fix: crash AudioWorklet khi output mono - xử lý mọi số channel trong fluidsynth-bridge + ép stereo outputChannelCount=2

app/static/js/services/soundfontPlayer.js

@@ -141,7 +141,15 @@
 
                     if (!_useScriptNode) {
                         try {
-                            _workletNode = new AudioWorkletNode(_audioCtx, 'fluidsynth-bridge');
+                            // Force stereo output regardless of the device's
+                            // channel count — FluidSynth renders stereo, and a
+                            // mono output would crash the worklet (out[1] undefined).
+                            _workletNode = new AudioWorkletNode(_audioCtx, 'fluidsynth-bridge', {
+                                numberOfOutputs: 1,
+                                outputChannelCount: [2],
+                                channelCount: 2,
+                                channelCountMode: 'explicit'
+                            });
                             _workletNode.connect(_gainNode);
                             console.log("[SonicSF] AudioWorklet node connected via gain");
                             _startRenderLoop();

app/static/js/worklets/fluidsynth-bridge.js

@@ -15,17 +15,24 @@ class FluidSynthBridge extends AudioWorkletProcessor {
 
   process(inputs, outputs) {
     const out = outputs[0];
-    if (!out) return true;
+    if (!out || out.length === 0) return true;
     this.called++;
+    const numCh = out.length;
     const len = out[0].length;
     const qL = this.leftQ;
     const qR = this.rightQ;
     let fi = 0;
     let si = 0;
+    // Handle any output channel count (mono devices produce 1 channel, so
+    // out[1] may be undefined — never write into a missing channel).
     for (let i = 0; i < len; i++) {
-      if (fi >= qL.length) { out[0][i] = 0; out[1][i] = 0; continue; }
-      out[0][i] = qL[fi][si];
-      out[1][i] = qR[fi][si];
+      if (fi >= qL.length) {
+        for (let c = 0; c < numCh; c++) out[c][i] = 0;
+        continue;
+      }
+      for (let c = 0; c < numCh; c++) {
+        out[c][i] = c % 2 === 0 ? qL[fi][si] : qR[fi][si];
+      }
       si++;
       if (si >= qL[fi].length) { fi++; si = 0; }
     }