feat: global crossfade curve combo + per-join render/guard plumbing

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

main.py

@@ -4694,6 +4694,12 @@ class MainWindow(QMainWindow):
         self._spn_crossfade.setValue(float(self._settings.value("audio_crossfade", 0.5)))
         self._spn_crossfade.valueChanged.connect(
             lambda v: self._settings.setValue("audio_crossfade", v))
+        self._cmb_curve = QComboBox()
+        for label, name in (("Triangular", "tri"), ("Exponential", "exp"),
+                            ("Logarithmic", "log"), ("Quarter sine", "qsin"),
+                            ("Half sine", "hsin")):
+            self._cmb_curve.addItem(label, name)
+        self._cmb_curve.setToolTip("Crossfade curve at each join")
         self._btn_merge_add_sel = QPushButton("＋ Selection")
         self._btn_merge_add_sel.setToolTip(
             "Add the current audio area (with edits) as a clip")
@@ -5050,6 +5056,8 @@ class MainWindow(QMainWindow):
         xrow = QHBoxLayout()
         xrow.addWidget(QLabel("Crossfade:"))
         xrow.addWidget(self._spn_crossfade)
+        xrow.addWidget(QLabel("Curve:"))
+        xrow.addWidget(self._cmb_curve)
         xrow.addStretch()
         mv.addLayout(xrow)
         brow = QHBoxLayout()
@@ -6749,6 +6757,8 @@ class MainWindow(QMainWindow):
                 item = QListWidgetItem(text)
                 item.setData(Qt.ItemDataRole.UserRole, ap)
                 item.setData(Qt.ItemDataRole.UserRole + 1, dur)
+                item.setData(Qt.ItemDataRole.UserRole + 2, None)   # crossfade override (None = global)
+                item.setData(Qt.ItemDataRole.UserRole + 3, None)   # curve override (None = global)
                 self._merge_list.addItem(item)
         finally:
             QApplication.restoreOverrideCursor()
@@ -6811,22 +6821,33 @@ class MainWindow(QMainWindow):
         return [self._merge_list.item(i).data(Qt.ItemDataRole.UserRole)
                 for i in range(self._merge_list.count())]
 
-    def _merge_guard_ok(self, crossfade: float) -> bool:
-        """False (+ status) if a clip with a KNOWN duration is <= the crossfade
-        (acrossfade needs each clip longer than the crossfade)."""
-        if crossfade <= 0:
-            return True
-        # Clips whose duration couldn't be probed (None) are not flagged here;
-        # if genuinely too short they surface as an ffmpeg error at render.
-        for i in range(self._merge_list.count()):
-            it = self._merge_list.item(i)
-            d = it.data(Qt.ItemDataRole.UserRole + 1)
-            if d is not None and d <= crossfade:
-                name = os.path.basename(it.data(Qt.ItemDataRole.UserRole))
-                self._show_status(
-                    f"'{name}' ({d:.2f}s) is shorter than the "
-                    f"{crossfade:.2f}s crossfade", 6000)
-                return False
+    def _merge_join_values(self) -> tuple[list[float], list[str]]:
+        n = self._merge_list.count()
+        xfs, cvs = [], []
+        for j in range(n - 1):
+            it = self._merge_list.item(j)
+            xo = it.data(Qt.ItemDataRole.UserRole + 2)
+            co = it.data(Qt.ItemDataRole.UserRole + 3)
+            xfs.append(float(xo) if xo is not None else self._spn_crossfade.value())
+            cvs.append(co if co is not None else self._cmb_curve.currentData())
+        return xfs, cvs
+
+    def _merge_guard_ok(self) -> bool:
+        """False (+ status) if a clip with a KNOWN duration is <= its join's
+        crossfade (acrossfade needs both sides longer than the crossfade)."""
+        xfs, _cvs = self._merge_join_values()
+        for j, xf in enumerate(xfs):
+            if xf <= 0:
+                continue
+            for idx in (j, j + 1):
+                it = self._merge_list.item(idx)
+                d = it.data(Qt.ItemDataRole.UserRole + 1)
+                if d is not None and d <= xf:
+                    name = os.path.basename(it.data(Qt.ItemDataRole.UserRole))
+                    self._show_status(
+                        f"'{name}' ({d:.2f}s) is shorter than its "
+                        f"{xf:.2f}s crossfade", 6000)
+                    return False
         return True
 
     def _play_file(self, path: str) -> None:
@@ -6841,8 +6862,9 @@ class MainWindow(QMainWindow):
 
     def _render_merge(self, out_path: str) -> tuple[bool, str]:
         """Render the merge sequence to out_path. Returns (ok, last_stderr_line)."""
-        cmd = build_crossfade_merge_command(
-            self._merge_paths(), self._spn_crossfade.value(), out_path)
+        xfs, cvs = self._merge_join_values()
+        cmd = build_crossfade_merge_command(self._merge_paths(), xfs, out_path,
+                                            curves=cvs)
         QApplication.setOverrideCursor(Qt.CursorShape.WaitCursor)
         err = ""
         try:
@@ -6862,7 +6884,7 @@ class MainWindow(QMainWindow):
         if not paths:
             self._show_status("Add clips to merge first", 3000)
             return
-        if not self._merge_guard_ok(self._spn_crossfade.value()):
+        if not self._merge_guard_ok():
             return
         default_dir = (self._settings.value("audio_extract_dir", "")
                        or os.path.dirname(self._file_path or ""))
@@ -6890,7 +6912,7 @@ class MainWindow(QMainWindow):
         if not paths:
             self._show_status("Add clips to merge first", 3000)
             return
-        if not self._merge_guard_ok(self._spn_crossfade.value()):
+        if not self._merge_guard_ok():
             return
         import tempfile
         fd, tmp = tempfile.mkstemp(suffix=".wav", prefix="8cut_merge_prev_")