Key and Fill

Key & Fill is a layer-level compositing feature. As the name suggests, it has two parts: the key — a layer whose content defines a transparency mask — and the fill — the cues that mask is applied to. This masks content through animated shapes, text cutouts, or grayscale mattes without modifying the source media.

Unlike Chroma Key, which keys a single cue on its own pixel colors, Key & Fill uses a separate layer as the mask source. Any content — video, images, text, or generated graphics — can serve as the mask.

Keying Mode
Key Content
Fill Content
Key Layer
+
Fill Layer
=
Result

How It Works

  • The key layer defines the mask. Its output is read either as luminance (Luma Key) or as alpha (Alpha Key), and each mode can be inverted. The key layer itself is not shown on the output.
  • The fill cue receives that mask, which turns parts of it transparent or opaque.

Luma Key works with any content, including video with no alpha channel, because it keys on brightness. Alpha Key suits content that already carries transparency, such as PNG images or ProRes 4444 video.

Configuring Key & Fill

Key & Fill is set up in two places:

  • Key side (the layer) — turn a layer into a key source and choose its mode in Layer Properties → Keying Layer. See Working with Layers.
  • Fill side (the cue) — enable Key & Fill on the cue you want to fill, with its Invert and Visualize Key options. See Adding Media Cues — Key and Fill.

Each side has a Channels selector with buttons 1–4, and more than one can be active. A key layer can render to several channels at once. A fill cue can read from several at once. The key and fill connect wherever their channels overlap. For example, one layer keys on channel 1 and another keys on channel 2, while a single cue fills from both. Independent Key & Fill pairs can also run side by side on separate channels.

Use Cases

  • Dynamic text reveals — text on the key layer cuts through video on the fill layer.
  • Shaped content windows — a white-on-black matte shows the fill only within the shape.
  • Creative transitions — animate the key content (an expanding circle, a moving gradient) to reveal or hide the fill over time.
Previous Next