`chroma_key`

Removes a chroma key background and outputs a transparent QuickTime RLE/ARGB file. Subsequent edit decisions reference the keyed file automatically.

Tip: The edit processor can also remove a background with its remove_background operation, and can chain it with other adjustments in a single step. Use edit when you want to combine several adjustments; this processor remains available and unchanged.

When to use

Use when your source footage was filmed against a green or blue screen. Run before placing the footage on the timeline; chroma_key substitutes the source file in all downstream edit decisions.

In the editor

Add it from the Library (Transforms group), or with + add step and a search for chroma_key.

Under Inputs, add source: a file input for the footage you shot against the screen, or a step input to key only the parts an earlier step kept, which is quicker because the rest of the file is never touched. color is a color swatch, set to the shade of your screen rather than a textbook green. If the edges come out ragged, raise similarity a little; blend softens them. The remaining controls are behind Show advanced.

It creates no clips, so the run timeline is unchanged. What changes is that the background is gone wherever that footage appears, and whatever sits on a lower level shows through. Set your levels up so there is something behind it, or you will key a subject onto black.

YAML Example

- id: key
  processor: chroma_key
  input:
    - id: source
      file: speaker-footage
  params:
    color: "0a7c47"     # hex without #
    similarity: 0.10
    blend: 0.05
    hole_fill: 1
  cache: true

Inputs

ID	Source	Description
`source`	file or step	Source footage, or edit decisions referencing a source

Params

Param	Type	Default	Description
`color`	color	`"00ff00"`	Hex color to remove (without `#`)
`similarity`	number	`0.1`	Color distance threshold (0–1). Increase if edges are rough.
`blend`	number	`0.05`	Edge softness (0–1)
`hole_fill`	number	`1`	Morphological closing passes to fill interior holes
`scale`	string	`"project"`	Resolution to key at. `"project"` matches your project's output width and is by far the fastest option on 4K source. Leave it empty to key at the source resolution, or give an explicit size such as `"1920:-2"`.

Output

SourceRemaps: substitutes the original source file path with the keyed output file in all downstream edit decisions.

Notes

When input is a step (edit decisions), only the referenced segments are processed and concatenated; faster than processing the full file.
The keyed clip keeps a lossless transparency channel, so compositing it over b-roll or a background does not soften the edges.
A keyed clip is reused until the source file or one of the parameters changes.