Auto-Resizing Text Boxes Dynamically in After Effects: Save Time

When working with text animations in After Effects, manually adjusting background shapes to fit the text can be time-consuming and frustrating. Fortunately, there’s a way to make text boxes automatically resize based on the text content using expressions. This not only saves time but also ensures a dynamic and professional look for your animations.

In this guide, we’ll go step by step on how to create an auto-resizing text box in After Effects using expressions. By the end, you’ll be able to apply this technique to any text animation project with ease.

Step 1: Create a New Composition and Add Text

1. Open After Effects and create a new composition.
2. Set the dimensions to 1920x1080 and duration to 10 seconds.
3. Click the Text Tool (T) and type your desired text.
4. Adjust the font, size, and alignment as needed.
5. Use the Align Panel to center the text horizontally and vertically.

Step 2: Center the Anchor Point

For a clean and organized animation, ensure the Anchor Point is centered:

1. Select the Text Layer.
2. Press Ctrl + Alt + Home (Windows) / Cmd + Option + Home (Mac) to center the Anchor Point within the text.
3. Use the Align Panel again to recenter the text.

Step 3: Create a Shape Background

1. Deselect all layers.
2. Select the Rectangle Tool (Q) and draw a shape behind your text.
3. Adjust the shape’s fill color and remove any stroke if necessary.
4. Move the Shape Layer below the text layer in the timeline.

Step 4: Link the Shape Size to the Text Automatically

To make the background resize dynamically, we’ll use an expression.

1. Expand the Shape Layer properties and go to Rectangle Path > Size.
2. Hold Alt (Windows) / Option (Mac) and click on the stopwatch icon next to Size.
3. In the Expression Editor, enter the following code:

s = thisComp.layer("YourTextLayerName");
w = s.sourceRectAtTime().width;
h = s.sourceRectAtTime().height;
[w, h]

4. Replace “YourTextLayerName” with the actual name of your text layer.
5. Click Enter to apply the expression.

Now, whenever you change the text content, the background automatically resizes to fit!

Step 5: Adjust the Padding

By default, the background may be too tight around the text. To add some padding:

1. Expand the Shape Layer properties.
2. Click Add > Offset Paths.
3. Increase the Offset value to add padding.

Step 6: Round the Corners (Optional)

For a softer look, you can round the corners of your shape:

1. Under Offset Paths, locate the Line Join option.
2. Set it to Round Join.

Step 7: Animate the Text and Background

Now that our text box resizes dynamically, let’s animate it.

Fade-In Effect

1. Select the Text Layer.
2. Press T to open the Opacity property.
3. Set a keyframe at 0% opacity at the start of the timeline.
4. Move a few frames forward and set it to 100%.

Slide-In Animation

1. Select both the Text Layer and Shape Layer.
2. Press P to open the Position property.
3. Move to frame 0, create a keyframe with the text off-screen.
4. Move forward in time and bring the text to its final position.

Step 8: Use It in Multiple Lines

For multi-line text, the method changes slightly.

1. Pre-compose the Text and Shape Layer by selecting both and pressing Ctrl + Shift + C (Windows) / Cmd + Shift + C (Mac).
2. Duplicate the pre-comp and update the text inside without affecting other instances.

By using this auto-resizing text box method, you can make your After Effects projects more efficient and professional. Whether you're creating lower-thirds, title screens, or social media animations, this technique will save you time and effort.