keep predicted target box positive and add regression tests

A shrinking object's predicted size could reach zero, so the relative zoom ratio divided by zero and sent a NaN zoom to the camera. The predicted size is now floored at 1 px. Tests also cover the movement time intercept and the pan/tilt timestamps that absolute zoom overwrites.

frigate/ptz/autotrack.py

@@ -609,7 +609,7 @@ class PtzAutoTracker(threading.Thread):
         predicted_size = max(
             right - left + frames * (velocity[2] - velocity[0]),
             bottom - top + frames * (velocity[3] - velocity[1]),
-            0,
+            1,
         )
 
         # target_box is the squared size raised to the zoom factor

frigate/test/test_ptz_autotrack.py

@@ -11,13 +11,14 @@ KeyError on the autotracker thread or silently keep the wrong state:
   running its motion estimator for a camera that could not autotrack.
 """
 
+import asyncio
 import unittest
-from unittest.mock import MagicMock
+from unittest.mock import AsyncMock, MagicMock
 
 import numpy as np
 
 from frigate.camera import PTZMetrics
-from frigate.config import FrigateConfig
+from frigate.config import FrigateConfig, ZoomingModeEnum
 from frigate.config.camera.updater import CameraConfigUpdateEnum
 from frigate.ptz.autotrack import PtzAutoTracker, calculate_max_target_box
 
@@ -126,6 +127,20 @@ class TestAutotrackerDisable(unittest.TestCase):
 
 
 class TestAutotrackerPrediction(unittest.TestCase):
+    def test_movement_time_uses_the_fitted_intercept_unchanged(self) -> None:
+        tracker = _make_tracker()
+        tracker.intercept = {CAMERA: 0.5}
+        tracker.move_coefficients = {CAMERA: [0.3, 0.8]}
+
+        self.assertAlmostEqual(tracker._predict_movement_time(CAMERA, 0.25, 0.25), 0.7)
+
+    def test_shrinking_box_keeps_a_positive_target_box(self) -> None:
+        # 60 px shrinking 6 px/frame reaches zero after 2 s at 5 fps
+        target_box = self._target_box_for((0, 0, 60, 60), [3, 3, -3, -3], 2.0)
+
+        self.assertGreater(target_box, 0)
+        self.assertTrue(np.isfinite(target_box))
+
     def test_approaching_object_keeps_its_velocity(self) -> None:
         # the box grows, so the corners move in opposite directions
         tracker = _make_tracker()
@@ -148,8 +163,16 @@ class TestAutotrackerPrediction(unittest.TestCase):
         self.assertFalse(np.any(velocity))
 
     def _target_box(self, velocity: list[float], predicted_time: float) -> float:
+        return self._target_box_for((900, 400, 1000, 600), velocity, predicted_time)
+
+    def _target_box_for(
+        self,
+        box: tuple[int, int, int, int],
+        velocity: list[float],
+        predicted_time: float,
+    ) -> float:
         tracker = _make_tracker()
-        tracker.tracked_object_history = {CAMERA: [{"box": (900, 400, 1000, 600)}]}
+        tracker.tracked_object_history = {CAMERA: [{"box": box}]}
         tracker.tracked_object_metrics = {
             CAMERA: {"target_box": 0.2, "velocity": np.array(velocity)}
         }
@@ -170,6 +193,51 @@ class TestAutotrackerPrediction(unittest.TestCase):
         self.assertEqual(self._target_box([-1, -2, 1, 2], 0), 0.2)
 
 
+class TestAutotrackerMoveQueue(unittest.IsolatedAsyncioTestCase):
+    async def test_absolute_zoom_does_not_overwrite_the_pan_tilt_sample(self) -> None:
+        tracker = _make_tracker()
+        autotracking = tracker.config.cameras[CAMERA].onvif.autotracking
+        autotracking.zooming = ZoomingModeEnum.absolute
+        autotracking.calibrate_on_startup = True
+        metrics = tracker.ptz_metrics[CAMERA]
+
+        tracker.stop_event = MagicMock()
+        tracker.stop_event.is_set.side_effect = [False, True]
+        tracker.move_queues = {CAMERA: asyncio.Queue()}
+        tracker.move_queue_locks = {CAMERA: asyncio.Lock()}
+        tracker.intercept = {CAMERA: 0.5}
+        tracker.move_metrics = {CAMERA: []}
+        tracker._wait_until_stopped = AsyncMock()
+        tracker._calculate_move_coefficients = MagicMock()
+
+        async def move_relative(*_args) -> None:
+            metrics.start_time.value = 100.0
+            metrics.stop_time.value = 102.0
+
+        async def zoom_absolute(*_args) -> None:
+            metrics.start_time.value = 103.0
+            metrics.stop_time.value = 0
+
+        tracker.onvif._move_relative = AsyncMock(side_effect=move_relative)
+        tracker.onvif._zoom_absolute = AsyncMock(side_effect=zoom_absolute)
+
+        tracker.move_queues[CAMERA].put_nowait((50.0, 0.5, 0.5, 0.5))
+        await tracker._process_move_queue(CAMERA)
+
+        tracker.onvif._zoom_absolute.assert_awaited_once()
+        self.assertEqual(
+            tracker.move_metrics[CAMERA],
+            [
+                {
+                    "pan": 0.5,
+                    "tilt": 0.5,
+                    "start_timestamp": 100.0,
+                    "end_timestamp": 102.0,
+                }
+            ],
+        )
+
+
 class TestMaxTargetBox(unittest.TestCase):
     def test_follows_zoom_factor(self) -> None:
         self.assertAlmostEqual(calculate_max_target_box(0.5), 0.6**2)