feat(spf): Added autoplay support

[spuppo-mux]

Summary

autoplay had no effect on the SPF HLS adapter unless preload was also set.

Root cause: the adapter never bridged autoplay to the engine's load activation. With preload unset or none, the engine loads nothing until loadActivated flips true — but loadActivated only flips on a DOM play/seeking event, and nothing plays until data has loaded. Setting preload sidestepped it by loading independently, which is why autoplay only "worked" alongside a preload value.

Part of #1795 (media API extensions on the SPF adapter).

Fix

trackLoadTriggers now treats el.autoplay as an upfront commitment to load, alongside the existing "already playing / mid-seek on entry" checks. When the attached media element has autoplay on entry to monitoring, loadActivated is set to true immediately (no play / seeking listeners attached) rather than waiting for a play event that preload="none" would never let fire.

if (el.autoplay || !el.paused || el.seeking) {
  setLoadActivated();
  return;
}

The browser's autoplay policy (muted-gating, unmuted blocking) is untouched. SPF just gets far enough for the browser to make its own call.

Autoplay is read straight off context.mediaElement, with no state slot and no adapter/engine changes. The element is already the source of truth: <simple-hls-video autoplay> reflects the attribute onto the inner <video> (via CustomMediaElement), and the low-level engine harness sets video.autoplay directly before attach.

Repro

Go to Sandbox on /?platform=html&styling=css&preset=simple-hls-video&skin=default&source=hls-multi-audio&autoplay=1&muted=1&loop=0&preload=none&locale=en (simple-hls muted autoplay, no preload) and validate that before the changes this does not autoplay but after this changes it does.

Example: On another branch, this does not autoplay even though autoplay is on https://v10-sandbox-git-fork-spuppo-mux-feat-spf-adapter-med-3b75be-mux.vercel.app/?platform=html&styling=css&preset=simple-hls-video&skin=default&source=hls-multi-audio&autoplay=1&muted=1&loop=0&preload=none&locale=en

Go to the same path on this deployment and it should work.
https://v10-sandbox-kvd3wy019-mux.vercel.app/?platform=html&styling=css&preset=simple-hls-video&skin=default&source=hls-multi-audio&autoplay=1&muted=1&loop=0&preload=none&locale=en

Same for https://v10-sandbox-kvd3wy019-mux.vercel.app/spf-segment-loading/?muted=true&autoplay=true&preload=none

Some other cases:

• autoplay + muted -> autoplay starts normally
• autoplay + not muted -> autoplay doesn't start (unless hot reloading the page and you had already interacted with video); however will fetch 5 segments for both cases
• no autoplay -> wont start, respects preload (except for the found bug in adapter, see Notes)

Testing

• trackLoadTriggers: new case asserting autoplay on entry sets loadActivated=true and attaches no play/seeking listeners; autoplay added to the fake-video helper.
• pnpm typecheck and pnpm -F @videojs/spf test (1044 passing) — green; Biome clean on changed files.

Notes

• While testing noticed there is a bug with the sync-preload behavior and our Sandbox example. Essentially even if preload is set to none, it will always start as metadata. This is because sync-preload expects to read the preload attribute from the video element which never is never reached by our example. We should change either the behavior or the adapter.
• Autoplay read off the element with no backing signal → reactivity scoped to element identity (toggling autoplay on the same attached element post-monitoring isn't picked up; fine for autoplay semantics).
• No adapter/engine/sync-preload changes — earlier engine-slot and preload-folding iterations were reverted.

---

Note

Medium Risk
Changes when segment loading starts via loadActivated, which gates HLS load behavior, but the scope is narrow and covered by new unit tests.

Overview
trackLoadTriggers now treats el.autoplay like an upfront commitment to load, not only play / seeking or an already-playing element. When the attached media element has autoplay on entry, loadActivated is set to true immediately and play / seeking listeners are not attached, so preload="none" no longer blocks loading while waiting for a play event that never comes.

Tests add autoplay to the fake video helper and assert the new on-entry activation path and that listeners stay detached.

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[cjpillsbury]

LGTM! Ship it.

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[cjpillsbury]

I'm down. We may want to revisit this, but this also may be good enough for now (and maybe even the "right" solution overall).