feat: implement multiprocessing for transcription with immediate cancellation

app.py

@@ -4,7 +4,8 @@ import tkinter as tk
 from tkinter import ttk
 from tkinter import filedialog
 from tkinter import messagebox
-from src._LocalTranscribe import transcribe, get_path, detect_backend
+from src._LocalTranscribe import transcribe, get_path, detect_backend, _transcribe_worker_process
+import multiprocessing as mp
 import customtkinter
 import threading
 
@@ -220,8 +221,10 @@ class App:
         self.timestamps_switch.pack(side=tk.LEFT, padx=5)
         # Progress Bar
         self.progress_bar = ttk.Progressbar(master, length=200, mode='indeterminate')
-        # Stop event for cancellation
-        self._stop_event = threading.Event()
+        # Worker process handle (replaces thread+stop_event for true immediate cancellation)
+        self._proc = None
+        self._parent_conn = None
+        self._child_conn = None
         # Button actions frame
         button_frame = customtkinter.CTkFrame(master)
         button_frame.pack(fill=tk.BOTH, padx=10, pady=10)
@@ -262,9 +265,28 @@ class App:
         print("─" * 46)
     # Helper functions
     def _stop_transcription(self):
-        self._stop_event.set()
         self.stop_button.configure(state=tk.DISABLED)
-        print("⛔  Stop requested — finishing current file…")
+        if self._proc and self._proc.is_alive():
+            self._proc.terminate()
+            try:
+                self._proc.join(timeout=3)
+            except Exception:
+                pass
+            if self._proc.is_alive():
+                self._proc.kill()
+                try:
+                    self._proc.join(timeout=1)
+                except Exception:
+                    pass
+        # Close pipe ends — no semaphores, so no leak
+        for conn in (self._parent_conn, self._child_conn):
+            try:
+                if conn:
+                    conn.close()
+            except Exception:
+                pass
+        self._parent_conn = self._child_conn = None
+        print("⛔  Transcription stopped by user.")
 
     def _model_desc_text(self, model_name):
         info = MODEL_INFO.get(model_name)
@@ -287,49 +309,67 @@ class App:
         self.path_entry.insert(0, folder_path)
     # Start transcription
     def start_transcription(self):
-        self._stop_event.clear()
-        self.transcribe_button.configure(state=tk.DISABLED)
-        self.stop_button.configure(state=tk.NORMAL)
-        threading.Thread(target=self.transcribe_thread, daemon=True).start()
-    # Threading
-    def transcribe_thread(self):
-        path = self.path_entry.get()
         model_display = self.model_combobox.get()
-        # Ignore the visual separator
         if model_display.startswith('─'):
             messagebox.showinfo("Invalid selection", "Please select a model, not the separator line.")
-            self.transcribe_button.configure(state=tk.NORMAL)
             return
+        self.transcribe_button.configure(state=tk.DISABLED)
+        self.stop_button.configure(state=tk.NORMAL)
+        path = self.path_entry.get()
         model = HF_MODEL_MAP.get(model_display, model_display)
         lang_label = self.language_combobox.get()
         language = WHISPER_LANGUAGES.get(lang_label, lang_label) if lang_label else None
-        verbose = True   # always show transcription progress in the console panel
         timestamps = self.timestamps_var.get()
-        # Show progress bar
+        glob_file = get_path(path)
         self.progress_bar.pack(fill=tk.X, padx=5, pady=5)
         self.progress_bar.start()
-        # Setting path and files
-        glob_file = get_path(path)
-        #messagebox.showinfo("Message", "Starting transcription!")
-        # Start transcription
+        self._parent_conn, self._child_conn = mp.Pipe(duplex=False)
+        self._proc = mp.Process(
+            target=_transcribe_worker_process,
+            args=(self._child_conn, path, glob_file, model, language, True, timestamps),
+            daemon=True,
+        )
+        self._proc.start()
+        self._child_conn.close()  # parent doesn't write; close its write-end
+        self._child_conn = None
+        self.master.after(100, self._poll_worker)
+
+    def _poll_worker(self):
+        done = False
+        result = None
         try:
-            output_text = transcribe(path, glob_file, model, language, verbose, timestamps, stop_event=self._stop_event)
-        except UnboundLocalError:
-            messagebox.showinfo("Files not found error!", 'Nothing found, choose another folder.')
+            while self._parent_conn and self._parent_conn.poll():
+                msg = self._parent_conn.recv()
+                if isinstance(msg, tuple) and msg[0] == '__done__':
+                    done = True
+                    result = msg[1]
+                else:
+                    sys.stdout.write(msg)
+                    sys.stdout.flush()
+        except EOFError:
+            # Child closed the pipe (normal completion or kill)
+            done = True
+        except Exception:
             pass
-        except ValueError as e:
-            messagebox.showinfo("Error", str(e))
-        # Hide progress bar
+        if done or (self._proc and not self._proc.is_alive()):
+            if self._parent_conn:
+                try:
+                    self._parent_conn.close()
+                except Exception:
+                    pass
+                self._parent_conn = None
+            self._on_transcription_done(result)
+        else:
+            self.master.after(100, self._poll_worker)
+
+    def _on_transcription_done(self, output_text):
         self.progress_bar.stop()
         self.progress_bar.pack_forget()
-        # Restore buttons
         self.stop_button.configure(state=tk.DISABLED)
         self.transcribe_button.configure(state=tk.NORMAL)
-        # Recover output text
-        try:
-            messagebox.showinfo("Finished!", output_text)
-        except UnboundLocalError:
-            pass
+        if output_text:
+            title = "Finished!" if not output_text.startswith('⚠') else "Error"
+            messagebox.showinfo(title, output_text)
 
 if __name__ == "__main__":
     # Setting custom themes

src/_LocalTranscribe.py

@@ -424,3 +424,43 @@ def transcribe(path, glob_file, model=None, language=None, verbose=False, timest
     print(output_text)
     print(SEP)
     return output_text
+
+
+def _transcribe_worker_process(conn, path, glob_file, model, language, verbose, timestamps):
+    """Child-process entry point for the UI's multiprocessing backend.
+
+    Redirects stdout/stderr → pipe connection so the main process can display
+    output in the console panel.  The main process sends SIGTERM/SIGKILL to
+    stop this process immediately, including any in-progress download or inference.
+    """
+    import sys
+
+    class _PipeWriter:
+        def __init__(self, c):
+            self.c = c
+
+        def write(self, text):
+            if text:
+                try:
+                    self.c.send(text)
+                except Exception:
+                    pass
+
+        def flush(self):
+            pass
+
+    writer = _PipeWriter(conn)
+    sys.stdout = writer
+    sys.stderr = writer
+
+    result = '⚠  No output produced.'
+    try:
+        result = transcribe(path, glob_file, model, language, verbose, timestamps)
+    except Exception as exc:
+        result = f'⚠  Unexpected error: {exc}'
+    finally:
+        try:
+            conn.send(('__done__', result))
+        except Exception:
+            pass
+        conn.close()