diff --git a/Video2Crops.py b/Video2Crops.py
index 41504c8..9abbed1 100644
--- a/Video2Crops.py
+++ b/Video2Crops.py
@@ -234,6 +234,11 @@ def process_video(video_filenames, main_window):
     
     def check_duplicate(ref_frame, frame):
         global first_frame
+
+        min_possible_mse = 0
+        # Calculate the maximum possible MSE (when images are completely different)
+        max_possible_mse = 255**2 * roi_size * roi_size
+
         if duplicate_threshold > 0 and not first_frame:
             frame_is_duplicate = True
             # Calculate the Absolute Difference between the frames
@@ -241,16 +246,23 @@ def process_video(video_filenames, main_window):
 
             # Calculate the Mean Squared Error (MSE) between the frames
             mse = np.mean(frame_diff)
+            normalized_mse = 100 * (1 - (mse - min_possible_mse) / (max_possible_mse - min_possible_mse))
 
-            if mse > duplicate_threshold:
+            if normalized_mse > duplicate_threshold:
                 # The frame is significantly different, store it
                 ref_frame = frame.copy()
                 # Process the frame here or store it for later processing
                 frame_is_duplicate = False
 
+            debug('DEBUG', f"Frame is duplicate: {frame_is_duplicate}, MSE: {mse}, Normalized MSE: {normalized_mse}")
             return frame_is_duplicate, mse, ref_frame
         else:
-            return False, 0000, frame
+            if first_frame:
+                debug('DEBUG', f"Frame is the first frame, storing as initial reference")
+                first_frame = False
+            else:
+                debug('DEBUG', f"First Frame Duplicate check is disabled, ignoring!")
+            return False, 0, frame
 
     corner1 = (-1, -1)
     corner2 = (-1, -1)
@@ -390,13 +402,13 @@ def process_video(video_filenames, main_window):
         cv2.destroyAllWindows()
         debug('DEBUG', f"Destroyed all current CV2 windows")
         write_log(f"Video2Crops run complete!\nSaved {counter} frames.\nDiscarded {discarded_frames} frames.")
-        first_frame = False
     processing = False
 
 # Create a function to add files to the selected files Listbox
 def add_files():
+    global processing_button
     selected_files = selected_files_listbox.get(0, tk.END)
-    file_paths = filedialog.askopenfilenames(filetypes=[("Video Files", "*.mp4 *.avi *.mov")])
+    file_paths = filedialog.askopenfilenames(title='Select Video File(s)', filetypes=[("Video Files", FILE_TYPES)])
     if file_paths:
         for file_path in file_paths:
             if file_path not in selected_files:
@@ -404,17 +416,26 @@ def add_files():
                 debug('DEBUG', f"Queued video file: {file_path}")
             else:
                 debug('DEBUG', f"Attempted to queue already-queued file \'{file_path}\'")
+    selected_files = selected_files_listbox.get(0, tk.END)
+    if len(selected_files) > 0:
+        processing_button.config(state='normal')
 
 # Create a button to remove the selected file from the Listbox
 def remove_file():
+    global processing_button
     selected_index = selected_files_listbox.curselection()
     if selected_index:
         selected_files_listbox.delete(selected_index)
         debug('DEBUG', f"Removed file from queue: {selected_index}")
+    selected_files = selected_files_listbox.get(0, tk.END)
+    if len(selected_files) <= 0:
+        processing_button.config(state='disabled')
 
 # Create a function to clear the queue
 def clear_queue():
+    global processing_button
     selected_files_listbox.delete(0, tk.END)
+    processing_button.config(state='disabled')
     debug('DEBUG', f"Cleared the queue")
 
 # Create a function to cancel processing
@@ -448,25 +469,29 @@ def process_files():
 # Define dynamic process/cancel button
 def process_cancel_toggle():
     debug('DEBUG', f"Toggling process/cancel button state")
-    global processing, processing_thread, processing_button_state, selected_files
-    if processing_button_state == "start":
-        if not processing:
-            processing = True
-            selected_files = selected_files_listbox.get(0, tk.END)
-            processing_thread = threading.Thread(target=process_video, args=(selected_files, root))
-            processing_thread.daemon = True
-            processing_thread.start()
-            processing_button.config(text="Cancel")
-            processing_button_state = "cancel"
-    elif processing_button_state == "cancel":
-        if processing:
-            processing = False
-            if processing_thread.is_alive():
-                processing_thread.join()
-            processing_button.config(text="Process Files")
-            processing_button_state = "start"
+    global processing, processing_thread, selected_files
+    if not processing:
+        toggle_process_button(False)
+        processing = True
+        selected_files = selected_files_listbox.get(0, tk.END)
+        processing_thread = threading.Thread(target=process_video, args=(selected_files, root))
+        processing_thread.daemon = True
+        processing_thread.start()
+    elif processing:
+        toggle_process_button(True)
+        processing = False
+        if processing_thread.is_alive():
+            processing_thread.join()
     debug('DEBUG', f"Processing/Cancel button state switch finished")
 
+async def toggle_process_button(enable=bool):
+    """True = Set state to 'Process Files' | False = Set state to 'Cancel'"""
+    global processing_button
+    if enable:
+        processing_button.config(text="Process Files")
+    else:
+        processing_button.config(text="Cancel")
+
 # Create a function to open the preferences window
 def open_preferences():
     debug('DEBUG', f"Opening preferences window")
@@ -647,7 +672,7 @@ remove_file_button = tk.Button(root, text="Remove File", command=remove_file)
 remove_file_button.pack(padx=20, pady=5)
 
 # Create a button to process the selected files
-processing_button = tk.Button(root, text="Process Files", command=process_cancel_toggle)
+processing_button = tk.Button(root, text="Process Files", command=process_cancel_toggle, state='disabled')
 processing_button.pack(padx=20, pady=5)
 
 debug('DEBUG', 'UI generated, running main loop')