fix(producer): advance a sped-up clip's file clock by the source time it played

When opacity raises an auto-start clip's start, the encoder's in-point moved
by the timeline delta, as if the clip plays at 1x. Integrate the clip's rate
over that delta instead, and shift a rate lane to the new start.

Author: valeriangalliat

packages/producer/src/services/render/stages/probeStage.test.ts

@@ -14,6 +14,7 @@ import { collectRenderMedia } from "../../renderMediaCollector.js";
 const workDir = mkdtempSync(join(tmpdir(), "hf-stage-test-"));
 afterAll(() => rmSync(workDir, { recursive: true, force: true }));
 import { createHash } from "node:crypto";
+import { shiftRateLane, sourceTimeAt } from "@hyperframes/core";
 import {
   hasAutoStartVideos,
   hasScriptedAudioVolumeAutomation,
@@ -981,6 +982,62 @@ describe("runProbeStage — forceScreenshot threading", () => {
     );
   });
 
+  it("shifts auto-start mediaStart by the source time a sped-up clip played", async () => {
+    resetRetryMocks();
+    visibilityWindows = [{ videoId: "clip", visibleStart: 3.5, visibleEnd: 6 }];
+    const { runProbeStage } = await import("./probeStage.js");
+    const input = makeProbeInput({});
+    input.composition.videos.push({
+      id: "clip",
+      src: "runtime.mp4",
+      start: 2,
+      end: 6,
+      mediaStart: 0,
+      playbackRate: 2,
+      loop: false,
+      hasAudio: false,
+    });
+    input.compiled.html = `<video id="clip" src="runtime.mp4" data-hf-auto-start=""></video>`;
+
+    await runProbeStage(input);
+
+    expect(input.composition.videos[0]).toEqual(
+      expect.objectContaining({ id: "clip", start: 3.5, end: 6, mediaStart: 3, playbackRate: 2 }),
+    );
+  });
+
+  it("shifts a rate lane to the raised start", async () => {
+    resetRetryMocks();
+    visibilityWindows = [{ videoId: "clip", visibleStart: 3, visibleEnd: 6 }];
+    const { runProbeStage } = await import("./probeStage.js");
+    const input = makeProbeInput({});
+    const lane = {
+      target: "rate",
+      points: [
+        { t: 0, v: 1 },
+        { t: 2, v: 3 },
+      ],
+    } satisfies RateSpec;
+    input.composition.videos.push({
+      id: "clip",
+      src: "runtime.mp4",
+      start: 2,
+      end: 6,
+      mediaStart: 0,
+      playbackRate: lane,
+      loop: false,
+      hasAudio: false,
+    });
+    input.compiled.html = `<video id="clip" src="runtime.mp4" data-hf-auto-start=""></video>`;
+
+    await runProbeStage(input);
+
+    const video = input.composition.videos[0]!;
+    expect(video.start).toBe(3);
+    expect(video.mediaStart).toBeCloseTo(sourceTimeAt(lane, 1), 9);
+    expect(video.playbackRate).toEqual(shiftRateLane(lane, 1));
+  });
+
   it("leaves mediaStart at 0 when visibility raises start on an empty-src video", async () => {
     resetRetryMocks();
     visibilityWindows = [{ videoId: "clip", visibleStart: 3.5, visibleEnd: 6 }];

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

@@ -800,7 +800,10 @@ export async function runProbeStage(input: ProbeStageInput): Promise<ProbeStageR
             video.end = win.visibleEnd;
             const raised = video.start - prevStart;
             if (raised > 0 && video.mediaStart <= 0 && hostClockIds.has(video.id)) {
-              video.mediaStart += raised;
+              const rate = normalizeRateSpec(video.playbackRate);
+              video.mediaStart += sourceTimeAt(rate, raised);
+              if (video.playbackRate !== undefined)
+                video.playbackRate = shiftRateLane(rate, raised);
             }
             const duration = video.end - prevStart;
             if (duration > 0) {