diff --git a/packages/core/src/compiler/timingCompiler.test.ts b/packages/core/src/compiler/timingCompiler.test.ts
index a3f411f8e0..42f6f8b789 100644
--- a/packages/core/src/compiler/timingCompiler.test.ts
+++ b/packages/core/src/compiler/timingCompiler.test.ts
@@ -116,6 +116,17 @@ describe("compileTimingAttrs", () => {
     expect(compiled).not.toContain("data-hf-auto-start");
   });
 
+  it("leaves data-end off a relative data-start id-ref", () => {
+    const html =
+      '<video id="intro" src="a.mp4" data-start="0" data-duration="10">' +
+      '<video id="main" src="b.mp4" data-start="intro" data-duration="20">';
+    const { html: compiled } = compileTimingAttrs(html);
+
+    expect(compiled).toContain('data-start="intro"');
+    expect(compiled).not.toMatch(/id="main"[^>]*data-end=/);
+    expect(compiled).toMatch(/id="intro"[^>]*data-end="10"/);
+  });
+
   it("compiles audio tags the same as video (minus data-has-audio)", () => {
     const html = '<audio id="a1" src="music.mp3" data-start="0" data-duration="10">';
     const { html: compiled } = compileTimingAttrs(html);
@@ -212,6 +223,15 @@ describe("injectDurations", () => {
     // data-duration already present, should not be duplicated
     expect(result).toContain('data-duration="3"');
   });
+
+  it("injects data-duration but not data-end when data-start is a relative id-ref", () => {
+    const html = '<video id="main" src="b.mp4" data-start="intro">';
+    const result = injectDurations(html, [{ id: "main", duration: 5 }]);
+
+    expect(result).toContain('data-duration="5"');
+    expect(result).toContain('data-start="intro"');
+    expect(result).not.toMatch(/data-end=/);
+  });
 });
 
 describe("extractResolvedMedia", () => {
diff --git a/packages/core/src/compiler/timingCompiler.ts b/packages/core/src/compiler/timingCompiler.ts
index 715634adc6..f121cc4ae7 100644
--- a/packages/core/src/compiler/timingCompiler.ts
+++ b/packages/core/src/compiler/timingCompiler.ts
@@ -2,7 +2,7 @@
  * Timing Compiler
  *
  * Shared, pure HTML compilation that normalizes timing attributes.
- * Works in both Node.js and browser (no dependencies, regex-based).
+ * Works in both Node.js and browser (regex-based, no DOM).
  *
  * Guarantees every timed element gets:
  * - id on media elements when missing
@@ -13,8 +13,13 @@
  * this compiler identifies them as "unresolved" so the caller can provide
  * durations via an environment-specific resolver (ffprobe, el.duration, etc.)
  * and call injectDurations() to complete the compilation.
+ *
+ * Relative `data-start` (`intro`, `intro + 0.5`) is not numeric — leave
+ * `data-end` off so extract can resolve the id-ref later.
  */
 
+import { parseNumeric } from "@hyperframes/parsers/composition-contract";
+
 // ── Types ────────────────────────────────────────────────────────────────
 
 export interface UnresolvedElement {
@@ -136,23 +141,25 @@ function compileTag(
     result = injectAttr(result, "data-hf-auto-start", "");
     startStr = "0";
   }
-  const start = parseFloat(startStr);
+  const start = parseNumeric(startStr);
   const mediaStartStr = getAttr(result, "data-media-start");
-  const mediaStart = mediaStartStr ? parseFloat(mediaStartStr) : 0;
+  const mediaStart = parseNumeric(mediaStartStr) ?? 0;
 
-  // 1. Compute data-end from data-start + data-duration
+  // 1. Compute data-end from data-start + data-duration. Skip relative id-refs.
   if (!hasAttr(result, "data-end")) {
     const durationStr = getAttr(result, "data-duration");
     if (durationStr !== null) {
-      const end = start + parseFloat(durationStr);
-      result = injectAttr(result, "data-end", String(end));
+      if (start != null) {
+        const end = start + parseFloat(durationStr);
+        if (Number.isFinite(end)) result = injectAttr(result, "data-end", String(end));
+      }
     } else if (id) {
       // No data-duration: mark as unresolved so caller can provide it
       unresolved = {
         id,
         tagName: isVideo ? "video" : "audio",
         src: getAttr(result, "src") ?? undefined,
-        start,
+        start: start ?? 0,
         mediaStart,
       };
     }
@@ -213,7 +220,7 @@ export function compileTimingAttrs(html: string): CompilationResult {
       unresolved.push({
         id,
         tagName: "div",
-        start: startStr ? parseFloat(startStr) : 0,
+        start: parseNumeric(startStr) ?? 0,
         mediaStart: 0,
         compositionSrc: compositionSrc ?? undefined,
       });
@@ -245,11 +252,12 @@ export function injectDurations(html: string, resolutions: ResolvedDuration[]):
         result = injectAttr(result, "data-duration", String(duration));
       }
 
-      // Add data-end if missing
+      // Add data-end if missing. Skip relative id-refs.
       if (!hasAttr(result, "data-end")) {
-        const startStr = getAttr(result, "data-start");
-        const start = startStr ? parseFloat(startStr) : 0;
-        result = injectAttr(result, "data-end", String(start + duration));
+        const start = parseNumeric(getAttr(result, "data-start"));
+        if (start != null) {
+          result = injectAttr(result, "data-end", String(start + duration));
+        }
       }
 
       return result;
@@ -290,9 +298,9 @@ export function extractResolvedMedia(html: string): ResolvedMediaElement[] {
       id,
       tagName: isVideo ? "video" : "audio",
       src: getAttr(tag, "src") ?? undefined,
-      start: startStr !== null ? parseFloat(startStr) : 0,
+      start: parseNumeric(startStr) ?? 0,
       duration,
-      mediaStart: mediaStartStr ? parseFloat(mediaStartStr) : 0,
+      mediaStart: parseNumeric(mediaStartStr) ?? 0,
       loop: hasAttr(tag, "loop"),
     });
   }
@@ -313,10 +321,10 @@ export function clampDurations(html: string, clamps: ResolvedDuration[]): string
       // Replace data-duration value
       tag = tag.replace(/data-duration=["'][^"']*["']/, `data-duration="${duration}"`);
 
-      // Recompute data-end from data-start + clamped duration
-      const startStr = getAttr(tag, "data-start");
-      const start = startStr ? parseFloat(startStr) : 0;
-      tag = tag.replace(/data-end=["'][^"']*["']/, `data-end="${start + duration}"`);
+      const start = parseNumeric(getAttr(tag, "data-start"));
+      if (start != null) {
+        tag = tag.replace(/data-end=["'][^"']*["']/, `data-end="${start + duration}"`);
+      }
 
       return tag;
     });
diff --git a/packages/engine/src/index.ts b/packages/engine/src/index.ts
index a10070ce1f..dbcf500ddd 100644
--- a/packages/engine/src/index.ts
+++ b/packages/engine/src/index.ts
@@ -211,6 +211,8 @@ export {
   isVideoFrameFormat,
 } from "./services/videoFrameExtractor.js";
 
+export { resolveReferencedStart, type RefResolverEl } from "./services/referenceResolver.js";
+
 export { createVideoFrameInjector } from "./services/videoFrameInjector.js";
 
 export {
diff --git a/packages/engine/src/services/videoFrameExtractor.test.ts b/packages/engine/src/services/videoFrameExtractor.test.ts
index a5470f14a3..abdbd9aec2 100644
--- a/packages/engine/src/services/videoFrameExtractor.test.ts
+++ b/packages/engine/src/services/videoFrameExtractor.test.ts
@@ -44,6 +44,7 @@ import {
 import { runFfmpeg } from "../utils/runFfmpeg.js";
 import { COMPLETE_SENTINEL, GC_MARKER, SCHEMA_PREFIX } from "./extractionCache.js";
 import { resolveRuntimeMediaClipDuration } from "../../../core/src/runtime/media.js";
+import { compileTimingAttrs } from "@hyperframes/core";
 
 // ffmpeg is not preinstalled on GitHub's ubuntu-24.04 runners. The producer
 // regression test at packages/producer/tests/vfr-screen-recording/ runs inside
@@ -704,6 +705,16 @@ describe("parseVideoElements", () => {
     expect(main?.end).toBe(30);
   });
 
+  it("still resolves relative data-start after compileTimingAttrs", () => {
+    const raw =
+      '<video id="intro" src="a.mp4" data-start="0" data-duration="10"></video>' +
+      '<video id="main" src="b.mp4" data-start="intro" data-duration="20"></video>';
+    const { html } = compileTimingAttrs(raw);
+    const main = parseVideoElements(html).find((v) => v.id === "main");
+    expect(main?.start).toBe(10);
+    expect(main?.end).toBe(30);
+  });
+
   it("applies + and - offsets on a relative reference", () => {
     const videos = parseVideoElements(
       '<video id="intro" src="a.mp4" data-start="0" data-duration="10"></video>' +
diff --git a/packages/producer/src/services/htmlCompiler.test.ts b/packages/producer/src/services/htmlCompiler.test.ts
index e4de83b375..3d7ed44549 100644
--- a/packages/producer/src/services/htmlCompiler.test.ts
+++ b/packages/producer/src/services/htmlCompiler.test.ts
@@ -1029,6 +1029,7 @@ describe("template-wrapped sub-composition media offsets", () => {
     hostAttrs: string,
     mediaAttrs: string = 'data-start="0" data-duration="4"',
     extraMediaMarkup: string = "",
+    extraRootMarkup: string = "",
   ): {
     projectDir: string;
     indexPath: string;
@@ -1050,6 +1051,7 @@ describe("template-wrapped sub-composition media offsets", () => {
       data-height="360"
       data-duration="4"
     >
+      ${extraRootMarkup}
       <div
         id="scene-host"
         data-composition-id="scene"
@@ -1115,6 +1117,21 @@ describe("template-wrapped sub-composition media offsets", () => {
     });
   });
 
+  it("resolves a host data-start id-ref against a sibling clip", async () => {
+    const { projectDir, indexPath } = writeTemplateWrappedProject(
+      'data-start="intro" data-duration="2" data-width="640" data-height="360"',
+      'data-start="0" data-duration="4"',
+      "",
+      '<video id="intro" src="assets/clip.mp4" data-start="0" data-duration="10" muted></video>',
+    );
+
+    const compiled = await compileForRender(projectDir, indexPath, projectDir);
+    expect(compiled.videos.find((v) => v.id === "scene-video")).toMatchObject({
+      start: 10,
+      end: 14,
+    });
+  });
+
   it("preserves first-pass media offsets when durations are resolved after inlining", async () => {
     const { projectDir, indexPath } = writeTemplateWrappedProject(
       'data-start="2" data-width="640" data-height="360"',
diff --git a/packages/producer/src/services/htmlCompiler.ts b/packages/producer/src/services/htmlCompiler.ts
index ff8fe7a0b0..c630b35e21 100644
--- a/packages/producer/src/services/htmlCompiler.ts
+++ b/packages/producer/src/services/htmlCompiler.ts
@@ -54,6 +54,8 @@ import {
   assertMediaPayload,
   NotMediaPayloadError,
   probeMediaProfile,
+  resolveReferencedStart,
+  type RefResolverEl,
 } from "@hyperframes/engine";
 import {
   downloadToTemp,
@@ -630,6 +632,8 @@ async function parseSubCompositions(
 
   const { document } = parseHTML(html);
   const compEls = document.querySelectorAll("[data-composition-src]");
+  const startCache = new Map<RefResolverEl, number>();
+  const visiting = new Set<RefResolverEl>();
 
   // Build work items, filtering out invalid/circular entries synchronously
   const workItems: Array<{
@@ -645,7 +649,7 @@ async function parseSubCompositions(
     const srcPath = el.getAttribute("data-composition-src");
     if (!srcPath) continue;
 
-    const elStart = parseFloat(el.getAttribute("data-start") || "0");
+    const elStart = resolveReferencedStart(document, el, startCache, visiting);
     const elEndRaw = el.getAttribute("data-end");
     const elEnd = elEndRaw ? parseFloat(elEndRaw) : Infinity;