class MediaGrader:
             self.current_cap.release()
 
         if self.is_video(file_path):
+            # Suppress OpenCV error messages for unsupported codecs
             self.current_cap = cv2.VideoCapture(str(file_path))
             if not self.current_cap.isOpened():
+                print(f"Warning: Could not open video file {file_path.name} (unsupported codec)")
                 return False
             self.total_frames = int(self.current_cap.get(cv2.CAP_PROP_FRAME_COUNT))
             self.current_frame = 0
@@ -364,13 +367,13 @@ class MediaGrader:
             destination = grade_dir / f"{stem}_{counter}{suffix}"
             counter += 1
 
+        # Track this move for undo functionality BEFORE making changes
+        self.undo_history.append((str(destination), str(current_file), self.current_index))
+
         try:
             shutil.move(str(current_file), str(destination))
             print(f"Moved {current_file.name} to grade {grade}")
 
-            # Track this move for undo functionality
-            self.undo_history.append((str(destination), str(current_file), self.current_index))
-
             self.media_files.pop(self.current_index)
 
             if self.current_index >= len(self.media_files):
@@ -382,6 +385,8 @@ class MediaGrader:
 
         except Exception as e:
             print(f"Error moving file: {e}")
+            # Remove the undo entry since the move failed
+            self.undo_history.pop()
 
         return True