refactor(main.py): optimize frame advancement logic to handle playback speed and improve readability

croppa/main.py

@@ -311,22 +311,34 @@ class VideoEditor:
         self.load_current_frame()
 
     def advance_frame(self) -> bool:
-        """Advance to next frame - optimized to avoid seeking"""
+        """Advance to next frame - optimized to avoid seeking, handles playback speed"""
         if not self.is_playing:
             return True
 
-        self.current_frame += 1
-        if self.current_frame >= self.total_frames:
-            self.current_frame = 0  # Loop - this will require a seek
+        # Calculate how many frames to advance based on speed
+        # For speeds > 1.0, we skip frames. For speeds < 1.0, we delay in main loop
+        frames_to_advance = max(1, int(self.playback_speed))
+        
+        new_frame = self.current_frame + frames_to_advance
+        if new_frame >= self.total_frames:
+            new_frame = 0  # Loop - this will require a seek
+            self.current_frame = new_frame
             return self.load_current_frame()
 
-        # For sequential playback, just read the next frame without seeking
-        ret, frame = self.cap.read()
-        if ret:
-            self.current_display_frame = frame
-            return True
+        # For sequential playback at normal speed, just read the next frame without seeking
+        if frames_to_advance == 1:
+            ret, frame = self.cap.read()
+            if ret:
+                self.current_frame = new_frame
+                self.current_display_frame = frame
+                return True
+            else:
+                # If sequential read failed, fall back to seeking
+                self.current_frame = new_frame
+                return self.load_current_frame()
         else:
-            # If sequential read failed, fall back to seeking (might be end of file or codec issue)
+            # For speed > 1.0, we need to seek to skip frames
+            self.current_frame = new_frame
             return self.load_current_frame()
 
     def apply_crop_zoom_and_rotation(self, frame):