cancel in-flight ffmpeg when stop is called during preparation

frigate/debug_replay.py

@@ -272,6 +272,9 @@ class DebugReplayManager:
         except Exception as exc:
             logger.exception("Debug replay startup failed")
             with self._lock:
+                # If stop() already ran while we were preparing, don't overwrite idle state.
+                if self._state == ReplayState.idle:
+                    return
                 self._set_state(ReplayState.error, error_message=str(exc))
                 # Drop session pointers so the next /start is allowed.
                 self.replay_camera_name = None
@@ -355,23 +358,33 @@ class DebugReplayManager:
             return
 
         replay_name = self.replay_camera_name
+        was_preparing = self._state == ReplayState.preparing_clip
 
-        # Publish remove event so subscribers stop and remove from their config
+        if was_preparing and self._active_process is not None:
-        if replay_name in frigate_config.cameras:
+            logger.info("Cancelling in-flight replay clip generation")
+            try:
+                self._active_process.terminate()
+            except Exception as exc:
+                logger.warning("Failed to terminate ffmpeg subprocess: %s", exc)
+
+        # Keep a reference so we can join the worker after we've finished cleanup.
+        worker = self._worker_thread
+
+        # Only publish the remove event if the camera was actually published.
+        if (
+            not was_preparing
+            and replay_name is not None
+            and replay_name in frigate_config.cameras
+        ):
             config_publisher.publish_update(
                 CameraConfigUpdateTopic(CameraConfigUpdateEnum.remove, replay_name),
                 frigate_config.cameras[replay_name],
             )
-            # Do NOT pop here — let subscribers handle removal from the shared
-            # config dict when they process the ZMQ message to avoid race conditions
 
-        # Defensive DB cleanup
+        if replay_name is not None:
-        self._cleanup_db(replay_name)
+            self._cleanup_db(replay_name)
+            self._cleanup_files(replay_name)
 
-        # Remove filesystem artifacts
-        self._cleanup_files(replay_name)
-
-        # Reset state
         self.replay_camera_name = None
         self.source_camera = None
         self.clip_path = None
@@ -381,6 +394,10 @@ class DebugReplayManager:
 
         logger.info("Debug replay stopped and cleaned up: %s", replay_name)
 
+        # Bounded worker join so the API never hangs.
+        if worker is not None and worker.is_alive():
+            worker.join(timeout=2.0)
+
     def _build_camera_config_dict(
         self,
         source_config,

frigate/test/test_debug_replay.py

@@ -198,3 +198,55 @@ class TestDebugReplayManagerAsyncStart(unittest.TestCase):
             self.assertEqual(self.manager.state, ReplayState.error)
             self.assertIsNotNone(self.manager.error_message)
             self.assertIn("ffmpeg", self.manager.error_message.lower())
+
+
+class TestDebugReplayManagerCancellation(unittest.TestCase):
+    def test_stop_during_preparing_clip_terminates_ffmpeg(self):
+        manager = DebugReplayManager()
+        frigate_config = MagicMock()
+        frigate_config.cameras = {"front": MagicMock()}
+        frigate_config.ffmpeg.ffmpeg_path = "/bin/sh"
+        publisher = MagicMock()
+
+        recordings_qs = MagicMock()
+        recordings_qs.count.return_value = 1
+        recordings_qs.__iter__.return_value = iter([MagicMock(path="/tmp/r1.mp4")])
+
+        terminated_event = threading.Event()
+        fake_proc = MagicMock()
+        original_terminate = MagicMock(side_effect=lambda: terminated_event.set())
+        fake_proc.terminate = original_terminate
+
+        def fake_helper(cmd, *, expected_duration_seconds, on_progress, process_started, **kwargs):
+            if process_started is not None:
+                process_started(fake_proc)
+            # Block until stop() calls fake_proc.terminate()
+            terminated_event.wait(timeout=5)
+            return -15, "killed"
+
+        with (
+            patch.object(manager, "_query_recordings", return_value=recordings_qs),
+            patch("frigate.debug_replay.run_ffmpeg_with_progress", side_effect=fake_helper),
+            patch("os.path.exists", return_value=True),
+            patch("os.makedirs"),
+            patch("os.remove"),
+            patch("builtins.open", unittest.mock.mock_open()),
+        ):
+            manager.start(
+                source_camera="front",
+                start_ts=100.0,
+                end_ts=200.0,
+                frigate_config=frigate_config,
+                config_publisher=publisher,
+            )
+            # Wait for the worker to register the active process
+            for _ in range(50):
+                if manager._active_process is fake_proc:
+                    break
+                time.sleep(0.02)
+            self.assertEqual(manager.state, ReplayState.preparing_clip)
+
+            manager.stop(frigate_config=frigate_config, config_publisher=publisher)
+
+            self.assertTrue(original_terminate.called, "terminate() should have been called")
+            self.assertEqual(manager.state, ReplayState.idle)