Create VP9 Alpha WebM from a Chroma-Screen Source

Use the source video's RGB as the output RGB. Generate its matte independently per frame; never copy a matte from a reference asset or reuse a previous frame's mask. Produce a final asset only with an approved production layout profile.

Preconditions

• Require a green-screen or blue-screen source with visible screen colour around the outer frame border.
• Stop if the border is not identifiable as a chroma screen, or if critical foreground detail is intentionally near the screen colour and needs manual rotoscoping.
• Preserve the source display frame rate (avg_frame_rate), not its nominal container rate.
• Require an approved layout profile for final delivery. The profile must declare the role's 1488×1488 or 2320×2320 canvas, scale, and top/left padding. See references/layout-profile.schema.json for its shape.

Repair

Run:

python scripts/transfer_greenscreen_alpha.py <screen-source.mp4> <transparent.webm> --layout-json <ffmpeg_params.json> --role <role-key>