feat: add split L/R playback mode for audio sync comparison

sync_audio_test.py

@@ -269,6 +269,7 @@ class SyncWindow(QtWidgets.QMainWindow):
         self.btn_play_a = QtWidgets.QPushButton("Play A")
         self.btn_play_b = QtWidgets.QPushButton("Play B+lag")
         self.btn_play_mix = QtWidgets.QPushButton("Play Mix")
+        self.btn_play_split = QtWidgets.QPushButton("Play L/R")
         self.btn_stop = QtWidgets.QPushButton("Stop")
 
         ctr2.addWidget(QtWidgets.QLabel("Duration:"))
@@ -281,10 +282,10 @@ class SyncWindow(QtWidgets.QMainWindow):
         self.play_dur.setMaximumWidth(80)
         ctr2.addWidget(self.play_dur)
 
-        for b in [self.btn_play_a, self.btn_play_b, self.btn_play_mix, self.btn_stop]:
+        for b in [self.btn_play_a, self.btn_play_b, self.btn_play_mix, self.btn_play_split, self.btn_stop]:
             ctr2.addWidget(b)
         if not HAS_SD:
-            for b in [self.btn_play_a, self.btn_play_b, self.btn_play_mix, self.btn_stop]:
+            for b in [self.btn_play_a, self.btn_play_b, self.btn_play_mix, self.btn_play_split, self.btn_stop]:
                 b.setEnabled(False)
                 b.setToolTip("sounddevice not installed — run make install (optional)")
             ctr2.addWidget(QtWidgets.QLabel("(sounddevice missing — playback disabled)"))
@@ -307,6 +308,7 @@ class SyncWindow(QtWidgets.QMainWindow):
         self.btn_play_a.clicked.connect(lambda: self.play("a"))
         self.btn_play_b.clicked.connect(lambda: self.play("b"))
         self.btn_play_mix.clicked.connect(lambda: self.play("mix"))
+        self.btn_play_split.clicked.connect(lambda: self.play("split"))
         self.btn_stop.clicked.connect(self.stop_play)
 
         self.update_labels()
@@ -513,6 +515,10 @@ class SyncWindow(QtWidgets.QMainWindow):
             elif which == "mix":
                 mix = (a_seg + b_seg) / 2.0
                 sd.play(mix, samplerate=sr)
+            elif which == "split":
+                # A on left, B on right
+                stereo = np.column_stack([a_seg, b_seg])
+                sd.play(stereo, samplerate=sr)
         except Exception as e:
             print(f"playback failed {e}", file=sys.stderr)