Initial commit: SyncWatch Chrome extension + WebSocket server

extension/content.js

@@ -0,0 +1,66 @@
+let applyingRemote = false;
+
+function getMediaElement() {
+  const els = Array.from(document.querySelectorAll('video, audio'));
+  if (!els.length) return null;
+  const playing = els.find((el) => !el.paused && !el.ended);
+  if (playing) return playing;
+  const videos = els.filter((el) => el.tagName === 'VIDEO');
+  return videos.length ? videos[0] : els[0];
+}
+
+function onPlay(e) {
+  if (applyingRemote) return;
+  chrome.runtime.sendMessage({ type: 'media_event', action: 'play', time: e.target.currentTime });
+}
+
+function onPause(e) {
+  if (applyingRemote) return;
+  chrome.runtime.sendMessage({ type: 'media_event', action: 'pause', time: e.target.currentTime });
+}
+
+function onSeeked(e) {
+  if (applyingRemote) return;
+  chrome.runtime.sendMessage({ type: 'media_event', action: 'seek', time: e.target.currentTime });
+}
+
+function attachToMedia(el) {
+  if (el._syncwatchAttached) return;
+  el._syncwatchAttached = true;
+  el.addEventListener('play', onPlay);
+  el.addEventListener('pause', onPause);
+  el.addEventListener('seeked', onSeeked);
+}
+
+function attachAll() {
+  document.querySelectorAll('video, audio').forEach(attachToMedia);
+}
+
+attachAll();
+
+const observer = new MutationObserver(attachAll);
+observer.observe(document.documentElement, { childList: true, subtree: true });
+
+chrome.runtime.onMessage.addListener((msg) => {
+  if (msg.type !== 'apply_sync') return;
+
+  const el = getMediaElement();
+  if (!el) return;
+
+  applyingRemote = true;
+
+  // Re-sync time on any action; only seek if drift is significant
+  const drift = Math.abs(el.currentTime - msg.time);
+
+  if (msg.action === 'play') {
+    if (drift > 1) el.currentTime = msg.time;
+    el.play().catch(() => {});
+  } else if (msg.action === 'pause') {
+    el.pause();
+    if (drift > 1) el.currentTime = msg.time;
+  } else if (msg.action === 'seek') {
+    el.currentTime = msg.time;
+  }
+
+  setTimeout(() => { applyingRemote = false; }, 500);
+});