Snap between framings on the cut the source already made - #178
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Three of six camera switches in a shipped clip flashed to bare wall. Frame by
frame at 24fps the worst is a hard cut to wall at frame 73, two frames held on
it, then a five frame fade into the right framing: 209ms about 50 luma brighter
than either speaker.
The stitch pads every run by the dissolve length to give the dissolve somewhere
to happen, and that pad runs this run's crop over the next run's content. Over a
layout change the subject has already moved, so the pad is the wrong framing by
construction and the dissolve blends a correct frame into a wall. The subject
survives the pad only while the next centre is still inside this crop, half a
window either side. Here the widest boundary was 1167px against a 607px reach.
Past that reach the crop snaps between framings as a step function of time, in
the pass that was already cropping. A step expression rather than a part per run
joined end to end, because cutting and rejoining drifts: -t keeps the frame that
starts before the cut and each part's audio carries its own encoder padding,
measured at 61 to 100ms per part and 403ms across five runs, leaving the video
177ms short of its own audio. One pass has nothing to accumulate.
Boundaries then snap to the source's own cuts. Runs close at the first sample
that noticed a change and the sampler runs at about 12Hz, so a boundary sat up
to 83ms late and two frames of the old crop landed on the new layout. Those
frames were both the wall left in shot and a second scene change 83ms after the
source's own, and that pair read as clustered cuts, which pulled the transition
blur onto a cut that never needed it.
Measured against 2.7.6 on two ranges:
336-365s wall frames 6 -> 0 worst flash 209ms -> none
1100-1135s wall frames 8 -> 1 worst flash 209ms -> 42ms
edge energy near cuts 6.52 -> 7.85
Both keep their exact length and come out one frame shorter.
.venv joins .gitignore. The file had venv/ only, so a 202MB virtualenv at the
repo root was one git add -A away from being committed.
718 Python tests, 320 vitest.
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📝 WalkthroughWalkthroughThe video processor now detects source cuts, snaps mixed-layout run boundaries, and uses stepped crop rendering when framing changes exceed dissolve limits. Golden tests cover eligibility, crop expressions, and boundary snapping. ChangesMixed-layout crop processing
Development environment ignore rule
Estimated code review effort: 3 (Moderate) | ~25 minutes Merge Risk: 🔵 Low · up to The PR changes crop transitions and adds regression coverage; the remaining merge-readiness issue is localized lint violations in the test evaluator, so the change is mergeable with explicit owner follow-up to clean up those lines. Sequence Diagram(s)sequenceDiagram
participant video_processor.py
participant FFmpeg
participant dissolve_part_generation
video_processor.py->>video_processor.py: evaluate adjacent framing reach
alt Framings remain within the dissolve range
video_processor.py->>dissolve_part_generation: process dissolve parts
dissolve_part_generation-->>video_processor.py: return dissolve parts
else Framings exceed the dissolve range
video_processor.py->>FFmpeg: render bounded stepped crop
FFmpeg-->>video_processor.py: return cropped output
video_processor.py->>video_processor.py: assemble hard cuts
end
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Inline comments:
In `@tests/test_crop_path_golden.py`:
- Around line 488-491: Update the expression evaluator’s character-parsing logic
around the depth and parts handling to split each compound statement into
separate lines, eliminating Ruff E701 and E702 violations while preserving the
existing behavior.
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Three of six camera switches in a shipped clip flashed to bare wall. Frame by frame at 24fps, the worst one:
Why
The stitch pads every run by the dissolve length to give the dissolve somewhere to happen, and that pad runs this run's crop over the next run's content. Over a layout change the subject has already moved, so the pad is the wrong framing by construction and the dissolve blends a correct frame into a wall.
The subject survives the pad only while the next centre is still inside this crop, half a window either side. Here the widest boundary was 1167px against a 607px reach.
What it does instead
Past that reach the crop snaps between framings as a step function of time, in the pass that was already cropping.
A step expression rather than a part per run joined end to end, because cutting and rejoining drifts. Measured:
-tkeeps the frame that starts before the cut, and each part's audio carries its own encoder padding. That left the video 177ms short of its own audio, which is the drift class #175 was written to fix. One pass has nothing to accumulate.Boundaries then snap to the source's own cuts. Runs close at the first sample that noticed a change and the sampler runs at about 12Hz, so a boundary sat up to 83ms late and two frames of the old crop landed on the new layout. Those frames were both the wall left in shot and a second scene change 83ms after the source's own:
That 83ms pair read as clustered cuts, which pulled
_apply_local_transition_smoothingonto a cut that never needed it and cost 20% of the edge energy around it.Measured against 2.7.6
Edge energy near cuts on the second range: 6.52 → 7.85. Both clips keep their exact length and come out one frame shorter, from the
-tclamp taking the tail frame.Also
.venvjoins.gitignore. The file hadvenv/only, so a 202MB virtualenv at the repo root was onegit add -Afrom being committed.718 Python tests, 320 vitest, tsc clean.
Summary by CodeRabbit
Bug Fixes
Tests
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