From 687c050c28325d48a2199dcdb9f3d4cd6c679348 Mon Sep 17 00:00:00 2001
From: DCCONSTRUCTIONS <dcconstructions@MacBook-Pro-DCCONSTRUCTIONS-2.local>
Date: Sun, 23 Aug 2026 12:47:54 +0300
Subject: [PATCH] =?UTF-8?q?=D0=A3=D1=81=D1=82=D1=80=D0=B0=D0=BD=D0=B5?=
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---
 .../src/components/MseFmp4WebSocketPlayer.tsx |  7 +++++--
 .../test/observationSources.test.mjs          | 19 +++++++++++++++++++
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/apps/control-station/src/components/MseFmp4WebSocketPlayer.tsx b/apps/control-station/src/components/MseFmp4WebSocketPlayer.tsx
index b9865b0..374a8cc 100644
--- a/apps/control-station/src/components/MseFmp4WebSocketPlayer.tsx
+++ b/apps/control-station/src/components/MseFmp4WebSocketPlayer.tsx
@@ -470,8 +470,6 @@ export function MseFmp4WebSocketPlayer({
       : "Подключение к локальному видеопотоку");
     const mediaSource = new MediaSource();
     objectUrl = URL.createObjectURL(mediaSource);
-    video.src = objectUrl;
-    startupWatchdog?.armFirstMedia();
 
     const onSourceOpen = () => {
       if (!transportIsCurrent() || failed) return;
@@ -562,7 +560,12 @@ export function MseFmp4WebSocketPlayer({
       });
     };
 
+    // Register before assigning the object URL. `video.src` is the action that
+    // lets the browser open this MediaSource; a fast sequential MSE lease must
+    // not fire `sourceopen` in the gap before its only listener exists.
     mediaSource.addEventListener("sourceopen", onSourceOpen, { once: true });
+    startupWatchdog?.armFirstMedia();
+    video.src = objectUrl;
 
     const disposeTransport = () => {
       if (disposed) return;
diff --git a/apps/control-station/test/observationSources.test.mjs b/apps/control-station/test/observationSources.test.mjs
index a9cc814..c0f334a 100644
--- a/apps/control-station/test/observationSources.test.mjs
+++ b/apps/control-station/test/observationSources.test.mjs
@@ -1,4 +1,5 @@
 import assert from "node:assert/strict";
+import { readFile } from "node:fs/promises";
 import { after, before, test } from "node:test";
 
 import { createElement } from "react";
@@ -184,6 +185,24 @@ test("floating observation interaction captures resize and movable header pointe
   );
 });
 
+test("live camera registers sourceopen before assigning the MSE object URL", async () => {
+  const source = await readFile(
+    new URL("../src/components/MseFmp4WebSocketPlayer.tsx", import.meta.url),
+    "utf8",
+  );
+  const listenerIndex = source.indexOf(
+    'mediaSource.addEventListener("sourceopen", onSourceOpen, { once: true });',
+  );
+  const sourceAssignmentIndex = source.indexOf("video.src = objectUrl;");
+
+  assert.ok(listenerIndex >= 0, "sourceopen listener must remain explicit");
+  assert.ok(sourceAssignmentIndex >= 0, "MediaSource object URL assignment must remain explicit");
+  assert.ok(
+    listenerIndex < sourceAssignmentIndex,
+    "sourceopen listener must exist before video.src can open the MediaSource",
+  );
+});
+
 test("recorded observation timeline clamps relative seek time without epoch precision in the UI", () => {
   const range = normalizeTimelineRange({
     min: 0,