Source Text – Expression in Adobe After Effects: Step-by-Step Guide

The Source Text expression in Adobe After Effects allows you to dynamically control and animate the text in a layer using JavaScript-based expressions. This is useful for countdowns, typing effects, random text generation, and dynamic data-driven animation.

---

🧠 What is Source Text?

Source Text refers to the actual content of a text layer. Using expressions, you can change the text automatically over time or based on certain values.

---

🔧 How to Add a Source Text Expression

1. Create a Text Layer
   Go to Layer > New > Text and type anything.

2. Open the Expression Field

   • Press UU to reveal all modified properties, or simply open the text layer's properties.

   • Hold Alt (Windows) or Option (Mac) and click the Stopwatch next to Source Text.

3. Type Your Expression
   Enter the expression in the provided field.

---

🧪 Common Source Text Expressions

1. 🔢 Dynamic Number Counter

count = time * 10;
Math.floor(count)

📌 This will animate the text to count up from 0 by 10 units per second.

---

2. 🧮 Countdown Timer (Seconds)

startTime = 10;
count = Math.floor(startTime - time);
"Countdown: " + count

📌 Counts down from 10.

---

3. 🎰 Random Text Generator

chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
result = "";
for (i = 0; i < 5; i++) {
  result += chars.charAt(Math.floor(Math.random() * chars.length));
}
result

📌 Changes to a random 5-character text every frame.

---

4. ✍️ Typing Effect

fullText = "Welcome to Learnoy!";
chars = Math.floor(time * 10);
fullText.substr(0, chars)

📌 Text will appear letter by letter like typing.

---

🧷 Tips and Tricks

• Use Math.floor() to get whole numbers.

• Concatenate strings using + operator.

• You can link to other layer values using thisComp.layer("LayerName").text.sourceText.

---

✅ Use Cases

• Dynamic text changes without keyframes.

• Clock, countdowns, scoreboards.

• Simulate digital boards, typing, or hacking effects.

• Automate text changes via scripts or sliders.

---

🏁 Final Thoughts

Using Source Text expressions in After Effects makes your animations smarter and more interactive. With just a few lines of code, you can turn static text into dynamic motion elements.