Smooth realtime display frame pacing

scripts/test_gui_contracts.mjs

@@ -3,6 +3,7 @@ import assert from 'node:assert/strict';
 
 const html = fs.readFileSync(new URL('../www/index.html', import.meta.url), 'utf8');
 const main = fs.readFileSync(new URL('../www/main.js', import.meta.url), 'utf8');
+const audio = fs.readFileSync(new URL('../www/core/audio.js', import.meta.url), 'utf8');
 
 const styleSelect = html.match(/<select\b[^>]*\bid="styleSel"[^>]*>/)?.[0] || '';
 assert(styleSelect, 'style selector is missing');
@@ -16,5 +17,11 @@ assert(/renderRequestGeneration\s*\+=\s*1/.test(main),
   'render requests must carry a generation that survives asynchronous rendering');
 assert(/renderRequestGeneration\s*===\s*renderGeneration\)\s*renderDirty\s*=\s*false/.test(main),
   'an in-flight render must not clear a newer render request');
+assert(/const frameDue\s*=\s*audioOk\s*\|\|\s*elapsed\s*>=\s*target/.test(main),
+  'live displays must use requestAnimationFrame directly instead of a second 60 Hz gate');
+assert(/await updateActiveMeters\(env, d, CONFIG\);\s*[^]*?env\.requestRender\?\.\('audio'\)/.test(audio),
+  'audio rendering must be requested after active meters finish updating');
+assert(!/phoenixPacketRaf\s*=\s*requestAnimationFrame/.test(audio),
+  'metrics packets must not wait for a competing requestAnimationFrame pump');
 
 console.log('GUI contract regression tests passed');

www/core/audio.js

@@ -26,7 +26,6 @@ let lifecycleHandlersBound = false;
 let recoverTimer = null;
 let lastHardRecoverAt = 0;
 let pendingPhoenixFrame = null;
-let phoenixPacketRaf = 0;
 let phoenixPacketBusy = false;
 
 const RMS_RING = { L: new Float32Array(512), R: new Float32Array(512), i: 0, n: 0 };
@@ -125,8 +124,6 @@ function closePhoenixSocket() {
   if (phoenixVisualsRaf) cancelAnimationFrame(phoenixVisualsRaf);
   phoenixVisualsRaf = 0;
   pendingPhoenixFrame = null;
-  if (phoenixPacketRaf) cancelAnimationFrame(phoenixPacketRaf);
-  phoenixPacketRaf = 0;
   phoenixPacketBusy = false;
 }
 
@@ -432,7 +429,6 @@ async function applyIncomingAudioPacket(env, packet, CONFIG, sampleTs = performa
   const previousSeq = Number(env.audio.phoenixMetricsSeq || 0);
   if (Number.isFinite(seq) && seq > 0 && previousSeq > 0 && seq <= previousSeq) return;
   if (Number.isFinite(seq) && seq > 0) env.audio.phoenixMetricsSeq = seq;
-  env.requestRender?.('audio');
   env.audio.lastSampleTs = sampleTs;
   env.audio.alive = true;
   if (Number.isFinite(Number(d.sampleRate)) && Number(d.sampleRate) > 0) {
@@ -487,6 +483,10 @@ async function applyIncomingAudioPacket(env, packet, CONFIG, sampleTs = performa
   }
 
   await updateActiveMeters(env, d, CONFIG);
+  // Publish the frame only after every active meter has consumed the packet.
+  // Otherwise the canvas loop can draw between the data update and the meter
+  // update, producing an old frame followed by a visible catch-up step.
+  env.requestRender?.('audio');
 }
 
 function buildPhoenixMeterPacket(frame) {
@@ -627,23 +627,26 @@ function mergePendingPhoenixFrame(previous, next) {
 }
 
 function schedulePhoenixPacketPump(env, CONFIG) {
-  if (phoenixPacketRaf || phoenixPacketBusy || !pendingPhoenixFrame) return;
-  phoenixPacketRaf = requestAnimationFrame(async () => {
-    phoenixPacketRaf = 0;
-    const frame = pendingPhoenixFrame;
-    pendingPhoenixFrame = null;
-    if (!frame) return;
-    phoenixPacketBusy = true;
+  if (phoenixPacketBusy || !pendingPhoenixFrame) return;
+  phoenixPacketBusy = true;
+  void (async () => {
     try {
-      const packet = buildPhoenixMeterPacket(frame);
-      await applyIncomingAudioPacket(env, packet, CONFIG, performance.now());
+      // Consume the newest packet immediately. Incoming packets are still
+      // coalesced while an asynchronous meter/config update is in progress,
+      // but they no longer wait for a second requestAnimationFrame loop.
+      while (pendingPhoenixFrame) {
+        const frame = pendingPhoenixFrame;
+        pendingPhoenixFrame = null;
+        const packet = buildPhoenixMeterPacket(frame);
+        await applyIncomingAudioPacket(env, packet, CONFIG, performance.now());
+      }
     } catch (err) {
       console.warn('Phoenix packet error:', err);
     } finally {
       phoenixPacketBusy = false;
       if (pendingPhoenixFrame) schedulePhoenixPacketPump(env, CONFIG);
     }
-  });
+  })();
 }
 
 function enqueuePhoenixFrame(env, CONFIG, frame) {

www/main.js

@@ -2698,14 +2698,20 @@ async function loop(now){
   const currentAudioSeq = Math.max(currentMetricsSeq, currentVisualsSeq, currentXySeq);
   const audioDirty = currentAudioSeq > lastRenderedAudioSeq;
   const shouldRenderFrame =
+    audioOk ||
     renderDirty ||
     audioDirty ||
     !audioOk ||
     style === 'options-panel' ||
     style === 'recorder' ||
     renderStyle === 'clock';
-  if (elapsed >= target){
-    lastFrameTime = now - (elapsed % targetMs);
+  // With live audio, requestAnimationFrame itself is the display clock. An
+  // additional exact 60 Hz comparison occasionally rejected a real 60 Hz
+  // frame because of fractional timestamp jitter, creating 33 ms pauses in
+  // otherwise smooth peak decay. Only throttle the disconnected state.
+  const frameDue = audioOk || elapsed >= target;
+  if (frameDue){
+    lastFrameTime = audioOk ? now : now - (elapsed % targetMs);
     try{
       updateRect();
       meterHitRects.length = 0;