🎵 Add PortalAudioManager component for background music

- Add PortalAudioManager.tsx with background music fade in/out
  - 1 second fade-in at the beginning
  - 3 second fade-out at the end
  - Base volume at 0.25 (25%)
- Integrate PortalAudioManager into PortalPresentation
- Add PortalOutroScene to PortalPresentation (was using placeholder)
- Add comprehensive tests for PortalAudioManager (13 tests)
  - Tests for volume at various frames
  - Tests for fade-in/fade-out behavior
  - Integration tests

Scene-specific SFX remain in individual scene components for
better timing accuracy and maintainability.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

videos/src/PortalPresentation.tsx

@@ -7,6 +7,8 @@ import { MeetupShowcaseScene } from "./scenes/portal/MeetupShowcaseScene";
 import { TopMeetupsScene } from "./scenes/portal/TopMeetupsScene";
 import { ActivityFeedScene } from "./scenes/portal/ActivityFeedScene";
 import { CallToActionScene } from "./scenes/portal/CallToActionScene";
+import { PortalOutroScene } from "./scenes/portal/PortalOutroScene";
+import { PortalAudioManager } from "./components/PortalAudioManager";
 
 /**
  * PortalPresentation - Main composition for the Einundzwanzig Portal presentation video
@@ -119,6 +121,9 @@ export const PortalPresentation: React.FC = () => {
       className="bg-gradient-to-br from-zinc-900 to-zinc-800"
       style={{ fontFamily: inconsolataFont }}
     >
+      {/* Background Music with fade in/out */}
+      <PortalAudioManager />
+
       {/* Wallpaper Background */}
       <Img
         src={staticFile("einundzwanzig-wallpaper.png")}
@@ -203,7 +208,7 @@ export const PortalPresentation: React.FC = () => {
         durationInFrames={sceneFrames.outro.duration}
         premountFor={fps}
       >
-        <PlaceholderScene name="Outro" sceneNumber={9} />
+        <PortalOutroScene />
       </Sequence>
     </AbsoluteFill>
   );

videos/src/components/PortalAudioManager.test.tsx

@@ -0,0 +1,233 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
+import { render, cleanup } from "@testing-library/react";
+import { PortalAudioManager } from "./PortalAudioManager";
+
+/* eslint-disable @remotion/warn-native-media-tag */
+// Mock Remotion hooks with dynamic frame value
+let mockCurrentFrame = 45;
+
+vi.mock("remotion", () => ({
+  useCurrentFrame: vi.fn(() => mockCurrentFrame),
+  useVideoConfig: vi.fn(() => ({
+    fps: 30,
+    width: 1920,
+    height: 1080,
+    durationInFrames: 2700, // 90 seconds at 30fps
+  })),
+  interpolate: vi.fn((value, inputRange, outputRange, options) => {
+    const [inMin, inMax] = inputRange;
+    const [outMin, outMax] = outputRange;
+    let progress = (value - inMin) / (inMax - inMin);
+    if (options?.extrapolateLeft === "clamp") {
+      progress = Math.max(0, progress);
+    }
+    if (options?.extrapolateRight === "clamp") {
+      progress = Math.min(1, progress);
+    }
+    return outMin + progress * (outMax - outMin);
+  }),
+  staticFile: vi.fn((path: string) => `/static/${path}`),
+}));
+
+// Mock @remotion/media
+vi.mock("@remotion/media", () => ({
+  Audio: vi.fn(({ src, volume, loop }) => (
+    <audio
+      data-testid="audio"
+      src={src}
+      data-volume={volume}
+      data-loop={loop ? "true" : "false"}
+    />
+  )),
+}));
+/* eslint-enable @remotion/warn-native-media-tag */
+
+describe("PortalAudioManager", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    mockCurrentFrame = 45; // Reset to mid-video frame
+  });
+
+  afterEach(() => {
+    cleanup();
+    vi.resetAllMocks();
+  });
+
+  it("renders without errors", () => {
+    const { container } = render(<PortalAudioManager />);
+    expect(container).toBeInTheDocument();
+  });
+
+  it("renders the background music audio element", () => {
+    const { container } = render(<PortalAudioManager />);
+    const audioElements = container.querySelectorAll('[data-testid="audio"]');
+    expect(audioElements.length).toBe(1);
+  });
+
+  it("uses the correct background music file", () => {
+    const { container } = render(<PortalAudioManager />);
+    const audioElement = container.querySelector('[data-testid="audio"]');
+    expect(audioElement).toBeInTheDocument();
+    expect(audioElement?.getAttribute("src")).toBe(
+      "/static/music/background-music.mp3"
+    );
+  });
+
+  it("sets the background music to loop", () => {
+    const { container } = render(<PortalAudioManager />);
+    const audioElement = container.querySelector('[data-testid="audio"]');
+    expect(audioElement).toBeInTheDocument();
+    expect(audioElement?.getAttribute("data-loop")).toBe("true");
+  });
+});
+
+describe("PortalAudioManager volume behavior", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    mockCurrentFrame = 45;
+  });
+
+  afterEach(() => {
+    cleanup();
+    vi.resetAllMocks();
+  });
+
+  it("renders audio with volume attribute", () => {
+    const { container } = render(<PortalAudioManager />);
+    const audioElement = container.querySelector('[data-testid="audio"]');
+    expect(audioElement).toBeInTheDocument();
+    const volume = audioElement?.getAttribute("data-volume");
+    expect(volume).toBeDefined();
+    expect(parseFloat(volume as string)).toBeGreaterThanOrEqual(0);
+    expect(parseFloat(volume as string)).toBeLessThanOrEqual(1);
+  });
+});
+
+describe("PortalAudioManager fade-in behavior", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  afterEach(() => {
+    cleanup();
+    vi.resetAllMocks();
+  });
+
+  it("starts with zero volume at frame 0", () => {
+    mockCurrentFrame = 0;
+
+    const { container } = render(<PortalAudioManager />);
+    const audioElement = container.querySelector('[data-testid="audio"]');
+    expect(audioElement).toBeInTheDocument();
+    const volume = parseFloat(
+      audioElement?.getAttribute("data-volume") as string
+    );
+    // At frame 0, volume should be 0 (start of fade-in)
+    expect(volume).toBe(0);
+  });
+
+  it("has base volume after fade-in completes", () => {
+    // Frame 45 is after fade-in (1 second = 30 frames)
+    mockCurrentFrame = 45;
+
+    const { container } = render(<PortalAudioManager />);
+    const audioElement = container.querySelector('[data-testid="audio"]');
+    expect(audioElement).toBeInTheDocument();
+    const volume = parseFloat(
+      audioElement?.getAttribute("data-volume") as string
+    );
+    // After fade-in, volume should be at base level (0.25)
+    expect(volume).toBeCloseTo(0.25, 2);
+  });
+
+  it("has partial volume during fade-in", () => {
+    // Frame 15 is midway through fade-in (0.5 seconds into 1 second fade)
+    mockCurrentFrame = 15;
+
+    const { container } = render(<PortalAudioManager />);
+    const audioElement = container.querySelector('[data-testid="audio"]');
+    expect(audioElement).toBeInTheDocument();
+    const volume = parseFloat(
+      audioElement?.getAttribute("data-volume") as string
+    );
+    // Midway through fade-in, volume should be around 0.125 (half of 0.25)
+    expect(volume).toBeCloseTo(0.125, 2);
+  });
+});
+
+describe("PortalAudioManager fade-out behavior", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  afterEach(() => {
+    cleanup();
+    vi.resetAllMocks();
+  });
+
+  it("maintains base volume before fade-out starts", () => {
+    // Frame 2600 is before fade-out (starts at 2700 - 90 = 2610)
+    mockCurrentFrame = 2600;
+
+    const { container } = render(<PortalAudioManager />);
+    const audioElement = container.querySelector('[data-testid="audio"]');
+    expect(audioElement).toBeInTheDocument();
+    const volume = parseFloat(
+      audioElement?.getAttribute("data-volume") as string
+    );
+    // Before fade-out, volume should be at base level (0.25)
+    expect(volume).toBeCloseTo(0.25, 2);
+  });
+
+  it("has reduced volume during fade-out", () => {
+    // Frame 2655 is midway through fade-out (2610 + 45)
+    mockCurrentFrame = 2655;
+
+    const { container } = render(<PortalAudioManager />);
+    const audioElement = container.querySelector('[data-testid="audio"]');
+    expect(audioElement).toBeInTheDocument();
+    const volume = parseFloat(
+      audioElement?.getAttribute("data-volume") as string
+    );
+    // During fade-out, volume should be less than base
+    expect(volume).toBeLessThan(0.25);
+    expect(volume).toBeGreaterThan(0);
+  });
+
+  it("reaches zero volume at the final frame", () => {
+    mockCurrentFrame = 2700;
+
+    const { container } = render(<PortalAudioManager />);
+    const audioElement = container.querySelector('[data-testid="audio"]');
+    expect(audioElement).toBeInTheDocument();
+    const volume = parseFloat(
+      audioElement?.getAttribute("data-volume") as string
+    );
+    // At the last frame, volume should be 0
+    expect(volume).toBe(0);
+  });
+});
+
+describe("PortalAudioManager integration", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    mockCurrentFrame = 45;
+  });
+
+  afterEach(() => {
+    cleanup();
+    vi.resetAllMocks();
+  });
+
+  it("only renders one audio element for background music", () => {
+    const { container } = render(<PortalAudioManager />);
+    const audioElements = container.querySelectorAll('[data-testid="audio"]');
+    expect(audioElements.length).toBe(1);
+  });
+
+  it("does not render any sequence elements (SFX handled by individual scenes)", () => {
+    const { container } = render(<PortalAudioManager />);
+    const sequences = container.querySelectorAll('[data-testid="sequence"]');
+    expect(sequences.length).toBe(0);
+  });
+});

videos/src/components/PortalAudioManager.tsx

@@ -0,0 +1,89 @@
+import { Audio } from "@remotion/media";
+import {
+  staticFile,
+  useVideoConfig,
+  useCurrentFrame,
+  interpolate,
+} from "remotion";
+
+/**
+ * PortalAudioManager Component
+ *
+ * Manages background music for the Portal Presentation video with:
+ * - 1 second fade-in at the beginning
+ * - 3 second fade-out at the end
+ *
+ * Scene-specific sound effects are handled within each scene component
+ * for better maintainability and timing accuracy.
+ *
+ * Scene Structure (90 seconds total @ 30fps = 2700 frames):
+ * 1. Logo Reveal (6s) - Frames 0-180
+ * 2. Portal Title (4s) - Frames 180-300
+ * 3. Dashboard Overview (12s) - Frames 300-660
+ * 4. Meine Meetups (12s) - Frames 660-1020
+ * 5. Top Länder (12s) - Frames 1020-1380
+ * 6. Top Meetups (10s) - Frames 1380-1680
+ * 7. Activity Feed (10s) - Frames 1680-1980
+ * 8. Call to Action (12s) - Frames 1980-2340
+ * 9. Outro (12s) - Frames 2340-2700
+ */
+
+/**
+ * BackgroundMusic - Handles the background music track with fade in/out
+ */
+const BackgroundMusic: React.FC = () => {
+  const frame = useCurrentFrame();
+  const { fps, durationInFrames } = useVideoConfig();
+
+  // Fade-in for 1 second
+  const fadeInDuration = 1 * fps;
+  // Fade-out for 3 seconds
+  const fadeOutDuration = 3 * fps;
+  const fadeOutStart = durationInFrames - fadeOutDuration;
+
+  // Base volume for background music
+  const baseVolume = 0.25;
+
+  // Calculate volume with fade-in and fade-out
+  let volume = baseVolume;
+
+  // Fade-in at the beginning
+  if (frame < fadeInDuration) {
+    volume = interpolate(frame, [0, fadeInDuration], [0, baseVolume], {
+      extrapolateLeft: "clamp",
+      extrapolateRight: "clamp",
+    });
+  }
+  // Fade-out at the end
+  else if (frame >= fadeOutStart) {
+    volume = interpolate(
+      frame,
+      [fadeOutStart, durationInFrames],
+      [baseVolume, 0],
+      {
+        extrapolateLeft: "clamp",
+        extrapolateRight: "clamp",
+      }
+    );
+  }
+
+  return (
+    <Audio src={staticFile("music/background-music.mp3")} volume={volume} loop />
+  );
+};
+
+/**
+ * PortalAudioManager - Main audio manager component for the Portal Presentation
+ *
+ * This component handles the background music with proper fade in/out.
+ * Scene-specific sound effects are embedded within each scene component
+ * for better timing accuracy and maintainability.
+ */
+export const PortalAudioManager: React.FC = () => {
+  return (
+    <>
+      {/* Background Music - plays throughout the entire video */}
+      <BackgroundMusic />
+    </>
+  );
+};