// Uses an existing, authorized media element; does not export a changed file.
async function observeTeachingPlaybackRate(media, rate, milliseconds = 450) {
  if (![1, 1.25].includes(rate)) throw new Error('this exercise allows only 1 or 1.25');
  if (!(Number.isFinite(media.duration) && media.duration > 1.5))
    throw new Error('loaded teaching media longer than 1.5 seconds required');
  media.pause(); media.currentTime = 0;
  if (media.seeking) await new Promise(resolve => media.addEventListener('seeked', resolve, {once:true}));
  media.playbackRate = rate;
  const pitchPropertyExists = 'preservesPitch' in media;
  if (pitchPropertyExists) media.preservesPitch = true;
  await media.play();
  const start = media.currentTime, wallStart = performance.now();
  await new Promise(resolve => setTimeout(resolve, milliseconds));
  media.pause();
  return {requestedRate:rate, acceptedRate:media.playbackRate,
    duration:media.duration, mediaSecondsAdvanced:media.currentTime-start,
    wallSecondsObserved:(performance.now()-wallStart)/1000,
    pitchPropertyExists, preservesPitch: pitchPropertyExists ? media.preservesPitch : null,
    pitchQualityListened:false, TTSGenerated:false, changedFileExported:false};
}