Step 1: Project Setup

Open After Effects

Create a New Project

Go to Composition > New Composition

Name: GreenScreenComp

Size: 1920x1080

Frame Rate: 30

Duration: As needed

Step 2: Import Your Green Screen Clip

Drag your video clip with green background into the Project Panel

Drag it to your timeline

Step 3: Apply Keylight Effect

Select your video layer in the timeline

Go to Effects & Presets (right panel)

Search for: Keylight (1.2)

Drag & drop Keylight onto your video layer

Step 4: Remove Green Background

In the Effect Controls Panel, you'll see Keylight options

Click the eyedropper tool next to “Screen Colour”

Click anywhere on the green background in your video

The green should disappear and the background turns black (transparent)

Step 5: Clean the Edges (Optional but Recommended)

Scroll down to Screen Matte → Click to expand

Adjust:

Clip Black: 10-15%

Clip White: 85-90%

Use Screen Shrink/Grow and Softness to clean edges

Step 6: Add Your New Background

Import a background image or video

Drag it below your keyed video layer in the timeline

Step 7: Export the Final Video

Go to File > Export > Add to Render Queue

In Render Queue:

Format: QuickTime / H.264 (via Media Encoder)

Choose location and export