heygen-com · vanceingalls · Jul 11, 2026 · Jul 11, 2026
diff --git a/packages/engine/src/services/frameCapture-verifySampleFractions.test.ts b/packages/engine/src/services/frameCapture-verifySampleFractions.test.ts
@@ -0,0 +1,36 @@
+import { describe, expect, it } from "vitest";
+import { computeDeVerifySampleFractions } from "./frameCapture.js";
+
+describe("computeDeVerifySampleFractions", () => {
+  it("pins the last sample at 95% so late-onset damage is sampled", () => {
+    const fractions = computeDeVerifySampleFractions(4);
+    expect(fractions).toEqual([0.25, 0.5, 0.75, 0.95]);
+  });
+
+  it("keeps the requested sample count", () => {
+    for (const k of [1, 2, 3, 4, 8]) {
+      expect(computeDeVerifySampleFractions(k)).toHaveLength(k);
+    }
+  });
+
+  it("uses only the tail sample when k is 1", () => {
+    expect(computeDeVerifySampleFractions(1)).toEqual([0.95]);
+  });
+
+  it("returns an empty grid when verification is disabled", () => {
+    expect(computeDeVerifySampleFractions(0)).toEqual([]);
+    expect(computeDeVerifySampleFractions(-2)).toEqual([]);
+  });
+
+  it("stays strictly increasing within (0, 1) for every supported k", () => {
+    for (let k = 1; k <= 8; k++) {
+      const fractions = computeDeVerifySampleFractions(k);
+      for (let i = 0; i < fractions.length; i++) {
+        const f = fractions[i] ?? 0;
+        expect(f).toBeGreaterThan(0);
+        expect(f).toBeLessThan(1);
+        if (i > 0) expect(f).toBeGreaterThan(fractions[i - 1] ?? 0);
+      }
+    }
+  });
+});
diff --git a/packages/engine/src/services/frameCapture.ts b/packages/engine/src/services/frameCapture.ts
@@ -3107,6 +3107,19 @@ export async function getCompositionDuration(session: CaptureSession): Promise<n
  * init-time screenshot → the render falls back to the screenshot path (slower,
  * never wrong). Cost when passing: ~K×(seek+screenshot) ≈ 150–300ms at init.
  */
+/**
+ * Timeline fractions the self-verify samples. First k-1 evenly spaced, last
+ * pinned at 95%: late-onset damage (an end-of-comp reveal exposing pixels DE
+ * paints wrong) was invisible to the old (i+1)/(k+1) grid, whose final sample
+ * sat at 80% — measured miss: a body-gradient drop starting at ~79% of the
+ * timeline passed verification while the drained output bottomed at 30.9 dB.
+ */
+export function computeDeVerifySampleFractions(k: number): number[] {
+  if (k <= 0) return [];
+  if (k === 1) return [0.95];
+  return [...Array.from({ length: k - 1 }, (_, i) => (i + 1) / k), 0.95];
+}
+
 async function captureDeVerificationFrames(
   session: CaptureSession,
   page: Page,
@@ -3153,7 +3166,7 @@ async function captureDeVerificationFrames(
   // render (the detectCssEffectRisk lesson), and because DE frames and truth
   // would share the corruption, PSNR would pass on the damaged output.
   // Seeking 0 → ascending reproduces the render's own seek order.
-  const fractions = Array.from({ length: k }, (_, i) => (i + 1) / (k + 1));
+  const fractions = computeDeVerifySampleFractions(k);
   const seekTo = async (t: number): Promise<void> => {
     await page.evaluate((tt: number) => {
       const hf = (

diff --git a/packages/producer/src/services/htmlCompiler.test.ts b/packages/producer/src/services/htmlCompiler.test.ts
@@ -8,6 +8,7 @@ import {
   collectExternalAssets,
   compileForRender,
   injectSdkPositionEditsRenderScript,
+  detectAncestorBackgroundImage,
   detectRenderModeHints,
   detectShaderTransitionUsage,
   detectThreeDTransformUsage,
@@ -718,6 +719,65 @@ describe("detectThreeDTransformUsage", () => {
   });
 });
 
+describe("detectAncestorBackgroundImage", () => {
+  const wrap = (headCss: string, bodyAttrs = "", inner = "") =>
+    `<!doctype html><html><head><style>${headCss}</style></head><body${bodyAttrs ? ` ${bodyAttrs}` : ""}>` +
+    `<div id="root" data-composition-id="main" data-duration="10">${inner}</div></body></html>`;
+
+  it("detects a linear-gradient body background from a style rule", () => {
+    expect(
+      detectAncestorBackgroundImage(
+        wrap("body { background: linear-gradient(135deg, #1b2735, #090a0f); }"),
+      ),
+    ).toBe(true);
+  });
+
+  it("detects a url() background-image on html", () => {
+    expect(detectAncestorBackgroundImage(wrap('html { background-image: url("bg.png"); }'))).toBe(
+      true,
+    );
+  });
+
+  it("detects an inline gradient style on body", () => {
+    expect(
+      detectAncestorBackgroundImage(
+        wrap("", 'style="background: radial-gradient(circle, #111, #000)"'),
+      ),
+    ).toBe(true);
+  });
+
+  it("detects a class-selected wrapper between body and the root", () => {
+    const html =
+      "<!doctype html><html><head><style>.page-bg { background-image: linear-gradient(#111, #000); }</style></head>" +
+      '<body><div class="page-bg"><div data-composition-id="main" data-duration="10"></div></div></body></html>';
+    expect(detectAncestorBackgroundImage(html)).toBe(true);
+  });
+
+  it("ignores background-image on elements inside the composition root", () => {
+    expect(
+      detectAncestorBackgroundImage(
+        wrap(
+          "#hero { background-image: linear-gradient(#111, #000); }",
+          "",
+          '<div id="hero"></div>',
+        ),
+      ),
+    ).toBe(false);
+  });
+
+  it("ignores plain background-color ancestors", () => {
+    expect(detectAncestorBackgroundImage(wrap("html, body { background: #0d1117; }"))).toBe(false);
+  });
+
+  it("returns false without a composition root", () => {
+    expect(
+      detectAncestorBackgroundImage(
+        "<html><head><style>body { background: linear-gradient(#111, #000); }</style></head><body></body></html>",
+      ),
+    ).toBe(false);
+  });
+});
+
 describe("detectShaderTransitionUsage", () => {
   it("detects authored HyperShader initialization", () => {
     const html = `<!doctype html>

diff --git a/packages/producer/src/services/htmlCompiler.ts b/packages/producer/src/services/htmlCompiler.ts
@@ -78,6 +78,8 @@ export interface CompiledComposition {
   usesThreeDTransforms: boolean;
   /** Author HTML/CSS use mix-blend-mode (pre-CDN-inline scan). */
   usesMixBlendMode: boolean;
+  /** Ancestors of the composition root carry a background-image (gradient/url). */
+  hasAncestorBackgroundImage: boolean;
 }
 
 /** Adapts linkedom's `parseHTML` to the `checkSubCompositionUsability` contract. */
@@ -324,6 +326,64 @@ function detectMixBlendModeUsage(html: string): boolean {
   return MIX_BLEND_MODE_PATTERN.test(html);
 }
 
+/** A background declaration whose value paints an image (gradient or url). */
+const BACKGROUND_IMAGE_DECL_PATTERN =
+  /(?:^|;|\{)\s*background(?:-image)?\s*:[^;}]*(?:\bgradient\s*\(|url\s*\()/i;
+
+/**
+ * Background-image signals on ancestors of the composition root.
+ * drawElementImage only paints the captured subtree; drawElementService's
+ * per-frame ancestor fill replicates what lies behind it by walking up the
+ * DOM for the nearest non-transparent `backgroundColor`. A background-IMAGE
+ * (linear-gradient, url) on <body>/<html>/a wrapper reads as transparent in
+ * that scan, so a deeper ancestor's solid color paints instead — measured:
+ * a body `linear-gradient` replaced by the html background color wherever
+ * the subtree left pixels uncovered (30.9 dB min vs baseline), and the
+ * damage can set in late enough to slip past the self-verify sample grid.
+ * Backgrounds on elements INSIDE the root are painted correctly and are
+ * deliberately not matched — this walks only the root's ancestor chain and
+ * the style rules that select into it.
+ */
+export function detectAncestorBackgroundImage(html: string): boolean {
+  const { document } = parseHTML(html);
+  const root = document.querySelector("[data-composition-id]");
+  if (!root) return false;
+  const ancestors: Element[] = [];
+  for (let el = root.parentElement; el; el = el.parentElement) ancestors.push(el);
+  if (document.documentElement && !ancestors.includes(document.documentElement)) {
+    ancestors.push(document.documentElement);
+  }
+  // Inline styles on the ancestor chain.
+  for (const el of ancestors) {
+    const style = el.getAttribute("style");
+    if (style && BACKGROUND_IMAGE_DECL_PATTERN.test(`{${style}}`)) return true;
+  }
+  // <style> rules: any rule carrying an image-painting background declaration
+  // whose selector resolves to an ancestor of the root. Selector matching goes
+  // through querySelectorAll so class/id/compound selectors on wrappers are
+  // covered, not just literal `body`/`html`.
+  for (const styleEl of document.querySelectorAll("style")) {
+    const css = styleEl.textContent ?? "";
+    for (const rule of css.matchAll(/([^{}]+)\{([^}]*)\}/g)) {
+      const [, selectorList = "", declarations = ""] = rule;
+      if (!BACKGROUND_IMAGE_DECL_PATTERN.test(`{${declarations}}`)) continue;
+      for (const selector of selectorList.split(",")) {
+        const sel = selector.trim();
+        if (!sel || sel.startsWith("@")) continue;
+        if (/^(?:html|:root)$/i.test(sel)) return true;
+        try {
+          for (const matched of document.querySelectorAll(sel)) {
+            if (ancestors.includes(matched)) return true;
+          }
+        } catch {
+          // Selector syntax linkedom can't parse (e.g. vendor pseudo) — skip.
+        }
+      }
+    }
+  }
+  return false;
+}
+
 const SHADER_TRANSITION_USAGE_PATTERN =
   /\b(?:(?:window|globalThis)\s*\.\s*)?HyperShader\s*\.\s*init\s*\(|\b__hf\s*\.\s*transitions\s*=/;
 
@@ -1706,6 +1766,7 @@ export async function compileForRender(
   // composition that loads GSAP from a CDN.
   const usesThreeDTransforms = detectThreeDTransformUsage(sanitizedHtml);
   const usesMixBlendMode = detectMixBlendModeUsage(sanitizedHtml);
+  const hasAncestorBackgroundImage = detectAncestorBackgroundImage(sanitizedHtml);
 
   const normalizedFontHtml = normalizeSystemFontPrimaryFamilies(
     injectTextRenderingRule(
@@ -1881,6 +1942,7 @@ export async function compileForRender(
     hasShaderTransitions,
     usesThreeDTransforms,
     usesMixBlendMode,
+    hasAncestorBackgroundImage,
   };
 }
 

diff --git a/packages/producer/src/services/render/stages/compileStage.ts b/packages/producer/src/services/render/stages/compileStage.ts
@@ -200,6 +200,28 @@ export async function runCompileStage(input: CompileStageInput): Promise<Compile
         "for this render. Capture uses the platform's baseline route.",
     );
   }
+  // Fast-capture ancestor-background-image gate, same shape as the gates above.
+  // drawElementService's per-frame ancestor fill replicates only the nearest
+  // non-transparent ancestor background-COLOR behind the captured subtree; a
+  // background-image (linear-gradient, url) on <body>/<html>/a wrapper reads
+  // as transparent there, so a deeper ancestor's solid color paints instead
+  // wherever the subtree leaves pixels uncovered (measured: body gradient
+  // replaced by html color, 30.9 dB min vs baseline — and late-onset, so the
+  // self-verify grid can miss it). HF_FAST_CAPTURE_ANCESTOR_BG=true bypasses
+  // for R&D.
+  if (
+    cfg.useDrawElement &&
+    process.env.HF_FAST_CAPTURE_ANCESTOR_BG !== "true" &&
+    compiled.hasAncestorBackgroundImage
+  ) {
+    cfg.useDrawElement = false;
+    deCompileGate = "ancestor_background_image";
+    log.info(
+      "[Render] Fast capture: composition root's ancestors (body/html/wrapper) carry a " +
+        "background-image — disabling drawElementImage for this render. Capture uses the " +
+        "platform's baseline route.",
+    );
+  }
   // Shader-transition comps: page-side compositing is the faster, purpose-built
   // path for them, and resolveConfig force-disables it whenever drawElement is
   // on. With drawElement default-on that trade is backwards — prefer page-side