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What is Video Compositing?

Video compositing combines visual layers into one sequence through masks, blending, transforms, keying, and effects. Its layers can include footage, graphics, text, animation, and generated imagery.

How Video Compositing works

Compositing evaluates a stack or graph of images at each output time, transforming every layer into a common frame before combining pixel values. Masks and mattes control coverage, blend operators determine how foreground and background interact, and keyers derive transparency from image content. The process is distinct from simple concatenation because layers overlap in space and time. It usually occurs during editing or rendering before the final delivery encode.

Key facts

  1. Confusing straight and premultiplied alpha changes edge colors during blending, commonly producing dark or bright fringes around keyed subjects and antialiased graphics.
  2. Many blend operations produce more physically plausible results in linear light; applying them directly to transfer-encoded values can create incorrect gradients and halos.
  3. Layers with different frame rates or time bases must be sampled on one output timeline, or animated elements and lip-synchronized overlays can drift or repeat unevenly.

When Video Compositing matters

Composite layers to add watermarks, lower thirds, picture-in-picture views, or replacement backgrounds. Complex effects and high-resolution inputs increase render cost and may expose mismatched color or timing.

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