perf: 优化后端性能与直播延迟，包含数据库WAL模式、流媒体写缓冲、转码 Preset 优化、聊天锁和指标采集优化，以及前端自动追帧功能

backend/internal/chat/hub.go

@@ -66,20 +66,25 @@ func (h *Hub) Run() {
 			}
 			h.rooms[client.RoomID][client] = true
 
-			// Send existing history to the newly joined client
+			// Copy existing history to send outside the lock
+			var historyCopy []Message
 			if history, ok := h.roomsHistory[client.RoomID]; ok {
-				for _, msg := range history {
-					msg.IsHistory = true
-					msgBytes, _ := json.Marshal(msg)
-					// Use select to avoid blocking if client's send channel is full
+				historyCopy = make([]Message, len(history))
+				copy(historyCopy, history)
+			}
+			h.mutex.Unlock()
+
+			// Send history outside the lock
+			for _, msg := range historyCopy {
+				msg.IsHistory = true
+				msgBytes, err := json.Marshal(msg)
+				if err == nil {
 					select {
 					case client.Send <- msgBytes:
 					default:
-						// If send fails, we could potentially log or ignore
 					}
 				}
 			}
-			h.mutex.Unlock()
 
 		case client := <-h.unregister:
 			h.mutex.Lock()
@@ -99,6 +104,12 @@ func (h *Hub) Run() {
 			h.mutex.Unlock()
 
 		case message := <-h.broadcast:
+			// Marshal message outside the lock to optimize performance
+			msgBytes, err := json.Marshal(message)
+			if err != nil {
+				continue
+			}
+
 			h.mutex.Lock()
 			// Only store "chat" and "danmaku" messages in history
 			if message.Type == "chat" || message.Type == "danmaku" {
@@ -111,7 +122,6 @@ func (h *Hub) Run() {
 
 			clients := h.rooms[message.RoomID]
 			if clients != nil {
-				msgBytes, _ := json.Marshal(message)
 				for client := range clients {
 					select {
 					case client.Send <- msgBytes: