@@ -96,6 +96,41 @@ describe("inert region scanning", () => {
 });
 
 describe("opening tag scanning", () => {
+  it.each([injectDurations, clampDurations])(
+    "keeps long unclosed ID-targeted tags unchanged in %p",
+    (write) => {
+      const html = '<video id="target" '.repeat(100_000);
+      expect(write(html, [{ id: "target", duration: 3 }])).toBe(html);
+    },
+  );
+
+  it.each(["target", "a>b", "a<b", "a.b[0]"])(
+    "preserves substring-ID matches and delimiter characters for %j",
+    (id) => {
+      const html = `<video data-id="${id}" data-start="1" data-duration="bad" data-end="4">`;
+      expect(injectDurations(html, [{ id, duration: 3 }])).toBe(
+        `<video data-id="${id}" data-start="1" data-duration="3" data-end="4">`,
+      );
+      expect(clampDurations(html, [{ id, duration: 3 }])).toBe(
+        `<video data-id="${id}" data-start="1" data-duration="3" data-end="4">`,
+      );
+    },
+  );
+
+  it("leaves similar IDs alone and applies repeated resolutions in order", () => {
+    const html = '<video id="a.b" data-start="1" data-duration="bad"><video id="axb">';
+    const resolutions = [
+      { id: "a.b", duration: 3 },
+      { id: "a.b", duration: 5 },
+    ];
+    expect(injectDurations(html, resolutions)).toBe(
+      '<video id="a.b" data-start="1" data-duration="3" data-end="4"><video id="axb">',
+    );
+    expect(clampDurations(html, resolutions)).toBe(
+      '<video id="a.b" data-start="1" data-duration="5"><video id="axb">',
+    );
+  });
+
   it.each(["<video", "<audio", "<div", "<section", "<video<audio<div<section"])(
     "preserves an unclosed %j suffix after compiling complete media",
     (prefix) => {
 
@@ -181,6 +181,33 @@ function replaceOpeningTags(
   return parts.join("");
 }
 
+function replaceIdTags(html: string, id: string, replace: (tag: string) => string): string {
+  const idPattern = new RegExp(`id=["']${escapeRegex(id)}["']`, "gi");
+  const lastClosing = html.lastIndexOf(">");
+  const parts: string[] = [];
+  let cursor = 0;
+  let candidate = idPattern.exec(html);
+  for (const { index, end } of iterateOpeningTags(html, /</g)) {
+    if (index < cursor) continue;
+    let targetEnd = -1;
+    while (candidate && candidate.index < end) {
+      const candidateEnd = candidate.index + candidate[0].length;
+      if (candidate.index > index && candidateEnd <= lastClosing) targetEnd = candidateEnd;
+      // Preserve the old greedy prefix's last matching ID, including overlaps.
+      idPattern.lastIndex = candidate.index + 1;
+      candidate = idPattern.exec(html);
+    }
+    if (targetEnd < 0) continue;
+    // An authored ID can itself contain '>', so its closer may follow the
+    // initial span. The lastClosing check guarantees a closing delimiter.
+    const closing = html.indexOf(">", targetEnd) + 1;
+    parts.push(html.slice(cursor, index), replace(html.slice(index, closing)));
+    cursor = closing;
+  }
+  parts.push(html.slice(cursor));
+  return parts.join("");
+}
+
 function compileTag(
   tag: string,
   isVideo: boolean,
@@ -302,9 +329,7 @@ export function compileTimingAttrs(html: string): CompilationResult {
 export function injectDurations(html: string, resolutions: ResolvedDuration[]): string {
   for (const { id, duration } of resolutions) {
     // Match the element's opening tag by id
-    const idPattern = new RegExp(`(<[^>]*id=["']${escapeRegex(id)}["'][^>]*>)`, "gi");
-
-    html = html.replace(idPattern, (tag) => {
+    html = replaceIdTags(html, id, (tag) => {
       let result = tag;
 
       // Add data-duration if missing
@@ -373,9 +398,7 @@ export function extractResolvedMedia(html: string): ResolvedMediaElement[] {
  */
 export function clampDurations(html: string, clamps: ResolvedDuration[]): string {
   for (const { id, duration } of clamps) {
-    const idPattern = new RegExp(`(<[^>]*id=["']${escapeRegex(id)}["'][^>]*>)`, "gi");
-
-    html = html.replace(idPattern, (tag) => {
+    html = replaceIdTags(html, id, (tag) => {
       // Replace data-duration value
       tag = tag.replace(/data-duration=["'][^"']*["']/, `data-duration="${duration}"`);