fix(engine): defend macOS regular Chrome screenshots

packages/engine/src/services/frameCapture.captureOptions.test.ts

@@ -0,0 +1,36 @@
+// @vitest-environment node
+import { describe, expect, it } from "vitest";
+import { resolveCaptureSessionOptions } from "./frameCapture.js";
+
+describe("createCaptureSession captureBeyondViewport defaults", () => {
+  it("plumbs the macOS regular-Chrome default into returned session options", () => {
+    const options = resolveCaptureSessionOptions(
+      {
+        width: 1920,
+        height: 1080,
+        fps: { num: 30, den: 1 },
+        format: "jpeg",
+      },
+      "Chrome/149.0.7827.155",
+      "darwin",
+    );
+
+    expect(options.captureBeyondViewport).toBe(true);
+  });
+
+  it("preserves explicit caller overrides", () => {
+    const options = resolveCaptureSessionOptions(
+      {
+        width: 1920,
+        height: 1080,
+        fps: { num: 30, den: 1 },
+        format: "jpeg",
+        captureBeyondViewport: false,
+      },
+      "Chrome/149.0.7827.155",
+      "darwin",
+    );
+
+    expect(options.captureBeyondViewport).toBe(false);
+  });
+});

packages/engine/src/services/frameCapture.ts

@@ -28,6 +28,7 @@ import {
   getCdpSession,
   pageScreenshotCapture,
   initTransparentBackground,
+  shouldDefaultCaptureBeyondViewport,
 } from "./screenshotService.js";
 import { DEFAULT_CONFIG, type EngineConfig } from "../config.js";
 import type {
@@ -310,6 +311,18 @@ export async function driveWarmupTicks(
   }
 }
 
+export function resolveCaptureSessionOptions(
+  options: CaptureOptions,
+  browserVersion: string,
+  platform: NodeJS.Platform = process.platform,
+): CaptureOptions {
+  return {
+    ...options,
+    captureBeyondViewport:
+      options.captureBeyondViewport ?? shouldDefaultCaptureBeyondViewport(browserVersion, platform),
+  };
+}
+
 async function waitForCloseWithTimeout(promise: Promise<unknown>): Promise<boolean> {
   let timedOut = false;
   let timer: ReturnType<typeof setTimeout> | undefined;
@@ -417,6 +430,7 @@ export async function createCaptureSession(
     }, variablesJson);
   }
   const browserVersion = await browser.version();
+  const sessionOptions = resolveCaptureSessionOptions(options, browserVersion);
   const expectedMajor = config?.expectedChromiumMajor;
   if (Number.isFinite(expectedMajor)) {
     const actualChromiumMajor = Number.parseInt(
@@ -430,9 +444,9 @@ export async function createCaptureSession(
     }
   }
   const viewport: Viewport = {
-    width: options.width,
-    height: options.height,
-    deviceScaleFactor: options.deviceScaleFactor || 1,
+    width: sessionOptions.width,
+    height: sessionOptions.height,
+    deviceScaleFactor: sessionOptions.deviceScaleFactor || 1,
   };
   await page.setViewport(viewport);
 
@@ -446,7 +460,7 @@ export async function createCaptureSession(
   return {
     browser,
     page,
-    options,
+    options: sessionOptions,
     serverUrl,
     outputDir,
     onBeforeCapture,

packages/engine/src/services/screenshotService.test.ts

@@ -7,6 +7,7 @@ import {
   cdpSessionCache,
   injectVideoFramesBatch,
   syncVideoFrameVisibility,
+  shouldDefaultCaptureBeyondViewport,
 } from "./screenshotService.js";
 
 // Stub a Page + CDPSession just enough that pageScreenshotCapture can call
@@ -121,6 +122,22 @@ describe("pageScreenshotCapture supersample plumbing", () => {
   });
 });
 
+describe("shouldDefaultCaptureBeyondViewport", () => {
+  it("guards regular Chrome on macOS", () => {
+    expect(shouldDefaultCaptureBeyondViewport("Chrome/149.0.7827.155", "darwin")).toBe(true);
+  });
+
+  it("keeps chrome-headless-shell on the faster viewport-bound path", () => {
+    expect(shouldDefaultCaptureBeyondViewport("HeadlessChrome/148.0.7778.97", "darwin")).toBe(
+      false,
+    );
+  });
+
+  it("does not change regular Chrome defaults on non-macOS platforms", () => {
+    expect(shouldDefaultCaptureBeyondViewport("Chrome/149.0.7827.155", "linux")).toBe(false);
+  });
+});
+
 describe("injectVideoFramesBatch replacement layout", () => {
   it("does not copy opposing inset constraints onto the injected frame image", async () => {
     const { window, document } = parseHTML(

packages/engine/src/services/screenshotService.ts

@@ -19,6 +19,17 @@ export async function getCdpSession(page: Page): Promise<import("puppeteer-core"
   return client;
 }
 
+export function shouldDefaultCaptureBeyondViewport(
+  browserVersion: string,
+  platform: NodeJS.Platform = process.platform,
+): boolean {
+  // Regular Chrome's viewport-bound screenshot path can expose a compositor
+  // surface shorter than the page viewport on affected macOS builds. In that
+  // case Chrome fills the clipped area with the page background. Headless shell
+  // reports as HeadlessChrome and keeps the faster viewport-bound path.
+  return platform === "darwin" && browserVersion.startsWith("Chrome/");
+}
+
 /**
  * BeginFrame result with screenshot data and damage detection.
  */

packages/engine/src/types.ts

@@ -93,10 +93,11 @@ export interface CaptureOptions {
   quality?: number;
   deviceScaleFactor?: number;
   /**
-   * Opt into Chrome's capture-beyond-viewport screenshot path. Keep this off
-   * for ordinary viewport-sized captures because it is substantially slower in
-   * Chrome's screenshot compositor path. Enable for known compositor edge cases
-   * such as native video surfaces in tall portrait renders.
+   * Opt into Chrome's capture-beyond-viewport screenshot path. Leave undefined
+   * to let the engine pick the safe browser-specific default. Pass false only
+   * when the caller explicitly wants Chrome's faster viewport-bound path.
+   * Enable for known compositor edge cases such as native video surfaces in
+   * tall portrait renders.
    */
   captureBeyondViewport?: boolean;
   /**

packages/producer/src/services/distributed/renderChunk.ts

@@ -507,7 +507,7 @@ export async function renderChunk(
       // declare `data-composition-variables` leave this undefined and the
       // engine skips the `evaluateOnNewDocument` injection.
       variables: encoder.variables,
-      captureBeyondViewport: (planVideos?.videos.length ?? 0) > 0,
+      ...((planVideos?.videos.length ?? 0) > 0 ? { captureBeyondViewport: true } : {}),
       // lock the BeginFrame warmup loop to a fixed iteration count so
       // `beginFrameTimeTicks` is host-independent. Only chunks ever set this.
       lockWarmupTicks: true,

packages/producer/src/services/render/stages/captureStage.ts

@@ -126,6 +126,8 @@ export interface CaptureStageResult {
   probeSession: CaptureSession | null;
   /** Browser console buffer from whichever session was active last. */
   lastBrowserConsole: string[];
+  /** Engine-resolved screenshot flag from the consumed sequential/probe session, when observed. */
+  captureBeyondViewport?: boolean;
 }
 
 export async function runCaptureStage(input: CaptureStageInput): Promise<CaptureStageResult> {
@@ -150,6 +152,7 @@ export async function runCaptureStage(input: CaptureStageInput): Promise<Capture
   } = input;
   let { workerCount, probeSession } = input;
   let lastBrowserConsole: string[] = [];
+  let captureBeyondViewport: boolean | undefined = probeSession?.options.captureBeyondViewport;
 
   // Derive a local cfg view rather than reading `forceScreenshot` from the
   // caller-owned `cfg`. The sequencer threads the resolved value via the
@@ -228,6 +231,7 @@ export async function runCaptureStage(input: CaptureStageInput): Promise<Capture
       workerCount = lastAttempt.workers;
     }
     if (probeSession) {
+      captureBeyondViewport = probeSession.options.captureBeyondViewport;
       lastBrowserConsole = probeSession.browserConsoleBuffer;
       await closeCaptureSession(probeSession);
       probeSession = null;
@@ -245,6 +249,7 @@ export async function runCaptureStage(input: CaptureStageInput): Promise<Capture
         videoInjector,
         captureCfg,
       ));
+    captureBeyondViewport = session.options.captureBeyondViewport;
     if (probeSession) {
       prepareCaptureSessionForReuse(session, framesDir, videoInjector);
       probeSession = null;
@@ -304,5 +309,5 @@ export async function runCaptureStage(input: CaptureStageInput): Promise<Capture
     }
   }
 
-  return { workerCount, probeSession, lastBrowserConsole };
+  return { workerCount, probeSession, lastBrowserConsole, captureBeyondViewport };
 }

packages/producer/src/services/render/stages/captureStreamingStage.ts

@@ -126,6 +126,8 @@ export type CaptureStreamingStageResult =
       probeSession: CaptureSession | null;
       lastBrowserConsole: string[];
       workerCount: number;
+      /** Engine-resolved screenshot flag from the consumed sequential/probe session, when observed. */
+      captureBeyondViewport?: boolean;
     }
   | {
       /** Spawn failed (non-abort) — sequencer should fall back to the disk path. */
@@ -156,6 +158,7 @@ export async function runCaptureStreamingStage(
   } = input;
   let { workerCount, probeSession } = input;
   let lastBrowserConsole: string[] = [];
+  let captureBeyondViewport: boolean | undefined = probeSession?.options.captureBeyondViewport;
 
   // Derive a local cfg view rather than reading `forceScreenshot` from the
   // caller-owned `cfg`. The sequencer threads the resolved value via the
@@ -241,6 +244,7 @@ export async function runCaptureStreamingStage(
       pushWorkerDedupPerfs(workerResults, dedupPerfs);
 
       if (probeSession) {
+        captureBeyondViewport = probeSession.options.captureBeyondViewport;
         lastBrowserConsole = probeSession.browserConsoleBuffer;
         await closeCaptureSession(probeSession);
         probeSession = null;
@@ -258,6 +262,7 @@ export async function runCaptureStreamingStage(
           videoInjector,
           captureCfg,
         ));
+      captureBeyondViewport = session.options.captureBeyondViewport;
       if (probeSession) {
         prepareCaptureSessionForReuse(session, framesDir, videoInjector);
         probeSession = null;
@@ -325,6 +330,7 @@ export async function runCaptureStreamingStage(
       probeSession,
       lastBrowserConsole,
       workerCount,
+      captureBeyondViewport,
     };
   } finally {
     // Defensive cleanup: if the streaming branch threw before

packages/producer/src/services/renderOrchestrator.ts

@@ -1074,6 +1074,10 @@ export async function executeRenderJob(
     fileServer = probeResult.fileServer;
     probeSession = probeResult.probeSession;
     lastBrowserConsole = probeResult.lastBrowserConsole;
+    let resolvedCaptureBeyondViewport = probeSession?.options.captureBeyondViewport;
+    if (resolvedCaptureBeyondViewport !== undefined) {
+      updateCaptureObservability({ captureBeyondViewport: resolvedCaptureBeyondViewport });
+    }
     // The probe stage produces `duration` / `totalFrames` values; the
     // sequencer owns the `RenderJob` and writes them onto it.
     job.duration = probeResult.duration;
@@ -1213,11 +1217,13 @@ export async function executeRenderJob(
       quality: needsAlpha ? undefined : job.config.quality === "draft" ? 80 : 95,
       variables: job.config.variables,
       deviceScaleFactor,
-      captureBeyondViewport: composition.videos.length > 0,
+      ...(composition.videos.length > 0 ? { captureBeyondViewport: true } : {}),
     };
-    updateCaptureObservability({
-      captureBeyondViewport: captureOptions.captureBeyondViewport ?? false,
-    });
+    resolvedCaptureBeyondViewport =
+      captureOptions.captureBeyondViewport ?? resolvedCaptureBeyondViewport;
+    if (resolvedCaptureBeyondViewport !== undefined) {
+      updateCaptureObservability({ captureBeyondViewport: resolvedCaptureBeyondViewport });
+    }
 
     // Capture sessions do not need native browser metadata for videos whose
     // pixels come from out-of-band FFmpeg frame extraction. Waiting on those
@@ -1442,7 +1448,7 @@ export async function executeRenderJob(
     observability.checkpoint("capture_strategy", "resolved", {
       workerCount,
       forceScreenshot: captureForceScreenshot,
-      captureBeyondViewport: captureOptions.captureBeyondViewport ?? false,
+      captureBeyondViewport: resolvedCaptureBeyondViewport ?? null,
       useStreamingEncode,
       useLayeredComposite,
       usePageSideCompositing: usePageSideCompositingForTransitions,
@@ -1592,6 +1598,11 @@ export async function executeRenderJob(
           streamingHandled = true;
           workerCount = streamingRes.workerCount;
           updateCaptureObservability({ workerCount });
+          if (streamingRes.captureBeyondViewport !== undefined) {
+            updateCaptureObservability({
+              captureBeyondViewport: streamingRes.captureBeyondViewport,
+            });
+          }
           probeSession = streamingRes.probeSession;
           lastBrowserConsole = streamingRes.lastBrowserConsole;
           perfStages.captureMs = Date.now() - stage4Start;
@@ -1637,6 +1648,11 @@ export async function executeRenderJob(
         const captureFrameMs = Date.now() - captureFrameStart;
         workerCount = captureRes.workerCount;
         updateCaptureObservability({ workerCount });
+        if (captureRes.captureBeyondViewport !== undefined) {
+          updateCaptureObservability({
+            captureBeyondViewport: captureRes.captureBeyondViewport,
+          });
+        }
         probeSession = captureRes.probeSession;
         lastBrowserConsole = captureRes.lastBrowserConsole;
 

packages/producer/tests/chrome-screenshot-bottom-edge/meta.json

@@ -0,0 +1,13 @@
+{
+  "name": "chrome-screenshot-bottom-edge",
+  "description": "Regression guard for screenshot capture leaking page background into the bottom of a viewport-sized MP4. The composition paints a red page background below full-frame content so any bottom-edge capture gap collapses PSNR.",
+  "tags": ["regression", "screenshot", "edge"],
+  "minPsnr": 30,
+  "maxFrameFailures": 0,
+  "minAudioCorrelation": 0,
+  "maxAudioLagWindows": 1,
+  "renderConfig": {
+    "fps": 12,
+    "workers": 1
+  }
+}