Fix unstable AI mask frames

The AI stability lane in the Refine mask dope sheet flags frames where the AI matte pops for a frame (flicker), loses most of the subject (drops out), or turns mushy (soft). You fix the first bad frame by hand and re-track from it. The re-track carries your corrected matte across the span with optical flow. It runs on your Mac and spends no credits.

The check compares each frame with its neighbours, so a subject moving fast is not flagged for moving.

Steps

1. Open Refine on the clip’s Object mask. Cask Film checks the AI mask straight away. The AI stability lane reads checking with a percentage, then either stable or an amber count such as 12 unstable.
2. With nothing selected, read the Stability section of the inspector. It names the flagged frames, the spans they form and the worst frame, for example 3 unstable frames in 2 spans · worst f7 (drops out).
3. Click an amber span on the AI stability lane. The span is selected and the playhead moves to its first frame. Drag on the lane instead to select a range of your own.
4. Press 3 for the Alpha view, or 2 for Overlay, to see what is wrong on this frame.
5. Fix this one frame. Paint with the Brush (B), or draw or adjust a shape. Paint stays on this frame only.
6. Click Re-track from f plus the frame number, at the right end of the transport bar. The bar shows Re-tracking with a percentage and a stop button.
7. Wait for the landing toast, for example AI re-track · f40–f62 · optical flow. The lane draws the landed pass as a strip with a pin on the frame you re-tracked from, and the stability check runs again.

The re-track starts from the matte as the Alpha view shows it on that frame: the AI mask, every layer and your paint together.

A newer pass wins over older ones where their ranges overlap.

When a re-track stops

A re-track that loses the subject stops before the bad frame instead of carrying a broken matte forward. The toast ends with lost the subject at f plus the frame, then fix it and re-track from there.

Cask Film moves the playhead to that frame and selects the rest of the span. Fix that frame and click Re-track from f again.

Undoing a re-track

• Press ⌘Z. A landed re-track is one undo step.
• Or click the landed pass on the AI stability lane to select it and press ⌫. The toast reads Removed AI re-track with its range.

Result

The AI stability lane shows a strip under each re-tracked span, and the amber count drops or the lane reads stable. Play the span with Space in the Alpha view to confirm the matte holds. Click Done to bake it into the Object mask.

If it doesn’t work

Symptom	Cause	Fix
No Re-track from f button	Nothing is selected on the AI stability lane	Click an amber span, or drag across the lane
The button is dimmed. Its tooltip says to move the playhead into the range	The playhead is outside the selected span	Move the playhead inside it. That frame is the one re-tracked from
Still reading the AI re-tracks · try again in a moment	Refine is still loading earlier passes from the project	Wait a moment and click again
Nothing to re-track on this frame	The matte on this frame is under 50% everywhere	Paint or draw the subject on this frame first
Re-track lost the subject right after a frame	The pass could not hold the subject even one frame on	Fix the frame the toast names and re-track from it
Edges drift over a long span of fast motion, such as hair or limbs	Optical flow drifts over long, deforming spans	Re-track shorter spans, and fix a frame partway through before re-tracking from it