> ## Documentation Index
> Fetch the complete documentation index at: https://hyperframes-fix-nested-composition-media-inpoint.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Weight Shift

> Elegant font-weight transition between caption lines

export const InstallCommand = ({command, item}) => {
  const [copied, setCopied] = React.useState(false);
  const [tuned, setTuned] = React.useState("");
  React.useEffect(() => {
    if (!item) return;
    const read = () => {
      try {
        const raw = new URLSearchParams(window.location.search).get(`vars-${item}`);
        if (!raw) return setTuned("");
        const parsed = JSON.parse(raw);
        if (!parsed || typeof parsed !== "object" || Array.isArray(parsed)) return setTuned("");
        if (Object.keys(parsed).length === 0) return setTuned("");
        setTuned(` --vars '${JSON.stringify(parsed)}'`);
      } catch {
        setTuned("");
      }
    };
    read();
    window.addEventListener("hf-vars-changed", read);
    window.addEventListener("popstate", read);
    return () => {
      window.removeEventListener("hf-vars-changed", read);
      window.removeEventListener("popstate", read);
    };
  }, [item]);
  const fullCommand = `${command}${tuned}`;
  const copy = async () => {
    try {
      if (navigator.clipboard && window.isSecureContext) {
        await navigator.clipboard.writeText(fullCommand);
      } else {
        const previous = document.activeElement;
        const scratch = document.createElement("textarea");
        scratch.value = fullCommand;
        scratch.setAttribute("readonly", "");
        scratch.style.position = "fixed";
        scratch.style.opacity = "0";
        document.body.appendChild(scratch);
        scratch.select();
        document.execCommand("copy");
        document.body.removeChild(scratch);
        previous?.focus?.();
      }
      setCopied(true);
      setTimeout(() => setCopied(false), 2000);
    } catch {}
  };
  return <div className="hf-install-command not-prose my-4 flex items-stretch overflow-hidden rounded-xl border border-zinc-200 bg-zinc-50 dark:border-zinc-800 dark:bg-zinc-900">
      <code className="flex-1 overflow-x-auto whitespace-nowrap border-r border-zinc-200 px-4 py-3 font-mono text-sm text-zinc-800 dark:border-zinc-800 dark:text-zinc-100">
        {fullCommand}
      </code>
      <button type="button" onClick={copy} data-copied={copied ? "true" : "false"} aria-label={`Copy ${command} to the clipboard`} className="hf-install-copy">
        <svg className="hf-install-copy-clipboard" xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 18 18" fill="none" stroke="currentColor" strokeWidth="1.5" strokeLinecap="round" strokeLinejoin="round" aria-hidden="true">
          <path d="M14.25 5.25H7.25C6.14543 5.25 5.25 6.14543 5.25 7.25V14.25C5.25 15.3546 6.14543 16.25 7.25 16.25H14.25C15.3546 16.25 16.25 15.3546 16.25 14.25V7.25C16.25 6.14543 15.3546 5.25 14.25 5.25Z" />
          <path d="M2.80103 11.998L1.77203 5.07397C1.61003 3.98097 2.36403 2.96397 3.45603 2.80197L10.38 1.77297C11.313 1.63397 12.19 2.16297 12.528 3.00097" />
        </svg>
        <svg className="hf-install-copy-check" xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 18 18" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round" aria-hidden="true">
          <path d="M2.75 9.5L6.5 13.25L15.25 4.5" />
        </svg>
      </button>
      <span className="hf-install-copy-status" role="status" aria-live="polite">
        {copied ? "Copied" : ""}
      </span>
    </div>;
};

<iframe className="w-full aspect-video rounded-xl border-0 bg-zinc-100 dark:bg-zinc-800" title="caption-weight-shift preview" loading="lazy" srcDoc={`<!doctype html><html><head><meta charset="utf-8"><style>html,body{margin:0;height:100%;overflow:hidden;background:transparent}hyperframes-player{display:block;width:100%;height:100%}</style><script src="https://cdn.jsdelivr.net/npm/@hyperframes/player@0.7/dist/hyperframes-player.global.js"><\/script></head><body><script>fetch("/public/catalog/components/caption-weight-shift.json").then(function(r){return r.json()}).then(function(d){var p=document.createElement("hyperframes-player");p.setAttribute("srcdoc",d.html);p.setAttribute("controls","");p.setAttribute("autoplay","");p.setAttribute("loop","");p.setAttribute("muted","");p.setAttribute("poster","https://static.heygen.ai/hyperframes-oss/docs/images/catalog/components/caption-weight-shift.png");document.body.appendChild(p)});<\/script></body></html>`} />

## Install

<InstallCommand command="npx hyperframes add caption-weight-shift" item="caption-weight-shift" />

That writes one file: `compositions/components/caption-weight-shift.html`.

## Source

<Accordion title={`caption-weight-shift.html`}>
  ```html theme={null}
  <!doctype html>
  <html lang="en">
    <head>
      <meta charset="UTF-8" />
      <meta name="viewport" content="width=1920, height=1080" />
      <title>Weight Shift</title>
      <link rel="preconnect" href="https://fonts.googleapis.com" />
      <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
      <link
        href="https://fonts.googleapis.com/css2?family=Montserrat:wght@300;700&display=swap"
        rel="stylesheet"
      />
      <script src="https://cdn.jsdelivr.net/npm/gsap@3.14.2/dist/gsap.min.js"></script>
      <style>
        *,
        *::before,
        *::after {
          box-sizing: border-box;
        }

        html,
        body {
          width: 1920px;
          height: 1080px;
          margin: 0;
          overflow: hidden;
          background: transparent;
          font-family: "Montserrat", Arial, sans-serif;
        }

        #weight-shift {
          pointer-events: none;
          position: relative;
          width: 1920px;
          height: 1080px;
          overflow: hidden;
          background: transparent;
        }

        .caption-layer {
          position: absolute;
          inset: 0;
          z-index: 20;
          pointer-events: none;
          transform: translateZ(0);
        }

        .safe-zone {
          position: absolute;
          bottom: 100px;
          left: 50%;
          transform: translateX(-50%);
          width: 1400px;
          height: 278px;
          display: flex;
          align-items: center;
          justify-content: center;
        }

        .caption-group {
          position: absolute;
          left: 0;
          top: 0;
          width: 1400px;
          height: 278px;
          display: flex;
          align-items: center;
          justify-content: center;
          opacity: 0;
          transform-origin: 50% 50%;
          will-change: transform;
          backface-visibility: hidden;
        }

        .caption-copy {
          display: flex;
          flex-direction: column;
          align-items: center;
          justify-content: center;
          max-width: 1400px;
          text-align: center;
        }

        .caption-line {
          display: flex;
          align-items: center;
          justify-content: center;
          gap: 12px;
          width: max-content;
          max-width: 1400px;
          line-height: 1.1;
          white-space: nowrap;
          color: #ffffff;
          font-family: "Montserrat", Arial, sans-serif;
          font-weight: 300;
          font-size: 72px;
          letter-spacing: -0.03em;
          text-shadow: 0 2px 4px rgba(0, 0, 0, 0.3);
          text-transform: lowercase;
        }
      </style>
    </head>
    <body>
      <div
        id="weight-shift"
        data-composition-id="caption-weight-shift"
        data-timeline-locked
        data-start="0"
        data-duration="8"
        data-fps="30"
        data-width="1920"
        data-height="1080"
      >
        <div class="caption-layer" aria-hidden="true">
          <div id="caption-stage" class="safe-zone"></div>
        </div>
      </div>

      <script>
        var DURATION = 8;
        var SAFE_ZONE_WIDTH = 1400;
        var MAX_LINE_WIDTH = SAFE_ZONE_WIDTH - 40;
        var CAPTION_FONT_SIZE = 72;
        var MAX_WORDS_PER_GROUP = 4;
        var WORD_SPACING = 12;
        var PAUSE_THRESHOLD = 0.1;
        var ENTRY_DURATION = 100 / 1000;
        var WEIGHT_TRANSITION = 100 / 1000;
        var FONT_WIDTH_SAFETY = 1.14;
        var FONT_WEIGHT_LIGHT = 300;
        var FONT_WEIGHT_BOLD = 700;

        var TRANSCRIPT = [
          { text: "Every", start: 0.0, end: 0.3 },
          { text: "great", start: 0.3, end: 0.55 },
          { text: "video", start: 0.55, end: 0.85 },
          { text: "starts", start: 0.85, end: 1.1 },
          { text: "with", start: 1.1, end: 1.25 },
          { text: "a", start: 1.25, end: 1.35 },
          { text: "single", start: 1.35, end: 1.65 },
          { text: "frame.", start: 1.65, end: 2.0 },
          { text: "HyperFrames", start: 2.1, end: 2.65 },
          { text: "lets", start: 2.65, end: 2.85 },
          { text: "you", start: 2.85, end: 2.95 },
          { text: "write", start: 2.95, end: 3.15 },
          { text: "HTML", start: 3.15, end: 3.55 },
          { text: "and", start: 3.55, end: 3.65 },
          { text: "render", start: 3.65, end: 3.95 },
          { text: "professional", start: 3.95, end: 4.45 },
          { text: "video.", start: 4.45, end: 4.8 },
          { text: "No", start: 4.9, end: 5.05 },
          { text: "timeline.", start: 5.05, end: 5.45 },
          { text: "No", start: 5.5, end: 5.65 },
          { text: "drag", start: 5.65, end: 5.85 },
          { text: "and", start: 5.85, end: 5.95 },
          { text: "drop.", start: 5.95, end: 6.25 },
          { text: "Just", start: 6.35, end: 6.55 },
          { text: "code", start: 6.55, end: 6.8 },
          { text: "that", start: 6.8, end: 6.95 },
          { text: "becomes", start: 6.95, end: 7.3 },
          { text: "cinema.", start: 7.3, end: 7.7 },
        ];

        function normalizeWords(rawWords) {
          return rawWords
            .map(function (item) {
              return {
                text: String(item.word || item.text || "").trim(),
                start: Math.max(0, Number(item.start) || 0),
                end: Math.min(DURATION, Math.max(Number(item.start) || 0, Number(item.end) || 0)),
              };
            })
            .filter(function (word) {
              return word.text.length > 0;
            });
        }

        var _fitCanvas = document.createElement("canvas");
        var _fitCtx = _fitCanvas.getContext("2d");
        function fitFontSize(text, baseFontSize, fontWeight, fontFamily, maxWidth) {
          var size = baseFontSize;
          var minSize = Math.floor(baseFontSize * 0.45);
          while (size > minSize) {
            _fitCtx.font = fontWeight + " " + size + "px " + fontFamily;
            if (_fitCtx.measureText(text).width <= maxWidth) return size;
            size -= 2;
          }
          return minSize;
        }

        var measureCanvas = document.createElement("canvas");
        var measureContext = measureCanvas.getContext("2d");
        measureContext.font = "700 " + CAPTION_FONT_SIZE + "px Montserrat";

        function measureWord(word) {
          return measureContext.measureText(word.text.toLowerCase()).width * FONT_WIDTH_SAFETY;
        }

        function measureLineWidth(words) {
          return words.reduce(function (total, word, index) {
            return total + measureWord(word) + (index ? WORD_SPACING : 0);
          }, 0);
        }

        function fitsInTwoLines(words) {
          return measureLineWidth(words) <= MAX_LINE_WIDTH * 1.8;
        }

        function splitLines(words) {
          if (words.length < 2) {
            return [{ words: words, startIndex: 0 }];
          }
          var bestSplit = Math.ceil(words.length / 2);
          var bestDiff = Infinity;
          for (var s = 1; s < words.length; s++) {
            var w1 = measureLineWidth(words.slice(0, s));
            var w2 = measureLineWidth(words.slice(s));
            if (w1 <= MAX_LINE_WIDTH && w2 <= MAX_LINE_WIDTH) {
              var diff = Math.abs(w1 - w2);
              if (diff < bestDiff) {
                bestDiff = diff;
                bestSplit = s;
              }
            }
          }
          var result = [];
          var line1 = words.slice(0, bestSplit);
          var line2 = words.slice(bestSplit);
          if (line1.length) result.push({ words: line1, startIndex: 0 });
          if (line2.length) result.push({ words: line2, startIndex: line1.length });
          return result;
        }

        function avoidSingleWordGroups(groups) {
          var out = [];
          groups.forEach(function (group) {
            if (
              group.words.length === 1 &&
              out.length > 0 &&
              out[out.length - 1].words.length < MAX_WORDS_PER_GROUP
            ) {
              out[out.length - 1] = makeGroup(out[out.length - 1].words.concat(group.words));
            } else {
              out.push(group);
            }
          });

          for (var i = 0; i < out.length; i++) {
            if (out[i].words.length !== 1) continue;
            if (i + 1 < out.length && out[i + 1].words.length < MAX_WORDS_PER_GROUP) {
              out[i] = makeGroup(out[i].words.concat(out[i + 1].words));
              out.splice(i + 1, 1);
            } else if (i > 0 && out[i - 1].words.length < MAX_WORDS_PER_GROUP) {
              out[i - 1] = makeGroup(out[i - 1].words.concat(out[i].words));
              out.splice(i, 1);
              i--;
            }
          }

          return out;
        }

        function makeGroups(words) {
          var groups = [];
          var current = [];
          words.forEach(function (word, index) {
            var nextWord = words[index + 1];
            var testGroup = current.concat([word]);
            if (testGroup.length > MAX_WORDS_PER_GROUP || !fitsInTwoLines(testGroup)) {
              if (current.length) groups.push(makeGroup(current));
              current = [word];
              return;
            }
            current.push(word);
            var punctuation = /[,.:!?]$/.test(word.text);
            var pause = nextWord ? nextWord.start - word.end : 0;
            if (
              !nextWord ||
              punctuation ||
              pause >= PAUSE_THRESHOLD ||
              current.length >= MAX_WORDS_PER_GROUP
            ) {
              groups.push(makeGroup(current));
              current = [];
            }
          });
          if (current.length) groups.push(makeGroup(current));
          return avoidSingleWordGroups(groups);
        }

        function makeGroup(words) {
          return {
            words: words.slice(),
            lines: splitLines(words),
            start: words[0].start,
            end: words[words.length - 1].end,
          };
        }

        function buildCaptions(groups) {
          var stage = document.getElementById("caption-stage");
          groups.forEach(function (group, groupIndex) {
            var groupText = group.words
              .map(function (w) {
                return w.text.toLowerCase();
              })
              .join(" ");
            var computedSize = fitFontSize(
              groupText,
              CAPTION_FONT_SIZE,
              "700",
              "Montserrat",
              MAX_LINE_WIDTH,
            );
            var groupEl = document.createElement("div");
            var copyEl = document.createElement("div");
            groupEl.id = "caption-group-" + groupIndex;
            groupEl.className = "caption-group";
            copyEl.className = "caption-copy";
            group.lines.forEach(function (line, lineIndex) {
              var lineEl = document.createElement("div");
              lineEl.className = "caption-line";
              lineEl.id = "caption-group-" + groupIndex + "-line-" + lineIndex;
              lineEl.style.fontWeight = lineIndex === 0 ? FONT_WEIGHT_BOLD : FONT_WEIGHT_LIGHT;
              lineEl.style.fontSize = computedSize + "px";
              line.words.forEach(function (word, wordIndex) {
                var wordEl = document.createElement("span");
                wordEl.textContent = word.text.toLowerCase();
                wordEl.style.display = "inline-block";
                lineEl.appendChild(wordEl);
              });
              copyEl.appendChild(lineEl);
            });
            groupEl.appendChild(copyEl);
            stage.appendChild(groupEl);
          });
        }

        var WORDS = normalizeWords(TRANSCRIPT);
        var GROUPS = makeGroups(WORDS);
        buildCaptions(GROUPS);

        window.__timelines = window.__timelines || {};
        var tl = gsap.timeline({ paused: true });

        var visibleStarts = GROUPS.map(function (group, groupIndex) {
          var prev = GROUPS[groupIndex - 1];
          var availableGap = prev ? Math.max(0, group.start - prev.end) : ENTRY_DURATION;
          var entryLead = Math.min(ENTRY_DURATION, availableGap);
          return Math.max(0, group.start - entryLead);
        });

        var allGroupEls = GROUPS.map(function (_, i) {
          return document.getElementById("caption-group-" + i);
        });

        GROUPS.forEach(function (group, groupIndex) {
          var groupEl = allGroupEls[groupIndex];
          var visibleStart = visibleStarts[groupIndex];
          var visibleEnd = groupIndex < GROUPS.length - 1 ? visibleStarts[groupIndex + 1] : DURATION;

          allGroupEls.forEach(function (otherEl, otherIndex) {
            if (otherIndex !== groupIndex) tl.set(otherEl, { opacity: 0 }, visibleStart);
          });

          tl.set(groupEl, { opacity: 0, scale: 0.85 }, visibleStart);
          tl.to(
            groupEl,
            { opacity: 1, scale: 1, duration: ENTRY_DURATION, ease: "power3.out", force3D: true },
            visibleStart,
          );

          if (group.lines.length === 2) {
            var line1El = document.getElementById("caption-group-" + groupIndex + "-line-0");
            var line2El = document.getElementById("caption-group-" + groupIndex + "-line-1");
            var line2FirstWord = group.lines[1].words[0];
            var switchTime = line2FirstWord.start;

            tl.to(
              line1El,
              { fontWeight: FONT_WEIGHT_LIGHT, duration: WEIGHT_TRANSITION, ease: "power2.out" },
              switchTime,
            );
            tl.to(
              line2El,
              { fontWeight: FONT_WEIGHT_BOLD, duration: WEIGHT_TRANSITION, ease: "power2.out" },
              switchTime,
            );
          }

          tl.set(groupEl, { opacity: 0 }, visibleEnd);
        });

        window.__timelines["caption-weight-shift"] = tl;
      </script>
    </body>
  </html>
  ```
</Accordion>

## Usage

Open `compositions/components/caption-weight-shift.html` and paste its contents into your composition. See the comment header in the file for detailed instructions.

Tagged `captions` `caption-style` `minimal` `typography`.

## Related topics

* [Browse the complete Catalog](/catalog)
* [Add assets and Catalog items in Studio](/studio/assets-and-blocks)
* [Build a richer composition](/go-further)
