feat: merge save + preview (crossfade render, duration guard, ffplay preview)

main.py

@@ -37,6 +37,7 @@ from core.paths import _bin, _log, build_export_path, build_sequence_dir, format
 from core.ffmpeg import (
     _RATIOS, resolve_keyframe, apply_keyframes_to_jobs,
     build_ffmpeg_command, build_audio_extract_command, build_audio_clip_command,
+    build_crossfade_merge_command,
     audio_edit_filters, probe_duration, detect_hw_encoders,
 )
 from core.db import ProcessedDB
@@ -6649,11 +6650,101 @@ class MainWindow(QMainWindow):
         if row >= 0:
             self._merge_list.takeItem(row)
 
-    def _on_merge_preview(self) -> None:
+    def _merge_paths(self) -> list[str]:
-        pass   # implemented in M4
+        from PyQt6.QtCore import Qt
+        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)."""
+        from PyQt6.QtCore import Qt
+        if crossfade <= 0:
+            return True
+        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
+        return True
+
+    def _play_file(self, path: str) -> None:
+        """Start ffplay audition on an existing file (stops any current one)."""
+        from PyQt6.QtCore import QProcess
+        self._stop_audition()
+        self._audition_proc = QProcess(self)
+        self._audition_proc.finished.connect(self._on_audition_finished)
+        self._audition_proc.errorOccurred.connect(self._on_audition_error)
+        self._audition_proc.start(
+            _bin("ffplay"), ["-autoexit", "-nodisp", "-loglevel", "error", path])
+
+    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)
+        QApplication.setOverrideCursor(Qt.CursorShape.WaitCursor)
+        err = ""
+        try:
+            proc = subprocess.run(cmd, capture_output=True, text=True, timeout=300)
+        except Exception as e:
+            proc = None; err = str(e)
+        finally:
+            QApplication.restoreOverrideCursor()
+        if proc is not None and proc.returncode == 0 and os.path.exists(out_path):
+            return True, ""
+        err = (proc.stderr.strip().splitlines()[-1] if proc and proc.stderr
+               else (err if proc is None else "ffmpeg failed"))
+        return False, err
 
     def _on_merge_save(self) -> None:
-        pass   # implemented in M4
+        paths = self._merge_paths()
+        if not paths:
+            self._show_status("Add clips to merge first", 3000)
+            return
+        if not self._merge_guard_ok(self._spn_crossfade.value()):
+            return
+        default_dir = (self._settings.value("audio_extract_dir", "")
+                       or os.path.dirname(self._file_path or ""))
+        out, _sel = QFileDialog.getSaveFileName(
+            self, "Save merged audio", os.path.join(default_dir, "merged.wav"),
+            "WAV (*.wav);;MP3 (*.mp3);;FLAC (*.flac);;All files (*)")
+        if not out:
+            return
+        if not os.path.splitext(out)[1]:
+            out += ".wav"
+        os.makedirs(os.path.dirname(out) or ".", exist_ok=True)
+        self._show_status("Merging…")
+        ok, err = self._render_merge(out)
+        if ok:
+            self._settings.setValue("audio_extract_dir", os.path.dirname(out))
+            actual = probe_duration(out)
+            self._show_status(
+                f"Saved merged: {os.path.basename(out)} ({(actual or 0):.2f}s)", 5000)
+        else:
+            self._show_status("Merge failed", 5000)
+            QMessageBox.warning(self, "Merge failed", f"Could not merge:\n\n{err}")
+
+    def _on_merge_preview(self) -> None:
+        paths = self._merge_paths()
+        if not paths:
+            self._show_status("Add clips to merge first", 3000)
+            return
+        if not self._merge_guard_ok(self._spn_crossfade.value()):
+            return
+        import tempfile
+        fd, tmp = tempfile.mkstemp(suffix=".wav", prefix="8cut_merge_prev_")
+        os.close(fd)
+        self._merge_temps.add(tmp)
+        self._show_status("Rendering preview…")
+        ok, err = self._render_merge(tmp)
+        if ok:
+            self._play_file(tmp)
+        else:
+            self._show_status(f"Preview failed: {err}" if err else "Preview render failed", 5000)
 
     def _on_wave_refresh(self) -> None:
         """Decode the current audio area and repaint the waveform strip."""
@@ -6694,7 +6785,6 @@ class MainWindow(QMainWindow):
             self._btn_audio_play.setChecked(False)
             return
         import tempfile
-        from PyQt6.QtCore import QProcess
         start = self._cursor
         dur = self._spn_audio_len.value()
         edit_filters = self._current_edit_filters()
@@ -6713,11 +6803,7 @@ class MainWindow(QMainWindow):
             self._btn_audio_play.setChecked(False)
             self._show_status("Audition render failed", 3000)
             return
-        self._audition_proc = QProcess(self)
+        self._play_file(tmp)
-        self._audition_proc.finished.connect(self._on_audition_finished)
-        self._audition_proc.errorOccurred.connect(self._on_audition_error)
-        self._audition_proc.start(
-            _bin("ffplay"), ["-autoexit", "-nodisp", "-loglevel", "error", tmp])
         self._btn_audio_play.setText("■ Stop")
 
     def _on_audition_error(self, _err) -> None:

tests/test_ui_structure.py

@@ -459,3 +459,70 @@ def test_merge_add_stores_duration_role(win, tmp_path):
     win._merge_add_paths([str(a)])
     # empty fixture -> ffprobe fails -> duration is None; M4 must tolerate None
     assert win._merge_list.item(0).data(Qt.ItemDataRole.UserRole + 1) is None
+
+
+def test_merge_save_builds_command(win, tmp_path, monkeypatch):
+    import main as m, pytest
+    from PyQt6.QtCore import Qt
+    a = tmp_path / "a.wav"; b = tmp_path / "b.wav"; a.write_bytes(b""); b.write_bytes(b"")
+    win._merge_list.clear()
+    win._merge_add_paths([str(a), str(b)])
+    win._merge_list.item(0).setData(Qt.ItemDataRole.UserRole + 1, 5.0)   # long enough
+    win._merge_list.item(1).setData(Qt.ItemDataRole.UserRole + 1, 5.0)
+    win._spn_crossfade.setValue(0.75)
+    seen = {}
+    class _Stop(Exception): pass
+    def fake(clips, xf, out):
+        seen.update(clips=clips, xf=xf, out=out); raise _Stop
+    monkeypatch.setattr(m, "build_crossfade_merge_command", fake)
+    monkeypatch.setattr(m.QFileDialog, "getSaveFileName",
+                        staticmethod(lambda *a, **k: (str(tmp_path / "m.wav"), "")))
+    with pytest.raises(_Stop):
+        win._on_merge_save()
+    assert seen["clips"] == [str(a), str(b)]
+    assert seen["xf"] == 0.75
+    assert seen["out"].endswith(".wav")
+
+
+def test_merge_save_blocks_short_clip(win, tmp_path, monkeypatch):
+    import main as m
+    from PyQt6.QtCore import Qt
+    a = tmp_path / "a.wav"; b = tmp_path / "b.wav"; a.write_bytes(b""); b.write_bytes(b"")
+    win._merge_list.clear()
+    win._merge_add_paths([str(a), str(b)])
+    win._merge_list.item(0).setData(Qt.ItemDataRole.UserRole + 1, 0.1)   # shorter than crossfade
+    win._merge_list.item(1).setData(Qt.ItemDataRole.UserRole + 1, 5.0)
+    win._spn_crossfade.setValue(0.5)
+    calls = {"n": 0}
+    monkeypatch.setattr(m, "build_crossfade_merge_command",
+                        lambda *a, **k: calls.__setitem__("n", calls["n"] + 1) or [])
+    monkeypatch.setattr(m.QFileDialog, "getSaveFileName",
+                        staticmethod(lambda *a, **k: (_ for _ in ()).throw(AssertionError("dialog opened"))))
+    win._on_merge_save()            # guard must block before dialog/builder
+    assert calls["n"] == 0
+
+
+def test_merge_save_empty_is_noop(win):
+    win._merge_list.clear()
+    win._on_merge_save()           # no raise, no dialog
+
+
+def test_merge_preview_blocks_short_clip(win, tmp_path, monkeypatch):
+    import main as m
+    from PyQt6.QtCore import Qt
+    a = tmp_path / "a.wav"; b = tmp_path / "b.wav"; a.write_bytes(b""); b.write_bytes(b"")
+    win._merge_list.clear()
+    win._merge_add_paths([str(a), str(b)])
+    win._merge_list.item(0).setData(Qt.ItemDataRole.UserRole + 1, 0.1)
+    win._merge_list.item(1).setData(Qt.ItemDataRole.UserRole + 1, 5.0)
+    win._spn_crossfade.setValue(0.5)
+    calls = {"n": 0}
+    monkeypatch.setattr(m, "build_crossfade_merge_command",
+                        lambda *a, **k: calls.__setitem__("n", calls["n"] + 1) or [])
+    win._on_merge_preview()
+    assert calls["n"] == 0
+
+
+def test_merge_preview_empty_is_noop(win):
+    win._merge_list.clear()
+    win._on_merge_preview()