feat(main.py): implement frame caching to improve playback performance

main.py

@@ -59,6 +59,10 @@ class MediaGrader:
         
         # Timeline visibility state
         self.timeline_visible = True
+        
+        # Simple frame cache for frequently accessed frames
+        self.frame_cache = {}  # Dict[frame_number: frame_data]
+        self.cache_size_limit = 50  # Keep it small and simple
 
         # Key repeat tracking with rate limiting
         self.last_seek_time = 0
@@ -558,6 +562,32 @@ class MediaGrader:
         self.segment_caps = []
         self.segment_frames = []
         self.segment_positions = []
+        # Clear frame cache
+        self.frame_cache.clear()
+
+    def get_cached_frame(self, frame_number: int):
+        """Get frame from cache or load it if not cached"""
+        if frame_number in self.frame_cache:
+            return self.frame_cache[frame_number]
+        
+        # Load frame and cache it (lazy loading)
+        if self.current_cap:
+            original_pos = int(self.current_cap.get(cv2.CAP_PROP_POS_FRAMES))
+            self.current_cap.set(cv2.CAP_PROP_POS_FRAMES, frame_number)
+            ret, frame = self.current_cap.read()
+            self.current_cap.set(cv2.CAP_PROP_POS_FRAMES, original_pos)
+            
+            if ret:
+                # Cache the frame (with size limit)
+                if len(self.frame_cache) >= self.cache_size_limit:
+                    # Remove oldest cached frame
+                    oldest_key = min(self.frame_cache.keys())
+                    del self.frame_cache[oldest_key]
+                
+                self.frame_cache[frame_number] = frame.copy()
+                return frame
+        
+        return None
 
     def update_segment_frames(self):
         """Update frames for all segments during playback"""
@@ -620,14 +650,20 @@ class MediaGrader:
                 segment_end = min(self.total_frames - 1, segment_start + segment_duration)
                 
                 target_frame = max(segment_start, min(current_frame + frames_delta, segment_end))
-                cap.set(cv2.CAP_PROP_POS_FRAMES, target_frame)
                 
-                # Load new frame
-                ret, frame = cap.read()
-                if ret:
-                    self.segment_frames[i] = frame
-                    # Reset position for next read
+                # Try cache first, then load if needed
+                cached_frame = self.get_cached_frame(target_frame)
+                if cached_frame is not None:
+                    self.segment_frames[i] = cached_frame
                     cap.set(cv2.CAP_PROP_POS_FRAMES, target_frame)
+                else:
+                    # Fall back to normal seeking
+                    cap.set(cv2.CAP_PROP_POS_FRAMES, target_frame)
+                    ret, frame = cap.read()
+                    if ret:
+                        self.segment_frames[i] = frame
+                        # Reset position for next read
+                        cap.set(cv2.CAP_PROP_POS_FRAMES, target_frame)
 
     def display_current_frame(self):
         """Display the current cached frame with overlays"""