TASK 64 slice F — the two things left after the feature worked by hand.
- App Settings → **Video clips → Auto Green/Blue Screen** (off by default). When on, a
high-confidence detected screen is keyed as soon as the clip is added; the panel says
"Removed automatically" so an automatic change is never silent. Medium confidence still
asks, low says nothing — a wrong automatic key eats the picture.
- **A clip is a clip:** the alert box's own replacement clip keys through the same settings
block (one alert box per layout, so its settings are the ones the next alert uses), and
choosing an alert clip runs the same detector. The Green/Blue Screen panel now appears for
a video layer *or* an alert box with a custom clip (`Source.ShowsChromaKey`).
- Spill ships as the creator-facing **Fringe** switch; nothing further to tune behind it.
Test: `ChromaKeyApplyTests` gains the auto-apply case (no click, still explicit in the panel)
and an alert-clip case (its pipe asks ffmpeg for colorkey+despill with the blue screen type).
Docs: TASK 64 complete in TASKS.md, known limits recorded in the task file, HANDOFF rewritten.
verify.sh: 546 passed, 0 failed, 0 warnings.
TASK 64 slices D and E: the feature is usable end to end.
- Add a video file → one frame is probed (new `IChromaProbe`/`FfmpegChromaProbe`, one ffmpeg
pass at 160x90, off the UI thread) and the layer gets an offer: "Looks like a green screen —
Remove it", with the measured colour as a swatch.
- Accepting it turns the offer into settings (Amount / Softness / Fringe) that reach ffmpeg as
`colorkey` + `despill` + `format=bgra`, so the key is computed in the pipe and both consumers
(the shared preview bitmap and the compositor's frame) carry the same alpha.
- Media sessions are now keyed by **path + look** (`MainViewModel.MediaSessionKey`), so two
layers with the same settings still share one decoder, and changing the look releases the old
session and starts the new one. Removal, load reconciliation, loop and audio settings all move
to the same key.
- Settings persist on the `Source` row (six ALTER TABLE guards + SELECT/INSERT), so a keyed layer
comes back keyed.
- Panel section is plain creator words: Green/Blue Screen, Amount, Softness, Fringe.
Test: `ChromaKeyApplyTests` — the pipe asks ffmpeg to key (and does not when off); a green-screen
clip is offered, accepting it starts a keyed session, the layer's resolver then reads that session
rather than the old one; the setting survives a save.
Docs: TASK 64 D/E ticked with slice F (auto-apply setting + alert clips) left open; frame-pipeline
records the decode-option design; HANDOFF rewritten. verify.sh: 544 passed, 0 failed, 0 warnings.
TASK 64 units B and C — the two pure halves, no wiring yet.
- `Services/ChromaKeyDetector.cs`: samples the frame's outer ring (the screen is at the
edges, the subject in the middle), reports Green/Blue/None plus the colour actually shot
and a confidence. Confidence is coverage × hue tightness, which is what keeps a lawn or
a football pitch from being offered as a keyable screen. Letterbox bars are excluded from
the denominator rather than counted against the screen. Never decides anything: an offer
is the creator's to accept.
- `Services/VideoFilterChain.cs`: options → `-vf` (scale → colorkey → despill → format=bgra)
plus a `Signature` so two layers keyed identically can share one decoder. Numbers clamp and
an unparseable colour falls back to the app default, so ffmpeg is never handed a filter it
rejects at spawn.
- Keying is done by the bundled ffmpeg, not by us: verified against the shipped binary that
`colorkey=…,format=bgra` emits straight-alpha BGRA (alpha 0 on keyed pixels), which is what
the compositor already blends. No per-pixel loop lands in the 16.67 ms render budget.
Test: `ChromaKeyDetectorTests` — green, blue, letterboxed, lawn (must say None), mixed scene,
dark frame, plus the chain strings and signature sharing.
Docs: TASK 64 queued in TASKS.md with its slice table; the decisions.md chroma-key reversal
recorded as a reversal (it was buried for webcam background removal, not for supplied clips).
gramps