heygen-com--hyperframes/skills/hyperframes-animation/adapters/css-animations.md

name, description

name	description
hyperframes-css-animations	CSS animation adapter patterns for HyperFrames. Use when authoring CSS keyframes, animation-delay based timing, animation-fill-mode, animation-play-state, or CSS-only motion that HyperFrames must seek deterministically during preview and rendering.

CSS Animations for HyperFrames

HyperFrames can seek CSS keyframe animations through its css runtime adapter. Use this for simple repeated motifs, background motion, shimmer, glow, masks, and non-sequenced decoration.

For scene choreography, GSAP is usually clearer. CSS animations work best when the motion belongs to one element and has a fixed duration.

Contract

• Put the animated element in the DOM before runtime initialization finishes.
• Give timed elements a data-start value so local animation time matches the clip.
• Use finite animation-duration and animation-iteration-count because the negative-delay fallback cannot represent unbounded duration in environments without WAAPI-backed CSS animations.
• Prefer animation-fill-mode: both so seeked states hold before and after active motion.
• Avoid wall-clock JavaScript, hover-triggered state, and class toggles that depend on user events.

The adapter discovers elements with computed animation-name, seeks their browser Animation handles when available, and falls back to pausing with negative animation-delay.

Basic Pattern

<div
  id="pulse-ring"
  class="clip pulse-ring"
  data-start="0"
  data-duration="4"
  data-track-index="2"
></div>

<style>
  .pulse-ring {
    width: 280px;
    height: 280px;
    border: 4px solid rgba(255, 255, 255, 0.7);
    border-radius: 50%;
    animation-name: pulse-ring;
    animation-duration: 1200ms;
    animation-timing-function: cubic-bezier(0.2, 0, 0, 1);
    animation-iteration-count: 3;
    animation-fill-mode: both;
  }

  @keyframes pulse-ring {
    from {
      opacity: 0;
      transform: scale(0.82);
    }
    35% {
      opacity: 1;
    }
    to {
      opacity: 0;
      transform: scale(1.18);
    }
  }
</style>

Stagger Pattern

Use CSS custom properties to avoid duplicating keyframes:

<div class="clip dots" data-start="1" data-duration="3" data-track-index="3">
  <span style="--i: 0"></span>
  <span style="--i: 1"></span>
  <span style="--i: 2"></span>
</div>

<style>
  .dots span {
    display: inline-block;
    width: 18px;
    height: 18px;
    margin-right: 10px;
    border-radius: 50%;
    background: currentColor;
    animation: dot-pop 900ms ease-out both;
    animation-delay: calc(var(--i) * 120ms);
  }

  @keyframes dot-pop {
    from {
      opacity: 0;
      transform: translateY(18px) scale(0.75);
    }
    to {
      opacity: 1;
      transform: translateY(0) scale(1);
    }
  }
</style>

Good Uses

• Decorative loops with a known repeat count.
• Mask, glow, shimmer, grain, and subtle parallax layers.
• Simple one-element entrances where a full JS timeline would be excessive.

Avoid

• Infinite CSS animations unless you have verified the browser exposes seekable WAAPI-backed CSS animation handles. Prefer a finite iteration count covering the visible duration. If you do use infinite, add data-duration to the root element — see Composition Duration below.
• Animating layout properties like top, left, width, or height when transforms work.
• Relying on hover, focus, scroll, or media queries to trigger render-critical motion.
• Changing animation classes after startup unless another deterministic timeline controls that change.

Composition Duration

The render engine needs to know the composition's total length. GSAP timelines report this automatically; CSS-only compositions have no timeline object, so the runtime infers duration from the longest running animation's computed end time (animation-delay + animation-duration × finite animation-iteration-count, per element with data-start added as an offset). data-duration on the root element is optional whenever every CSS animation on the page is finite — you don't need to add it just because the composition is CSS-driven.

animation-iteration-count: infinite (or any unresolved/unbounded animation) has no finite end time, so it cannot be auto-inferred. If the composition's only animation is infinite, you must add data-duration="<seconds>" to the root [data-composition-id] element with your intended total length — npx hyperframes lint errors on this case (root_composition_missing_duration_source) precisely because there is nothing for the runtime to infer.

<div
  data-composition-id="root"
  data-start="0"
  data-duration="6"
  data-width="1920"
  data-height="1080"
>
  <div class="clip spinner" data-start="0" style="animation: spin 1s linear infinite"></div>
</div>

Validation

After editing CSS animation compositions:

npx hyperframes lint
npx hyperframes check

Credits And References

• HyperFrames adapter source: packages/core/src/runtime/adapters/css.ts.
• Duration auto-inference: packages/core/src/runtime/init.ts (resolveAdapterDurationFloorSeconds), getInferredDurationSeconds in the adapter above.
• MDN CSS animation documentation: https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Properties/animation
• MDN animation-fill-mode: https://developer.mozilla.org/en-US/docs/Web/CSS/animation-fill-mode