correctness/autoplay-muted · Autoplay video without muted

Browsers block autoplay with audio, and a blocked autoplay does not error, so a <video autoplay> without muted silently never starts playing for real visitors.

Severity: warning · Category: correctness

What it checks

Flags a <video> element that carries a literal autoplay attribute but no muted attribute:

<video autoplay src="/hero.mp4"></video>

autoplay is an HTML boolean attribute, so its presence is what autoplays and any literal value counts (autoplay="false" still autoplays). An expression-valued autoplay={expr} is unknowable statically and is not flagged. muted in any form passes: a bare muted, muted={expr} (the expression could be true), bind:muted, or a spread attribute that could supply it.

Why it matters

Chrome and Safari block autoplay with audio: autoplay is only honoured when the video is muted or the site has earned an autoplay allowance. A blocked autoplay does not throw. The video just never starts.

One documented exception: both browsers may allow unmuted autoplay for a video that has no audio track at all. A silent hero video without muted can therefore work. The finding is still worth acting on, since muted is harmless there and makes the intent explicit, but it is advisory in that case rather than a guaranteed failure.

This makes the defect invisible in development: after interacting with the page, autoplay is often allowed for the session, so the author sees the video play and ships it. Real visitors get a frozen poster frame. The markup looks correct, compiles, and silently does nothing, which is exactly the class of defect static analysis is for.

How to fix

Add muted, and typically playsinline so iOS plays the video inline instead of refusing or going fullscreen:

<video autoplay muted playsinline src="/hero.mp4"></video>

If the video genuinely needs sound, drop autoplay and start playback from a user gesture instead.

Limitations

Only native <video> elements with a literal autoplay are covered. An expression-valued autoplay is unknowable and is not flagged, and a dynamic tag via <svelte:element this="video"> is not inspected, the same RegularElement-only convention as correctness/checkable-bind-value. <audio autoplay> is out of scope: a muted audio autoplay is meaningless, so the rule’s recommendation does not transfer. An audible <audio autoplay> is blocked the same way but needs a different fix: start playback from a user gesture. muted={expr} passes without evaluating the expression, so a hardcoded muted={false} is not flagged.

Mode differences

None. This rule reads source, the same .svelte and .ts files, everywhere it runs. The CLI, the Vite plugin’s build pass, and the live dashboard’s static baseline all report it identically, and the rendered-HTML pass never re-evaluates it. Scoping a run with --route skips it: component-scoped rules have no route to attribute a finding to.

Disabling

export default {
  rules: {
    'correctness/autoplay-muted': 'off'
  }
};