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/stream/server.go

@@ -1,6 +1,7 @@
 package stream
 
 import (
+	"bufio"
 	"context"
 	"crypto/rand"
 	"encoding/hex"
@@ -15,6 +16,7 @@ import (
 	"time"
 
 	"github.com/gin-gonic/gin"
+	"github.com/nareix/joy4/av"
 	"github.com/nareix/joy4/av/avutil"
 	"github.com/nareix/joy4/av/pubsub"
 	"github.com/nareix/joy4/format"
@@ -82,6 +84,23 @@ func (w writeFlusher) Flush() error {
 	return nil
 }
 
+type bufferedWriteFlusher struct {
+	bufw        *bufio.Writer
+	httpFlusher http.Flusher
+}
+
+func (w *bufferedWriteFlusher) Write(p []byte) (n int, err error) {
+	return w.bufw.Write(p)
+}
+
+func (w *bufferedWriteFlusher) Flush() error {
+	if err := w.bufw.Flush(); err != nil {
+		return err
+	}
+	w.httpFlusher.Flush()
+	return nil
+}
+
 // NewRTMPServer creates and initializes a new media server
 func NewRTMPServer() *RTMPServer {
 	s := &RTMPServer{
@@ -235,13 +254,47 @@ func (s *RTMPServer) HandleHTTPFLV(c *gin.Context) {
 	c.Status(http.StatusOK)
 	flusher.Flush()
 
-	muxer := flv.NewMuxerWriteFlusher(writeFlusher{
+	// Coalesce the 3 internal write calls of WriteTag using a 4KB bufio.Writer
+	bufWriter := bufio.NewWriterSize(c.Writer, 4096)
+	bwf := &bufferedWriteFlusher{
+		bufw:        bufWriter,
 		httpFlusher: flusher,
-		Writer:      c.Writer,
-	})
+	}
+
+	muxer := flv.NewMuxerWriteFlusher(bwf)
 	cursor := q.Latest()
 
-	if err := avutil.CopyFile(muxer, cursor); err != nil && err != io.EOF {
+	// Write header first
+	streams, err := cursor.Streams()
+	if err != nil {
+		monitor.Errorf("HTTP-FLV failed to get cursor streams: %v", err)
+		return
+	}
+	if err = muxer.WriteHeader(streams); err != nil {
+		monitor.Errorf("HTTP-FLV failed to write header: %v", err)
+		return
+	}
+	if err = bwf.Flush(); err != nil {
+		return
+	}
+
+	// Read and write packet loop with per-packet flushing for low latency
+	for {
+		var pkt av.Packet
+		pkt, err = cursor.ReadPacket()
+		if err != nil {
+			break
+		}
+		if err = muxer.WritePacket(pkt); err != nil {
+			break
+		}
+		// Flush immediately so the frame is sent to the client (grouped write syscall)
+		if err = bwf.Flush(); err != nil {
+			break
+		}
+	}
+
+	if err != nil && err != io.EOF {
 		errStr := err.Error()
 		if strings.Contains(errStr, "broken pipe") || strings.Contains(errStr, "connection reset by peer") {
 			monitor.Infof("HTTP-FLV viewer disconnected: %s", streamPath)
@@ -299,10 +352,11 @@ func (s *RTMPServer) startVariantTranscoders(roomID string) {
 			"ffmpeg",
 			"-nostdin",
 			"-loglevel", "error",
+			"-fflags", "nobuffer",
 			"-i", inputURL,
 			"-vf", "scale="+profile.scale+":force_original_aspect_ratio=decrease",
 			"-c:v", "libx264",
-			"-preset", "veryfast",
+			"-preset", "ultrafast",
 			"-tune", "zerolatency",
 			"-g", "48",
 			"-keyint_min", "48",