fix: update progress bar accuracy for VFR

Author: nathanmdan

scenedetect/scene_manager.py

@@ -571,6 +571,7 @@ def detect_scenes(
         )
         decode_thread.start()
         frame_im = None
+        prev_position = None
 
         logger.info("Detecting scenes...")
         try:
@@ -581,13 +582,22 @@ def detect_scenes(
                 if next_frame is not None:
                     frame_im = next_frame
                 assert frame_im is not None
+                if prev_position is None:
+                    prev_position = self._start_pos
+                assert prev_position is not None
                 new_cuts = self._process_frame(position, frame_im, callback)
                 if progress_bar is not None:
                     if new_cuts:
                         progress_bar.set_description(
                             PROGRESS_BAR_DESCRIPTION % len(self._cutting_list), refresh=False
                         )
-                    progress_bar.update(1 + frame_skip)
+                    # Increment progress bar by delta of position.frame_num instead of 1
+                    # to handle VFR video where frame count is an approximation.
+                    # First frame increments by 1 as base case.
+                    delta_pos = position.frame_num - prev_position.frame_num
+                    is_first_frame = position.frame_num == 0
+                    progress_bar.update((1 if is_first_frame else delta_pos) + frame_skip)
+                    prev_position = position
         finally:
             if progress_bar is not None:
                 progress_bar.set_description(