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[bugfix] Fix progress bar accuracy for VFR videos #562

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[bugfix] Fix progress bar accuracy for VFR videos #562

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fix: update progress bar accuracy for VFR
nathanmdan Aug 3, 2026
8bf8c2a
Merge branch 'main' into main
Breakthrough Aug 8, 2026
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12 changes: 11 additions & 1 deletion scenedetect/scene_manager.py
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Original file line number Diff line number Diff line change
Expand Up @@ -571,6 +571,7 @@ def detect_scenes(
)
decode_thread.start()
frame_im = None
prev_position = None

logger.info("Detecting scenes...")
try:
Expand All @@ -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

@Breakthrough Breakthrough Aug 8, 2026

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position.frame_num == 0 won't hold when detection starts from a seek (e.g. start_time is set) leading to an off by 1 error in some cases. Both this and the frame_skip issue below can be fixed if we keep prev_position = None and computing:

delta = 1 if prev_position is None else position.frame_num - prev_position.frame_num
progress_bar.update(delta)
prev_position = position

The first frame counts as 1, and each later frame delta covers all of the skipped frames too (no special cases needed). This also avoids reading self._start_pos which is set on the decode thread.

progress_bar.update((1 if is_first_frame else delta_pos) + frame_skip)

@Breakthrough Breakthrough Aug 8, 2026

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When frame_skip > 0, the skipped frames are already reflected in position.frame_num. See the prev. comment for an alternative.

The decode thread queues a frame, then skips, so consecutive queued positions differ by frame_skip + 1). Adding + frame_skip on top double-counts them, e.g. with frame_skip=1 the bar advances 3 per processed frame instead of 2.

prev_position = position
finally:
if progress_bar is not None:
progress_bar.set_description(
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