StableKey Docs

StableKey is an API-first service for VFX-grade green-screen unmixing. Inputs are StableUpload public URLs; outputs land at agent-reserved StableUpload slots as mp4s (alpha matte, straight foreground, and premultiplied RGBA).

The model is CorridorKey by Niko Pueringer / Corridor Digital — used here under permission, run at cost-plus-defensive-buffer (no profit margin).

Workflow

1. Upload your RGB plate to StableUpload.
2. Reserve 3 output slots on StableUpload (do NOT upload bytes — forward the URLs to stablekey).
3. POST the slots + your declared frame count/resolution to /api/process.
4. Poll /api/jobs/{jobId} until status is complete or failed.

Hint generation

Default: stablekey runs a fast chroma-key inline. For clean studio plates this is empirically equivalent to SAM 3.1 hints. Bring your own SAM-derived hintUrl only for "gnarly" shots: subject in green clothing, busy non-green BG props, multiple subjects, translucent FG, or visible tracking-dot crosses.

Pricing

Cost is hint-based at quote time, validated by ffprobe on the worker side. Empirical: 250-frame 1080p ≈ $0.10, 250-frame 4K ≈ $0.15. Floor $0.05/video, $0.03/image. 2× defensive markup is documented in the plan and reinvested, not extracted as profit.

Full guidance

Agent-friendly llms.txt is served at /.well-known/llms.txt.