perf: switch to Low-Latency HLS for ~1-3s live stream latency

Previously mediamtx used standard MPEG-TS HLS (2s segments, 3-segment
playlist window) and hls.js was configured with lowLatencyMode:false.
The default liveSyncDurationCount:3 and liveMaxLatencyDurationCount:10
allowed 20+ second drift before catch-up triggered.

Changes:
- mediamtx: hlsVariant lowLatency — generates 200ms parts inside 2s
  segments; LL-HLS clients receive each part as it completes instead of
  waiting for the full segment. hlsSegmentCount raised to 7 for playlist
  compatibility with non-LL-HLS clients.
- hls.js: lowLatencyMode:true enables part fetching and blocking playlist
  requests (_HLS_msn/_HLS_part); maxBufferLength:4 prevents buffering far
  ahead; liveSyncDurationCount:1 / liveMaxLatencyDurationCount:3 keep the
  player within ~2-4s of the live edge.
- Express schedule gate: endsWith('.m3u8') → includes('.m3u8') so blocking
  playlist requests (index.m3u8?_HLS_msn=N&_HLS_part=N) are also gated.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/src/components/VideoPlayer.tsx

@@ -51,7 +51,14 @@ export default function VideoPlayer({ src, onOffline }: Props) {
     };
 
     if (Hls.isSupported()) {
-      const hls = new Hls({ enableWorker: true, lowLatencyMode: false });
+      const hls = new Hls({
+        enableWorker: true,
+        lowLatencyMode: true,   // use LL-HLS parts + blocking playlist requests
+        backBufferLength: 30,   // keep 30s of playback history (seeking)
+        maxBufferLength: 4,     // don't buffer more than 4s ahead of playback
+        liveSyncDurationCount: 1,       // target 1 segment from the live edge
+        liveMaxLatencyDurationCount: 3, // catch up if drift exceeds 3 segments
+      });
       hlsRef.current = hls;
 
       hls.loadSource(src);

mediamtx-hwaccel.yml

@@ -28,9 +28,10 @@ rtspAddress: 127.0.0.1:8554
 hls: yes
 hlsAddress: :8888
 hlsAlwaysRemux: yes
-hlsVariant: mpegts
+hlsVariant: lowLatency
+hlsSegmentCount: 7
 hlsSegmentDuration: 2s
-hlsSegmentCount: 3
+hlsPartDuration: 200ms
 hlsAllowOrigins: ['*']
 
 # Authenticate every publish action via Express

mediamtx.yml

@@ -22,9 +22,10 @@ srtAddress: :7000
 hls: yes
 hlsAddress: :8888
 hlsAlwaysRemux: yes
-hlsVariant: mpegts
+hlsVariant: lowLatency
+hlsSegmentCount: 7
 hlsSegmentDuration: 2s
-hlsSegmentCount: 3
+hlsPartDuration: 200ms
 hlsAllowOrigins: ['*']
 
 # Authenticate every publish action via Express

server/src/index.ts

@@ -67,7 +67,7 @@ async function main() {
     // the early-start window (host connected, but scheduled window not open yet).
     // Only check .m3u8 playlist requests — segment requests are already gated
     // by the playlist not being delivered.
-    if (streamKey && req.url.endsWith('.m3u8')) {
+    if (streamKey && req.url.includes('.m3u8')) {
       try {
         const stream = await getStreamByKey(streamKey);
         if (stream && !await isWithinSchedule(stream.id)) {