diff --git a/src/App.svelte b/src/App.svelte
index 8b29354..9b37c7b 100644
--- a/src/App.svelte
+++ b/src/App.svelte
@@ -262,7 +262,7 @@
       case 'j':
       case 'J':
         e.preventDefault();
-        shuttleRate = adjustShuttle(-1, shuttleRate);
+        shuttleRate = adjustShuttle(-1);
         break;
       case 'k':
       case 'K':
@@ -272,7 +272,7 @@
       case 'l':
       case 'L':
         e.preventDefault();
-        shuttleRate = adjustShuttle(1, shuttleRate);
+        shuttleRate = adjustShuttle(1);
         break;
       case 'Delete':
       case 'Backspace': {
diff --git a/src/lib/transport/playback.ts b/src/lib/transport/playback.ts
index 25a45cd..7894705 100644
--- a/src/lib/transport/playback.ts
+++ b/src/lib/transport/playback.ts
@@ -84,11 +84,12 @@ export function resetShuttleRate() {
   }
 }
 
-export function adjustShuttle(dir: 1 | -1, shuttleRate: number): number {
+export function adjustShuttle(dir: 1 | -1): number {
   const videoEl = getVideo();
-  if (!videoEl) return shuttleRate;
+  if (!videoEl) return 1;
 
-  const nextRate = Math.max(0.25, Math.min(4, shuttleRate + dir * 0.5));
+  const current = videoEl.playbackRate;
+  const nextRate = Math.max(0.25, Math.min(4, current + dir * 0.25));
   videoEl.playbackRate = nextRate;
   if (videoEl.paused) {
     void videoEl.play();
@@ -121,14 +122,13 @@ export function toggleFullscreen(): void {
       console.error('Exit fullscreen failed:', e);
     });
   } else {
-    const videoEl = getVideo();
-    if (!videoEl) return;
-    if (videoEl.requestFullscreen) {
-      videoEl.requestFullscreen().catch((e) => {
+    const el = document.documentElement;
+    if (el.requestFullscreen) {
+      el.requestFullscreen().catch((e) => {
         console.error('Fullscreen request failed:', e);
       });
-    } else if ((videoEl as HTMLVideoElement & { webkitEnterFullscreen?: () => void }).webkitEnterFullscreen) {
-      (videoEl as HTMLVideoElement & { webkitEnterFullscreen: () => void }).webkitEnterFullscreen();
+    } else if ((el as HTMLElement & { webkitRequestFullscreen?: () => void }).webkitRequestFullscreen) {
+      (el as HTMLElement & { webkitRequestFullscreen: () => void }).webkitRequestFullscreen();
     }
   }
 }
diff --git a/tests/lib/transport/playback.test.ts b/tests/lib/transport/playback.test.ts
index 7436cc0..f1145ee 100644
--- a/tests/lib/transport/playback.test.ts
+++ b/tests/lib/transport/playback.test.ts
@@ -19,6 +19,7 @@ import {
   isFullscreenActive,
   setPlaybackRate,
   getPlaybackRate,
+  adjustShuttle,
 } from '$lib/transport/playback';
 
 function createMockVideoElement(): HTMLVideoElement {
@@ -85,9 +86,11 @@ describe('playback — fullscreen helpers', () => {
     expect(isFullscreenActive()).toBe(false);
   });
 
-  it('toggleFullscreen calls requestFullscreen when not fullscreen', () => {
+  it('toggleFullscreen calls requestFullscreen on document.documentElement', () => {
+    const spy = vi.fn().mockResolvedValue(undefined);
+    document.documentElement.requestFullscreen = spy;
     toggleFullscreen();
-    expect(mockVideo.requestFullscreen).toHaveBeenCalled();
+    expect(spy).toHaveBeenCalled();
   });
 
   it('isFullscreenActive returns true when fullscreen element exists', () => {
@@ -127,3 +130,59 @@ describe('playback — playback rate helpers', () => {
     expect(getPlaybackRate()).toBe(1);
   });
 });
+
+describe('playback — adjustShuttle', () => {
+  let mockVideo: HTMLVideoElement;
+
+  beforeEach(() => {
+    mockVideo = createMockVideoElement();
+    setVideoElement(mockVideo);
+    mockVideo.playbackRate = 1;
+    Object.defineProperty(mockVideo, 'paused', {
+      value: true,
+      writable: true,
+      configurable: true,
+    });
+    mockVideo.play = vi.fn().mockResolvedValue(undefined);
+  });
+
+  it('increases rate by 0.25 when dir is 1', () => {
+    const result = adjustShuttle(1);
+    expect(result).toBe(1.25);
+    expect(mockVideo.playbackRate).toBe(1.25);
+  });
+
+  it('decreases rate by 0.25 when dir is -1', () => {
+    const result = adjustShuttle(-1);
+    expect(result).toBe(0.75);
+    expect(mockVideo.playbackRate).toBe(0.75);
+  });
+
+  it('reads current rate from video element, not external state', () => {
+    mockVideo.playbackRate = 0.75;
+    const result = adjustShuttle(1);
+    expect(result).toBe(1);
+  });
+
+  it('clamps to minimum 0.25', () => {
+    mockVideo.playbackRate = 0.25;
+    const result = adjustShuttle(-1);
+    expect(result).toBe(0.25);
+  });
+
+  it('clamps to maximum 4', () => {
+    mockVideo.playbackRate = 4;
+    const result = adjustShuttle(1);
+    expect(result).toBe(4);
+  });
+
+  it('starts playback if paused', () => {
+    adjustShuttle(1);
+    expect(mockVideo.play).toHaveBeenCalled();
+  });
+
+  it('returns 1 when no video element', () => {
+    setVideoElement(null);
+    expect(adjustShuttle(1)).toBe(1);
+  });
+});