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This example demonstrates the simplest way to get started with Helios using standard CSS animations. No framework required - just vanilla JavaScript, HTML, and CSS.

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Overview

The basic animation example shows how to:
  • Initialize the Helios engine
  • Use CSS keyframes for animations
  • Sync animations with the document timeline
  • Create a composition ready for rendering

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Setup

1

Create the HTML structure

Start with a basic HTML file containing an element to animate:
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Simple Composition</title>
</head>
<body>
  <div class="animated-box"></div>
  
  <script type="module" src="./src/main.ts"></script>
</body>
</html>
2

Add CSS animations

Define your animation using standard CSS keyframes:
body {
  margin: 0;
  overflow: hidden;
  background-color: #eee;
}

.animated-box {
  width: 150px;
  height: 150px;
  background-color: #007bff;
  position: absolute;
  top: 50%;
  left: 50%;
  /* Initial state */
  transform: translate(-50%, -50%) scale(0.5);
  opacity: 0;

  /* Use standard CSS animation */
  animation: moveAndScale 5s linear forwards;
}

@keyframes moveAndScale {
  0% {
    opacity: 0;
    transform: translate(-50%, -50%) scale(0.5);
  }
  50% {
    opacity: 1;
  }
  100% {
    opacity: 1;
    transform: translate(calc(-50% + 50vw - 100%), -50%) scale(1);
  }
}
3

Initialize Helios

Set up the Helios engine with autoSyncAnimations enabled to automatically control CSS animations:
import { Helios } from '@helios-project/core';
import './style.css';

// Initialize Helios engine
const helios = new Helios({
  duration: 5,
  fps: 30,
  autoSyncAnimations: true
});

// Expose for the Player and debugging
(window as any).helios = helios;

// Enable external control (e.g. from Renderer)
helios.bindToDocumentTimeline();

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How it works

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Auto sync animations

By setting autoSyncAnimations: true, Helios automatically hijacks all CSS animations on the page and synchronizes them with the video timeline. This means:
  • CSS animations pause, play, and seek in sync with the video
  • Frame-perfect rendering is guaranteed
  • No manual animation control needed

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Document timeline binding

The bindToDocumentTimeline() method connects Helios to the browser’s document timeline, allowing external tools like the Helios Renderer to drive the animation playback.

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Key concepts

  • Duration: Total length of your composition in seconds
  • FPS: Frames per second for rendering (typically 30 or 60)
  • autoSyncAnimations: Automatically sync CSS animations with Helios timeline
  • bindToDocumentTimeline: Enable external control for rendering

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Complete example

View the complete source code in the simple-animation directory.

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Next steps

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