DominiqueKarreman

/* Deliberately NOT guarded by a boolean "seeking" flag. A seek issued
   before the video has data never fires `seeked`, and a flag set on the
   way in then never clears -- one dropped event and the scrubber is dead
   for the rest of the session. Trust the browser's own video.seeking and
   re-check next frame, so a dropped seek simply gets reissued. */
function syncSeek() {
  if (!duration) return;
  const t = smooth * duration;
  if (Math.abs(t - video.currentTime) <= 1 / 48) { stalled = 0; return; }

  if (!video.seeking) {
    if (video.currentTime === lastAt && ++stalled > 90) return;
    lastAt = video.currentTime;
    video.currentTime = t;
  }
  if (!seekRaf) seekRaf = requestAnimationFrame(() => { seekRaf = 0; syncSeek(); });
}

/* threshold MUST stay 0. The resting state clips the element to zero
   height, and IntersectionObserver measures ratio after clipping -- so
   any non-zero threshold can never be met and the reveal never fires.
   isIntersecting is still true, so set the trigger with rootMargin. */
const io = new IntersectionObserver((entries) => {
  for (const e of entries) {
    if (!e.isIntersecting) continue;
    e.target.classList.add('is-in');
    io.unobserve(e.target);          // an entrance replayed is noise
  }
}, { threshold: 0, rootMargin: '0px 0px -14% 0px' });