diff --git a/packages/cli/src/commands/init.test.ts b/packages/cli/src/commands/init.test.ts
index 47f23bc19e..13a86b0901 100644
--- a/packages/cli/src/commands/init.test.ts
+++ b/packages/cli/src/commands/init.test.ts
@@ -4,7 +4,11 @@ import { existsSync, mkdirSync, mkdtempSync, readFileSync, rmSync, writeFileSync
 import { tmpdir } from "node:os";
 import { join, resolve } from "node:path";
 import { fileURLToPath } from "node:url";
-import { applyResolutionPreset, injectTailwindBrowserScript } from "./init.js";
+import {
+  applyResolutionPreset,
+  injectTailwindBrowserScript,
+  resolveVideoDurationSeconds,
+} from "./init.js";
 
 const cliEntry = resolve(fileURLToPath(import.meta.url), "..", "..", "cli.ts");
 const tailwindScript =
@@ -177,6 +181,26 @@ describe("hyperframes init flag rename", () => {
     }
   });
 
+  it("uses the video stream duration when audio outlasts the final video frame", () => {
+    expect(
+      resolveVideoDurationSeconds({
+        streamDuration: 1,
+        frameDuration: 1,
+        formatDuration: 1.2,
+      }),
+    ).toBe(1);
+  });
+
+  it("falls through unusable stream durations before using the container duration", () => {
+    expect(
+      resolveVideoDurationSeconds({
+        streamDuration: 0,
+        frameDuration: Number.NaN,
+        formatDuration: 1.2,
+      }),
+    ).toBe(1.2);
+  });
+
   it("--audio with a missing file fails without creating the project directory", () => {
     const dir = mkdtempSync(join(tmpdir(), "hf-init-test-"));
     const target = join(dir, "proj");
diff --git a/packages/cli/src/commands/init.ts b/packages/cli/src/commands/init.ts
index 7b058673ec..921320d68d 100644
--- a/packages/cli/src/commands/init.ts
+++ b/packages/cli/src/commands/init.ts
@@ -81,6 +81,22 @@ const TAILWIND_BROWSER_SRC = `https://cdn.jsdelivr.net/npm/@tailwindcss/browser@
 const TAILWIND_BROWSER_INTEGRITY =
   "sha384-v5YF9xS+gLRWdvrQ0u/WRbCkjSIH0NjHIPe8tBL1ZRrmI7PiSH6LLdzs0aAIMCuh";
 
+export function resolveVideoDurationSeconds({
+  streamDuration,
+  frameDuration,
+  formatDuration,
+}: {
+  streamDuration: number;
+  frameDuration: number;
+  formatDuration: number;
+}): number {
+  return (
+    [streamDuration, frameDuration, formatDuration].find(
+      (duration) => Number.isFinite(duration) && duration > 0,
+    ) ?? DEFAULT_META.durationSeconds
+  );
+}
+
 // ---------------------------------------------------------------------------
 // ffprobe helper — shells out to ffprobe to avoid engine dependency
 // ---------------------------------------------------------------------------
@@ -103,6 +119,8 @@ function probeVideo(filePath: string): VideoMeta | undefined {
         height?: number;
         r_frame_rate?: string;
         avg_frame_rate?: string;
+        duration?: string;
+        nb_frames?: string;
       }[];
       format?: { duration?: string };
     } = JSON.parse(raw);
@@ -124,11 +142,18 @@ function probeVideo(filePath: string): VideoMeta | undefined {
       }
     }
 
-    const durationStr = parsed.format?.duration;
-    const durationSeconds = durationStr !== undefined ? parseFloat(durationStr) : 5;
+    const streamDuration = parseFloat(videoStream.duration ?? "");
+    const frameCount = parseInt(videoStream.nb_frames ?? "", 10);
+    const frameDuration = Number.isFinite(frameCount) && fps > 0 ? frameCount / fps : NaN;
+    const formatDuration = parseFloat(parsed.format?.duration ?? "");
+    const durationSeconds = resolveVideoDurationSeconds({
+      streamDuration,
+      frameDuration,
+      formatDuration,
+    });
 
     return {
-      durationSeconds: Number.isNaN(durationSeconds) ? 5 : durationSeconds,
+      durationSeconds,
       width: videoStream.width ?? 1920,
       height: videoStream.height ?? 1080,
       fps,
diff --git a/packages/core/src/runtime/init.test.ts b/packages/core/src/runtime/init.test.ts
index 340456850c..4cd177442b 100644
--- a/packages/core/src/runtime/init.test.ts
+++ b/packages/core/src/runtime/init.test.ts
@@ -325,6 +325,33 @@ describe("initSandboxRuntimeModular", () => {
     expect(child.style.visibility).toBe("hidden");
   });
 
+  it("uses a half-open interval around a timed element's end boundary", () => {
+    const root = document.createElement("div");
+    root.setAttribute("data-composition-id", "main");
+    root.setAttribute("data-root", "true");
+    root.setAttribute("data-start", "0");
+    root.setAttribute("data-width", "1920");
+    root.setAttribute("data-height", "1080");
+    document.body.appendChild(root);
+
+    const clip = document.createElement("div");
+    clip.setAttribute("data-start", "0");
+    clip.setAttribute("data-duration", "2.5");
+    root.appendChild(clip);
+
+    window.__timelines = { main: createMockTimeline(5) };
+    initSandboxRuntimeModular();
+
+    window.__player?.renderSeek(2.5 - 1e-9);
+    expect(clip.style.visibility).toBe("visible");
+
+    window.__player?.renderSeek(2.5);
+    expect(clip.style.visibility).toBe("hidden");
+
+    window.__player?.renderSeek(2.5 + 1e-9);
+    expect(clip.style.visibility).toBe("hidden");
+  });
+
   it("keeps external composition hosts visible through their authored duration", async () => {
     const root = document.createElement("div");
     root.setAttribute("data-composition-id", "main");
diff --git a/packages/core/src/runtime/init.ts b/packages/core/src/runtime/init.ts
index 24fb83cb57..d2317f6e59 100644
--- a/packages/core/src/runtime/init.ts
+++ b/packages/core/src/runtime/init.ts
@@ -583,7 +583,7 @@ export function initSandboxRuntimeModular(): void {
     const computedEnd =
       duration != null && duration > 0 ? start + duration : Number.POSITIVE_INFINITY;
     return (
-      currentTime >= start && (Number.isFinite(computedEnd) ? currentTime <= computedEnd : true)
+      currentTime >= start && (Number.isFinite(computedEnd) ? currentTime < computedEnd : true)
     );
   };
 
@@ -2813,7 +2813,7 @@ export function initSandboxRuntimeModular(): void {
             const mediaStart =
               Number.parseFloat(rawEl.dataset.playbackStart ?? rawEl.dataset.mediaStart ?? "0") ||
               0;
-            if (Number.isFinite(start) && state.currentTime >= start && state.currentTime <= end) {
+            if (Number.isFinite(start) && state.currentTime >= start && state.currentTime < end) {
               if (!rawEl.paused) {
                 clock.attachAudioSource({ el: rawEl, compositionStart: start, mediaStart });
                 foundActive = true;
diff --git a/packages/core/src/runtime/media.test.ts b/packages/core/src/runtime/media.test.ts
index bd15db9942..63843be906 100644
--- a/packages/core/src/runtime/media.test.ts
+++ b/packages/core/src/runtime/media.test.ts
@@ -250,6 +250,28 @@ describe("syncRuntimeMedia", () => {
     expect(clip.el.play).toHaveBeenCalled();
   });
 
+  it("uses a half-open interval around a clip's end boundary", () => {
+    const clip = createMockClip({ start: 0, end: 2.5 });
+    Object.defineProperty(clip.el, "readyState", { value: 4, writable: true });
+
+    syncRuntimeMedia({
+      clips: [clip],
+      timeSeconds: 2.5 - 1e-9,
+      playing: true,
+      playbackRate: 1,
+    });
+    expect(clip.el.play).toHaveBeenCalledTimes(1);
+
+    syncRuntimeMedia({ clips: [clip], timeSeconds: 2.5, playing: true, playbackRate: 1 });
+    syncRuntimeMedia({
+      clips: [clip],
+      timeSeconds: 2.5 + 1e-9,
+      playing: true,
+      playbackRate: 1,
+    });
+    expect(clip.el.play).toHaveBeenCalledTimes(1);
+  });
+
   it("plays synchronously even when media is unbuffered (preserves user gesture)", () => {
     // Calling play() synchronously inside the user-gesture call chain lets the
     // browser queue playback until data buffers, while consuming the transient
diff --git a/packages/core/src/runtime/media.ts b/packages/core/src/runtime/media.ts
index aa8e1b71da..2214588558 100644
--- a/packages/core/src/runtime/media.ts
+++ b/packages/core/src/runtime/media.ts
@@ -173,7 +173,7 @@ export function syncRuntimeMedia(params: {
     // (el.ended resets to false when the user scrubs back, so seeks work.)
     const isActive =
       params.timeSeconds >= clip.start &&
-      params.timeSeconds <= clip.end &&
+      params.timeSeconds < clip.end &&
       relTime >= 0 &&
       (!el.ended || clip.loop);
     if (isActive) {
diff --git a/packages/producer/tests/style-7-prod/output/output.mp4 b/packages/producer/tests/style-7-prod/output/output.mp4
index 42facdf17d..114442522e 100644
--- a/packages/producer/tests/style-7-prod/output/output.mp4
+++ b/packages/producer/tests/style-7-prod/output/output.mp4
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:07aebceb20c5963e7a2feb392a564e2f592c39490dba1f6af07bb08b6a3c63d8
-size 12267006
+oid sha256:74c710f61ae3400ecc5477e9ab42fa78c25340e6947b8dc5e0a916da166620e4
+size 12282546