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JamesandClaude Opus 4.6 915fe2f47a docs: improve quality based on Remotion/Stripe/Tailwind patterns
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Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
2026-03-23 23:57:01 +00:00

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---
title: Data Attributes
description: "Core attributes for controlling element timing and behavior."
---
Hyperframes uses HTML data attributes to control timing, media playback, and [composition](/concepts/compositions) structure. These are the declarative building blocks of every video.
## Timing Attributes
| Attribute | Example | Description |
|-----------|---------|-------------|
| `data-start` | `"0"` or `"intro"` | Start time in seconds, or a clip ID reference for [relative timing](#relative-timing) |
| `data-duration` | `"5"` | Duration in seconds. Required for images. Optional for video/audio (defaults to source duration). Not used on compositions. |
| `data-track-index` | `"0"` | Timeline track number. Controls z-ordering (higher = in front) and groups clips into rows. Clips on the same track cannot overlap. |
## Media Attributes
| Attribute | Example | Description |
|-----------|---------|-------------|
| `data-media-start` | `"2"` | Media playback offset / trim point in seconds. Default: `0` |
| `data-volume` | `"0.8"` | Audio/video volume, 0 to 1 |
| `data-has-audio` | `"true"` | Indicates video has an audio track |
## Composition Attributes
| Attribute | Example | Description |
|-----------|---------|-------------|
| `data-composition-id` | `"root"` | Unique ID for [composition](/concepts/compositions) wrapper (required on every composition) |
| `data-width` | `"1920"` | Composition width in pixels |
| `data-height` | `"1080"` | Composition height in pixels |
| `data-composition-src` | `"./intro.html"` | Path to external [composition](/concepts/compositions) HTML file |
## Element Visibility
Add `class="clip"` to all timed elements so the runtime can manage their visibility lifecycle:
```html index.html
<h1 id="title" class="clip"
data-start="0" data-duration="5" data-track-index="0">
Hello World
</h1>
```
## Relative Timing
Instead of calculating absolute start times, a clip can reference another clip's `id` in its `data-start` attribute. This means "start when that clip ends":
```html index.html
<video id="intro" data-start="0" data-duration="10" data-track-index="0" src="..."></video>
<video id="main" data-start="intro" data-duration="20" data-track-index="0" src="..."></video>
<video id="outro" data-start="main" data-duration="5" data-track-index="0" src="..."></video>
```
`main` resolves to second 10, `outro` resolves to second 30. If `intro`'s duration changes, downstream clips shift automatically.
### Offsets (Gaps and Overlaps)
Add `+ N` or `- N` after the ID to offset from the end of the referenced clip:
```html index.html
<!-- 2-second gap after intro -->
<video id="scene-a" data-start="intro + 2" data-duration="20"
data-track-index="0" src="..."></video>
<!-- 0.5-second overlap with intro (crossfade) -->
<video id="scene-b" data-start="intro - 0.5" data-duration="20"
data-track-index="1" src="..."></video>
```
<Note>
Overlapping clips must be on different tracks -- clips on the same track cannot overlap in time.
</Note>
<Accordion title="Relative timing rules and constraints">
**Same composition only** -- references resolve within the clip's parent [composition](/concepts/compositions). You cannot reference a clip in a sibling or parent composition.
**No circular references** -- A cannot start after B if B starts after A. The resolver detects cycles and throws an error.
**Referenced clip must have a known duration** -- either an explicit `data-duration` or a duration inferred from source media. If the referenced clip has no known duration, the reference cannot resolve.
**Parsing rules** -- if the value is a valid number, it is treated as absolute seconds. Otherwise it is parsed as one of:
- `<id>` -- start when that clip ends
- `<id> + <number>` -- start N seconds after that clip ends
- `<id> - <number>` -- start N seconds before that clip ends
**Chain length** -- references can chain (`A` -> `B` -> `C`), but deeply nested chains make the timeline harder to reason about. Keep chains under 3-4 levels for readability.
</Accordion>
## Next Steps
<CardGroup cols={2}>
<Card title="Compositions" icon="layer-group" href="/concepts/compositions">
How compositions use data attributes to define video structure
</Card>
<Card title="HTML Schema Reference" icon="book" href="/reference/html-schema">
Complete attribute reference with per-element details
</Card>
<Card title="GSAP Animation" icon="wand-magic-sparkles" href="/guides/gsap-animation">
Animate elements alongside data-attribute-driven timing
</Card>
<Card title="Common Mistakes" icon="triangle-exclamation" href="/guides/common-mistakes">
Pitfalls to avoid when setting up timing and attributes
</Card>
</CardGroup>