ナレーションが途切れず、音声解説が入りきらない動画

<video id="brew-video" controls preload="metadata"  src="brew-talk.webm" poster="brew-talk.jpg"−  data-described="brew-talk.described.webm">  <track kind="captions" srclang="ja" label="日本語"−    src="brew-talk.ja.vtt" data-described="brew-talk.described.ja.vtt"></video><button type="button" id="describe" aria-pressed="false">  音声解説</button> <script>  const video = document.getElementById('brew-video');  const track = video.querySelector('track');  const plain = { video: video.getAttribute('src'), captions: track.getAttribute('src') };  document.getElementById('describe').addEventListener('click', (event) => {    const button = event.currentTarget;    const on = button.getAttribute('aria-pressed') !== 'true';    const { currentTime, paused, playbackRate } = video;    const captions = track.track.mode;    video.src = on ? video.dataset.described : plain.video;    track.src = on ? track.dataset.described : plain.captions;    // 同じ位置、同じ速度で、字幕も元の表示のまま続ける。    video.addEventListener('loadedmetadata', () => {−      video.currentTime = currentTime;      video.playbackRate = playbackRate;      track.track.mode = captions;      if (!paused) video.play();    }, { once: true });    button.setAttribute('aria-pressed', String(on));  });</script>

<video id="brew-video" controls preload="metadata"  src="brew-talk.webm" poster="brew-talk.jpg"+  data-described="brew-talk.extended.webm"+  data-holds="[[15.22, 2.54], [21.06, 3.82]]">  <track kind="captions" srclang="ja" label="日本語"+    src="brew-talk.ja.vtt" data-described="brew-talk.extended.ja.vtt"></video><button type="button" id="describe" aria-pressed="false">  音声解説</button> <script>  const video = document.getElementById('brew-video');  const track = video.querySelector('track');  const plain = { video: video.getAttribute('src'), captions: track.getAttribute('src') };  // 拡張版が映像を止める位置：元の動画での時刻と、止める秒数。+  const holds = JSON.parse(video.dataset.holds);+  const toExtended = (time) => time + holds+    .filter(([at]) => at < time)+    .reduce((sum, [, held]) => sum + held, 0);+  const toOriginal = (time) => {+    let shift = 0;+    for (const [at, held] of holds) {+      if (time < at + shift) break;      // 止めている途中なら、止め始めた位置に戻す。+      shift += Math.min(held, time - at - shift);+    }+    return time - shift;+  };  document.getElementById('describe').addEventListener('click', (event) => {    const button = event.currentTarget;    const on = button.getAttribute('aria-pressed') !== 'true';    const { currentTime, paused, playbackRate } = video;    const captions = track.track.mode;    video.src = on ? video.dataset.described : plain.video;    track.src = on ? track.dataset.described : plain.captions;    // 同じ位置、同じ速度で、字幕も元の表示のまま続ける。    video.addEventListener('loadedmetadata', () => {+      video.currentTime = on ? toExtended(currentTime) : toOriginal(currentTime);      video.playbackRate = playbackRate;      track.track.mode = captions;      if (!paused) video.play();    }, { once: true });    button.setAttribute('aria-pressed', String(on));  });</script>