replay capture ?

server/src/services/roomCameraSnapshotService.js

@@ -3,9 +3,11 @@ const logger = require('../globals/logger').child('roomCameraSnapshot');
 const { getRoomCameras, roomCameraEvents } = require('./roomCameraService');
 
 const POLL_INTERVAL_MS = 800;
+const REPLAY_FRAME_COUNT = 15;
 const FETCH_TIMEOUT_MS = 2000;
 
 const cameraState = new Map(); // id -> {frame, ts, error, failures, fetching}
+const frameHistory = new Map(); // id -> [{buffer, ts}]
 const events = new EventEmitter(); // frame, status
 let pollTimer = null;
 
@@ -16,6 +18,15 @@ function markState(id, updates = {}) {
   return next;
 }
 
+function recordFrame(id, buffer, ts) {
+  const history = frameHistory.get(id) || [];
+  history.push({ buffer, ts });
+  if (history.length > REPLAY_FRAME_COUNT) {
+    history.splice(0, history.length - REPLAY_FRAME_COUNT);
+  }
+  frameHistory.set(id, history);
+}
+
 async function fetchSnapshot(camera) {
   const { id, url } = camera;
   const state = cameraState.get(id);
@@ -32,6 +43,7 @@ async function fetchSnapshot(camera) {
     const buffer = Buffer.from(arrayBuffer);
     const ts = Date.now();
     markState(id, { frame: buffer, ts, error: null, failures: 0 });
+    recordFrame(id, buffer, ts);
     events.emit('frame', { id, buffer, ts });
   } catch (err) {
     const failures = (state?.failures || 0) + 1;
@@ -50,6 +62,7 @@ function stopAll() {
     pollTimer = null;
   }
   cameraState.clear();
+  frameHistory.clear();
 }
 
 function startAll() {
@@ -71,6 +84,20 @@ function getState(id) {
   };
 }
 
+function getReplayFrames(id, count = REPLAY_FRAME_COUNT) {
+  const history = frameHistory.get(id) || [];
+  if (!history.length) return [];
+  return history.slice(Math.max(0, history.length - count));
+}
+
+function getReplayFrameDelayMs() {
+  return POLL_INTERVAL_MS;
+}
+
+function getReplayFrameCount() {
+  return REPLAY_FRAME_COUNT;
+}
+
 roomCameraEvents.on('update', () => {
   logger.info('Room cameras changed; restarting snapshot pollers');
   startAll();
@@ -81,4 +108,7 @@ startAll();
 module.exports = {
   roomCameraStreamEvents: events,
   getRoomCameraState: getState,
+  getRoomCameraFrames: getReplayFrames,
+  getRoomCameraReplayDelayMs: getReplayFrameDelayMs,
+  getRoomCameraReplayFrameCount: getReplayFrameCount,
 };