fix(egress): single composite fanning out to all destinations

apps/web/src/app/api/stream/egress/start/route.test.ts

@@ -61,9 +61,7 @@ beforeEach(() => {
   process.env.SUPABASE_SERVICE_ROLE_KEY = 'service-key';
   mockGetAuthenticatedUser.mockResolvedValue({ user: mockUser, error: null });
   mockSingle.mockResolvedValue({ data: hostSession, error: null });
-  mockStartRoomCompositeEgress
-    .mockResolvedValueOnce({ egressId: 'eg-yt' })
-    .mockResolvedValueOnce({ egressId: 'eg-tw' });
+  mockStartRoomCompositeEgress.mockResolvedValue({ egressId: 'eg-combined' });
 });
 
 describe('POST /api/stream/egress/start', () => {
@@ -91,32 +89,26 @@ describe('POST /api/stream/egress/start', () => {
     expect(res.status).toBe(403);
   });
 
-  it('starts one isolated egress per destination', async () => {
+  it('starts a single composite fanning out to all destinations', async () => {
     const urls = ['rtmp://a.rtmp.youtube.com/live2/yt-key', 'rtmp://live.twitch.tv/app/tw-key'];
     const res = await POST(createRequest({ sessionId, rtmpUrls: urls }));
 
     expect(res.status).toBe(200);
     const json = (await res.json()) as { data: { egressId: string; egressIds: string[] } };
-    expect(json.data.egressIds).toEqual(['eg-yt', 'eg-tw']);
-    expect(json.data.egressId).toBe('eg-yt');
+    expect(json.data.egressIds).toEqual(['eg-combined']);
+    expect(json.data.egressId).toBe('eg-combined');
 
-    // One egress per URL — each StreamOutput carries a single destination.
-    expect(mockStartRoomCompositeEgress).toHaveBeenCalledTimes(2);
-    expect(mockStartRoomCompositeEgress).toHaveBeenNthCalledWith(
-      1,
+    // One composite (one Chrome render + one H264 encode) carrying every URL in
+    // a single StreamOutput — half the CPU of one-egress-per-destination.
+    expect(mockStartRoomCompositeEgress).toHaveBeenCalledTimes(1);
+    expect(mockStartRoomCompositeEgress).toHaveBeenCalledWith(
       `session-${sessionId}`,
-      expect.objectContaining({ stream: expect.objectContaining({ urls: [urls[0]] }) }),
+      expect.objectContaining({ stream: expect.objectContaining({ urls }) }),
       expect.objectContaining({
         layout: 'speaker',
         // 1s keyframe interval so YouTube Live leaves "Preparing" reliably
         encodingOptions: expect.objectContaining({ keyFrameInterval: 1, height: 1080 }),
       })
     );
-    expect(mockStartRoomCompositeEgress).toHaveBeenNthCalledWith(
-      2,
-      `session-${sessionId}`,
-      expect.objectContaining({ stream: expect.objectContaining({ urls: [urls[1]] }) }),
-      expect.objectContaining({ layout: 'speaker' })
-    );
   });
 });

apps/web/src/app/api/stream/egress/start/route.ts

@@ -92,24 +92,24 @@ export async function POST(request: Request) {
       keyFrameInterval: 1,
     });
 
-    // One egress per destination instead of a single combined pipeline. With a
-    // shared RoomComposite fanning out to YouTube + Twitch in one StreamOutput,
-    // a stall on one sink (e.g. YouTube stuck on "Preparing") can back-pressure
-    // the shared flvmux/encoder and degrade or stall the others. Independent
-    // egresses isolate each platform and give each its own egressId/status.
-    const results = await Promise.all(
-      rtmpUrls.map((url) =>
-        egress.startRoomCompositeEgress(
-          roomName,
-          { stream: new StreamOutput({ protocol: StreamProtocol.RTMP, urls: [url] }) },
-          { layout: 'speaker', encodingOptions }
-        )
-      )
+    // A SINGLE RoomComposite that fans out to every destination in one
+    // StreamOutput. One composite = one headless Chrome rendering + one H264
+    // encode, regardless of how many platforms; each extra RTMP URL is just
+    // another cheap mux/push. Running one isolated egress *per destination*
+    // (the previous approach) duplicated the whole render+encode pipeline, so
+    // streaming to two platforms needed ~2x the CPU and the 4-vCPU SFU droplet
+    // thrashed — the second composite (e.g. YouTube) starved and stuck on
+    // "Preparing", and the CPU spike broke the host's publisher DTLS handshake
+    // ("could not establish pc connection"). keyFrameInterval:1 (above) already
+    // mitigates the YouTube-stall back-pressure that motivated the split.
+    const info = await egress.startRoomCompositeEgress(
+      roomName,
+      { stream: new StreamOutput({ protocol: StreamProtocol.RTMP, urls: rtmpUrls }) },
+      { layout: 'speaker', encodingOptions }
     );
-    const egressIds = results.map((info) => info.egressId);
 
-    // egressId (first) kept for backward compatibility with older clients.
-    return successResponse({ egressIds, egressId: egressIds[0] });
+    // egressIds[] kept for clients that track the full set; egressId for older ones.
+    return successResponse({ egressIds: [info.egressId], egressId: info.egressId });
   } catch (error) {
     return handleApiError(error);
   }