diff --git a/packages/sandbox/app/shared/sources.ts b/packages/sandbox/app/shared/sources.ts
index 669e28ff..ac1eaead 100644
--- a/packages/sandbox/app/shared/sources.ts
+++ b/packages/sandbox/app/shared/sources.ts
@@ -1,6 +1,4 @@
-export type SourceId = 'hls-1' | 'hls-2' | 'hls-3' | 'hls-4' | 'hls-5' | 'mp4-1';
-
-export const SOURCES: Record<SourceId, { label: string; url: string; type: 'hls' | 'mp4'; subType?: 'mp4' | 'ts' }> = {
+export const SOURCES = {
   'hls-1': {
     label: 'HLS - Big Buck Bunny',
     url: 'https://stream.mux.com/VcmKA6aqzIzlg3MayLJDnbF55kX00mds028Z65QxvBYaA.m3u8',
@@ -36,7 +34,9 @@ export const SOURCES: Record<SourceId, { label: string; url: string; type: 'hls'
     url: 'https://stream.mux.com/lhnU49l1VGi3zrTAZhDm9LUUxSjpaPW9BL4jY25Kwo4/highest.mp4',
     type: 'mp4',
   },
-};
+} as const;
+
+export type SourceId = keyof typeof SOURCES;
 
 export const SOURCE_IDS = Object.keys(SOURCES) as SourceId[];
 export const MP4_SOURCE_IDS = SOURCE_IDS.filter((id) => SOURCES[id].type === 'mp4');
diff --git a/packages/spf/src/dom/features/segment-loader-actor.ts b/packages/spf/src/dom/features/segment-loader-actor.ts
index 339e7ba7..767e5dbf 100644
--- a/packages/spf/src/dom/features/segment-loader-actor.ts
+++ b/packages/spf/src/dom/features/segment-loader-actor.ts
@@ -162,7 +162,12 @@ export function createSegmentLoaderActor(
 
     // Case 2: Init
     if (actorCtx.initTrackId !== track.id) {
-      tasks.push({ type: 'append-init', meta: { trackId: track.id }, url: track.initialization.url });
+      tasks.push({
+        type: 'append-init',
+        meta: { trackId: track.id },
+        url: track.initialization.url,
+        ...(track.initialization.byteRange !== undefined && { byteRange: track.initialization.byteRange }),
+      });
     }
 
     // Case 3: Segments
@@ -190,6 +195,7 @@ export function createSegmentLoaderActor(
             trackBandwidth: track.bandwidth,
           },
           url: segment.url,
+          ...(segment.byteRange !== undefined && { byteRange: segment.byteRange }),
         });
       }
     }
diff --git a/packages/spf/src/dom/features/tests/load-segments.test.ts b/packages/spf/src/dom/features/tests/load-segments.test.ts
index 0946a1ae..578f4582 100644
--- a/packages/spf/src/dom/features/tests/load-segments.test.ts
+++ b/packages/spf/src/dom/features/tests/load-segments.test.ts
@@ -902,6 +902,134 @@ describe('loadSegments forward buffer flushing', () => {
   });
 });
 
+// ---------------------------------------------------------------------------
+// Byte-range segment fetching (fMP4 / CMAF range-request streams)
+// ---------------------------------------------------------------------------
+
+describe('loadSegments byte-range segment fetching', () => {
+  it('sends Range headers for byte-range init and media segments', async () => {
+    const segments: Segment[] = [
+      {
+        id: 's0',
+        url: 'http://example.com/video.mp4',
+        startTime: 0,
+        duration: 6,
+        byteRange: { start: 1000, end: 2999 },
+      },
+      {
+        id: 's1',
+        url: 'http://example.com/video.mp4',
+        startTime: 6,
+        duration: 6,
+        byteRange: { start: 3000, end: 4999 },
+      },
+    ];
+
+    const rangeHeaders: string[] = [];
+    globalThis.fetch = vi.fn().mockImplementation((input: RequestInfo | URL) => {
+      const range = (input as Request).headers?.get('Range');
+      if (range) rangeHeaders.push(range);
+      return Promise.resolve(new Response(new ArrayBuffer(100)));
+    });
+
+    const { loadSegments } = await import('../load-segments');
+    const { createState: cs } = await import('../../../core/state/create-state');
+
+    const track = {
+      type: 'video' as const,
+      id: 'track-1',
+      url: 'http://example.com/video.m3u8',
+      mimeType: 'video/mp4',
+      codecs: ['avc1.42E01E'],
+      bandwidth: 1_000_000,
+      initialization: { url: 'http://example.com/video.mp4', byteRange: { start: 0, end: 999 } },
+      segments,
+      startTime: 0,
+      duration: 12,
+    };
+
+    const state = cs<SegmentLoadingState>({
+      preload: 'auto',
+      selectedVideoTrackId: 'track-1',
+      currentTime: 0,
+      presentation: {
+        id: 'p1',
+        url: 'http://example.com/playlist.m3u8',
+        startTime: 0,
+        duration: 12,
+        selectionSets: [{ id: 'ss1', type: 'video', switchingSets: [{ id: 'sw1', type: 'video', tracks: [track] }] }],
+      },
+    });
+
+    const { sourceBuffer, actor } = makeSourceBufferWithActor();
+    const owners = cs<SegmentLoadingOwners>({ videoBuffer: sourceBuffer, videoBufferActor: actor });
+
+    const cleanup = loadSegments({ state, owners }, { type: 'video' });
+
+    await vi.waitFor(
+      () => {
+        expect(owners.current.videoBufferActor?.snapshot.context.segments).toHaveLength(2);
+      },
+      { timeout: 3000 }
+    );
+
+    expect(rangeHeaders).toContain('bytes=0-999'); // init segment
+    expect(rangeHeaders).toContain('bytes=1000-2999'); // s0
+    expect(rangeHeaders).toContain('bytes=3000-4999'); // s1
+
+    cleanup();
+  });
+
+  it('does not send Range header for non-byte-range segments', async () => {
+    const segments = [makeSegment('s0', 0, 10)];
+
+    const rangeHeaders: string[] = [];
+    globalThis.fetch = vi.fn().mockImplementation((input: RequestInfo | URL) => {
+      const range = (input as Request).headers?.get('Range');
+      if (range) rangeHeaders.push(range);
+      return Promise.resolve(new Response(new ArrayBuffer(100)));
+    });
+
+    const { loadSegments } = await import('../load-segments');
+    const { createState: cs } = await import('../../../core/state/create-state');
+
+    const state = cs<SegmentLoadingState>({
+      preload: 'auto',
+      selectedVideoTrackId: 'track-1',
+      currentTime: 0,
+      presentation: {
+        id: 'p1',
+        url: 'http://example.com/playlist.m3u8',
+        startTime: 0,
+        duration: 10,
+        selectionSets: [
+          {
+            id: 'ss1',
+            type: 'video',
+            switchingSets: [{ id: 'sw1', type: 'video', tracks: [makeResolvedVideoTrack(segments)] }],
+          },
+        ],
+      },
+    });
+
+    const { sourceBuffer, actor } = makeSourceBufferWithActor();
+    const owners = cs<SegmentLoadingOwners>({ videoBuffer: sourceBuffer, videoBufferActor: actor });
+
+    const cleanup = loadSegments({ state, owners }, { type: 'video' });
+
+    await vi.waitFor(
+      () => {
+        expect(owners.current.videoBufferActor?.snapshot.context.segments).toHaveLength(1);
+      },
+      { timeout: 3000 }
+    );
+
+    expect(rangeHeaders).toHaveLength(0);
+
+    cleanup();
+  });
+});
+
 // ---------------------------------------------------------------------------
 // Streaming bandwidth tracking
 // ---------------------------------------------------------------------------