feat(main.py): add safety checks for large videos to prevent excessive memory usage

main.py

@@ -490,11 +490,24 @@ class MediaGrader:
         if not self.is_video(self.media_files[self.current_index]):
             return
             
+        # Safety check for huge videos
+        safe_frame_count = max(1, int(self.total_frames * 0.6))
+        estimated_mb = safe_frame_count * 5 // 1024  # Rough estimate: 5MB per frame
+        
+        if safe_frame_count > 5000:  # ~3 minutes at 30fps
+            print(f"Video too large for preloading! {safe_frame_count} frames would use ~{estimated_mb}GB RAM")
+            print("Multi-segment mode not available for videos longer than ~3 minutes")
+            return
+        elif safe_frame_count > 1000:  # Warn for videos > ~30 seconds
+            print(f"Large video detected: {safe_frame_count} frames will use ~{estimated_mb}MB RAM")
+            print("Press any key to continue or 'q' to cancel...")
+            # Note: In a real implementation, you'd want proper input handling here
+            
         start_time = time.time()
         print(f"Setting up {self.segment_count} segments with video preloading...")
+        print(f"Will preload {safe_frame_count} frames (~{safe_frame_count * 5 // 1024}MB RAM)")
         
         try:
-            # Clean up existing segment captures
             print("Cleaning up existing captures...")
             self.cleanup_segment_captures()
             
@@ -514,10 +527,6 @@ class MediaGrader:
                 print("Error: Video has insufficient frames for multi-segment mode")
                 return
             
-            # Use conservative frame range
-            safe_frame_count = max(1, int(self.total_frames * 0.6))
-            print(f"Using safe frame count: {safe_frame_count} (60% of reported {self.total_frames})")
-                
             for i in range(self.segment_count):
                 if self.segment_count <= 1:
                     position_ratio = 0