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Key Mix

Key Mix · screenshot coming soon

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What this node does

Key Mix blends two videos using a mask: video A goes over video B wherever the mask is white. It’s the classic mix/merge stage of a keying pipeline — after you pull a matte with a keyer, Key Mix uses that matte to lay the foreground onto a background. You choose how the alpha is combined (compositing operation) and how strongly the whole mix is applied. Inputs and output are COMFYTV_VIDEO (the mask can be a COMFYTV_VIDEO matte or a COMFYTV_IMAGE still). It has a ▶ Run. Both video A, video B, and a mask are required — the node errors if any is missing.

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When to use it

  • You keyed a subject and now want it composited over a new background clip.
  • You have a matte (from Keyer/PIK/Select0r or a mask image) and two layers to merge.
  • You need a specific alpha operation (over/add/subtract/max/min) between the layers.

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Parameters

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mix

Overall strength of the mix. Range 0.0–1.0, default 1.0. At 1.0 the mask fully drives the blend; lower it to dissolve the effect back toward B.

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invert_mask

When on, flips the mask so white becomes the area that shows B instead of A. Default off. Use it when your matte is the wrong way round.

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alpha_op

How A’s alpha combines with the composite: over (default), add, subtract, max, or min. over is standard compositing; the others are useful for combining mattes or additive effects.

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Inputs (all required except as noted)

  • video_a — the foreground, placed where the mask is white.
  • video_b — the background, shown where the mask is black.
  • mask_video — a matte video, or…
  • mask — a still mask image (used if no mask video is wired).

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Outputs

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Tips

  • White mask = show A; if your foreground and background look swapped, toggle invert_mask.
  • A keyer’s matte output plugs straight into mask_video.
  • To interoperate with native ComfyUI nodes, insert a Bridge. See bridges.md.
  • Chroma Key / Keyer / PIK Keyer / Select0r — produce the matte Key Mix consumes.
  • Matte Morphology — clean up the matte edges before mixing.