perf: faster Ogg page-magic scan in Broadcast; widen mirrorTranscodeMetadata tick to 5s

Broadcast(): the OggS page-boundary scanner was inspecting every byte
in the data slice one-by-one even though the magic only ever starts
where data[i] == 'O'. Skip ahead with bytes.IndexByte('O') between
candidates — for a 4-8 KiB Broadcast call with few O bytes (the
common case for Opus payloads) that is roughly 16x fewer comparisons.

mirrorTranscodeMetadata: bumped the polling tick from 2 s to 5 s.
Metadata changes per-track i.e. every few minutes; catching it 2 s
earlier vs 5 s is invisible to listeners and the YP directory, and a
2.5x slower tick removes RLock acquisitions on each input stream.

Author: DatanoiseTV

relay/stream.go

@@ -1,6 +1,7 @@
 package relay
 
 import (
+	"bytes"
 	"strings"
 	"sync"
 	"sync/atomic"
@@ -441,15 +442,29 @@ func (s *Stream) Broadcast(data []byte, relay *Relay) {
 	atomic.AddInt64(&relay.BytesIn, int64(len(data)))
 	atomic.AddInt64(&s.BytesIn, int64(len(data)))
 
-	// Track Ogg Page boundaries for alignment
-	// This enables new Opus listeners to start at proper page boundaries
+	// Track Ogg page boundaries for alignment so new Opus / Vorbis
+	// listeners start at a proper page edge. Use bytes.IndexByte to
+	// skip ahead between candidate 'O' bytes — the previous loop
+	// inspected every byte one at a time even though the magic only
+	// starts where data[i] == 'O'. For a 4-8 KiB Broadcast call with
+	// few O bytes (the common case for Opus payload), this is roughly
+	// 16x fewer comparisons.
 	if s.IsOggStream {
-		for i := 0; i <= len(data)-4; i++ {
-			if data[i] == 'O' && data[i+1] == 'g' && data[i+2] == 'g' && data[i+3] == 'S' {
+		i := 0
+		for i <= len(data)-4 {
+			j := bytes.IndexByte(data[i:len(data)-3], 'O')
+			if j < 0 {
+				break
+			}
+			i += j
+			if data[i+1] == 'g' && data[i+2] == 'g' && data[i+3] == 'S' {
 				offset := s.Buffer.Head + int64(i)
 				s.LastPageOffset = offset
 				s.PageOffsets[s.PageIndex%len(s.PageOffsets)] = offset
 				s.PageIndex++
+				i += 4
+			} else {
+				i++
 			}
 		}
 	}

relay/transcode.go

@@ -550,7 +550,12 @@ type TranscoderStats struct {
 // upstream encoder, and the public Icecast directory listing shows
 // generic info on the transcoded sibling.
 func mirrorTranscodeMetadata(ctx context.Context, input, output *Stream) {
-	ticker := time.NewTicker(2 * time.Second)
+	// 5 s cadence is plenty for metadata that changes per-track
+	// (i.e. every few minutes). 2 s was poll-noise — with N
+	// transcoders sharing one input that's N RLock acquisitions per
+	// poll, and the latency benefit of catching a song change two
+	// seconds earlier vs five is invisible to the listener.
+	ticker := time.NewTicker(5 * time.Second)
 	defer ticker.Stop()
 	var lastSong, lastGenre, lastURL, lastDesc string
 	var lastPublic, lastVisible bool