Resize Composition to Selected Layers in After Effects

When working with Adobe After Effects, you may sometimes need to resize a composition to match the bounding box of selected layers and center them within the resized composition. Performing this manually can be time-consuming, especially in projects with multiple layers. This script automates the entire process, making your workflow much more efficient.

Script Overview

This script resizes the active composition to the exact bounding box of the selected layers, ensuring the layers are centered within the resized composition. It calculates the boundaries of the selected layers, adjusts the composition’s width and height, and shifts the layers’ positions to maintain their placement relative to the new comp center.

How It Works

1. Checks for Active Composition and Selected Layers:
   • Ensures that the active item is a composition and that at least one layer is selected. If not, it displays an alert.
2. Calculates the Bounding Box:
   • Iterates through the selected layers to determine the minimum and maximum x and y coordinates of their bounding boxes.
3. Adjusts Composition Dimensions:
   • Updates the composition’s width and height to match the bounding box.
4. Centers the Layers:
   • Calculates the offset required to center the layers within the resized composition and applies the necessary adjustments.

Using the Script

Here’s how you can use the script in After Effects:

1. Prepare Your Project:
   • Open your After Effects project and select a composition.
   • Select the layers you want the composition to resize around.
2. Save the Script:
   • Copy the provided code and save it as a .jsx file, such as ResizeCompToSelection.jsx.
3. Run the Script:
   • In After Effects, go to File > Scripts > Run Script File... and choose your script file.
4. Results:
   • The composition is resized to fit the selected layers’ bounding box.
   • The selected layers are centered in the resized composition.

Code Highlights

Checking the Active Composition

var comp = app.project.activeItem;

if (!(comp && comp instanceof CompItem)) {
    alert("Please select a composition.");
    return;
}

This ensures that the active item is a composition; if not, the script displays an alert.

Calculating the Bounding Box

var layerBounds = layer.sourceRectAtTime(comp.time, false);
var layerPosition = layer.position.value;

var layerMinX = layerPosition[0] - layerBounds.width / 2;
var layerMaxX = layerPosition[0] + layerBounds.width / 2;
var layerMinY = layerPosition[1] - layerBounds.height / 2;
var layerMaxY = layerPosition[1] + layerBounds.height / 2;

minX = Math.min(minX, layerMinX);
maxX = Math.max(maxX, layerMaxX);
minY = Math.min(minY, layerMinY);
maxY = Math.max(maxY, layerMaxY);

This part calculates the minimum and maximum x and y coordinates for the bounding box.

Resizing the Composition and Centering Layers

comp.width = Math.round(newWidth);
comp.height = Math.round(newHeight);

var offsetX = newCompCenterX - boundingBoxCenterX;
var offsetY = newCompCenterY - boundingBoxCenterY;

selectedLayer.position.setValue([
    selectedLayer.position.value[0] + offsetX,
    selectedLayer.position.value[1] + offsetY
]);

This updates the composition’s dimensions and centers the selected layers based on the calculated offsets.

Benefits of the Script

• Efficiency: Automates resizing and centering tasks, saving time.
• Precision: Ensures the composition matches the exact dimensions of the selected layers.
• Ease of Use: Minimal setup required—just select layers and run the script.