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Image fetch and display optimization on the landing page (LCP 404 ms → poster priority, sizing, caching)

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Avaliação

Dificuldade
4/5
Tempo estimado
3-5 dias
Facilidade para iniciantes
35/100
Tipo de issue
Refatoração
Clareza
Razoavelmente clara
Status de atividade
Ativa
Stack de tecnologia
html, javascript
Domínio
frontend, performance

Direção de pesquisa

Start in website/site/src/components/FilmScreen.astro where the hero video poster and attributes are set, then check Base.astro for a possible preload and the inline module in the built index.html. Caching needs a new website/site/public/_headers file and wrangler.jsonc, and the poster resizing belongs in the pnpm run media pipeline under website/hero-animation/. Done means the acceptance checklist holds: High poster priority in DevTools, a smaller poster on a 1318×741 viewport, Cache-Control on /media/*, and LCP under 300 ms.

Escrita pelo modelo de indexação a partir do texto da issue.

Descrição

Website
Context

LCP analysis of ema.tnsor.network (measured 2026-10-16): LCP is the hero <video>'s poster frame (/media/hero-poster.webp), landing at 404 ms with a 312 ms render delay after the image finishes downloading (~92 ms). Full diagnostics:

Metric / Attribute Value Finding
LCP Timing 404 ms Total render delay is 312 ms.
Image Priority Medium Failed fetchpriority=high check.
Resolution 1920×1080 Oversized for the 1318×741 display area.
Potential savings 39.1 KB Oversized resolution wastes bytes.
Cache policy max-age=0 Forces re-validation on every request.

Render delay breaks down to a ~205 ms layout task plus script execution (line 19, col 5131 — inline module in the built index.html) competing with the poster's first paint.

Current markup (FilmScreen.astro)
<video muted loop playsinline preload="auto" poster={poster} data-autoplay data-low-src={lowSrc} aria-label={title}>

No fetchpriority, no responsive source, and Cloudflare Workers static assets currently emit no cache headers (no _headers file; wrangler.jsonc assets.directory only).

Recommendations
  • Elevate resource priority — fetchpriority="high" on the video (applies to the poster fetch). Optionally add a <link rel="preload" as="image"> for the poster in Base.astro when the hero is above the fold.
  • Responsive sizing — the poster is 1920×1080 but the display area measured 1318×741. Serve a smaller default with srcset/<picture> (e.g. 960/1318/1920 widths), or accept the ~39 KB penalty on desktop. Note the poster doubles as the og:image, so generate both variants from the same source in pnpm run media.
  • Minimize main-thread work — the ~205 ms layout task + inline script at first paint delay the render even after the bytes arrive. Audit the initial inline module (spark canvas init, IntersectionObserver setup, reveal class) for anything that can yield or move behind requestIdleCallback.
  • Improve caching — static assets are content-hashed only in name (they aren't — hero-poster.webp has no hash). Add a website/site/public/_headers file (Cloudflare Pages syntax works with Workers static assets) mapping /media/* to a long max-age + immutable, or hash filenames. Careful: hero.mp4 changes with each hero re-render, so prefer _headers with a bounded max-age (e.g. 1 week) over immutable unless filenames get hashed.
<!-- Example: adding fetchpriority to a video poster -->
<video poster="/media/hero-poster.webp" fetchpriority="high">
  <!-- ... -->
</video>

Note: findings above were identified on a live page in DevTools. Adapt to the stack (Astro components in website/site/src/components/FilmScreen.astro, build pipeline in website/hero-animation/) rather than applying literal CSS overrides.

Acceptance
  • Poster fetch reports High priority in DevTools network
  • Poster transfer ≤ 1318×741-equivalent size on that viewport (or documented decision to keep 1080p for large screens)
  • _headers serving /media/* with Cache-Control: public, max-age≥604800 (verified with curl -sI https://ema.tnsor.network/media/hero-poster.webp | grep -i cache)
  • LCP re-measured with the same methodology; target < 300 ms
Linguagem predominante
TypeScript
Estrelas
829
Forks
234
Merge médio
22h 43min
PRs com merge (30d)
52

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