feat: Add video playback functionality and inference support

- Introduced VideoPlayer class to handle local video playback, emitting frames via frame_ready signal.
- Updated MainWindow to switch between camera and video sources, integrating video playback controls.
- Enhanced AppMenuBar with options to open video files and manage inference models.
- Implemented BboxOverlay for displaying detection results on video frames.
- Added InferenceManager to manage YOLO inference in a separate process, with error handling and restart logic.
- Created tests for BboxOverlay and InferenceManager to ensure functionality and robustness.
- Updated pyproject.toml to include optional dependencies for inference support.

tests/test_bbox_overlay.py

@@ -0,0 +1,180 @@
+"""Tests for BboxOverlay — coordinate mapping and state management."""
+
+from __future__ import annotations
+
+from unittest.mock import MagicMock
+
+import pytest
+from PySide6.QtCore import QRect, QSize
+
+from app.inference.bbox_overlay import BboxOverlay, Detection
+
+
+class TestDetection:
+    def test_namedtuple_fields(self) -> None:
+        d = Detection(x1=10.0, y1=20.0, x2=100.0, y2=200.0, conf=0.87, label="label")
+        assert d.x1 == 10.0
+        assert d.label == "label"
+        assert d.conf == pytest.approx(0.87)
+
+    def test_immutable(self) -> None:
+        d = Detection(0, 0, 1, 1, 0.5, "x")
+        with pytest.raises(AttributeError):
+            d.conf = 0.9  # type: ignore[misc]
+
+
+class TestBboxOverlayState:
+    def setup_method(self) -> None:
+        self.overlay = BboxOverlay()
+
+    def test_initially_no_detections(self) -> None:
+        assert self.overlay._detections == []
+
+    def test_initially_source_size_empty(self) -> None:
+        assert self.overlay._source_size.isEmpty()
+
+    def test_on_detections_stores_data(self) -> None:
+        dets = [Detection(0, 0, 100, 100, 0.9, "label")]
+        self.overlay.on_detections(dets, (640, 480))
+        assert self.overlay._detections == dets
+        assert self.overlay._source_size == QSize(640, 480)
+
+    def test_clear_removes_detections(self) -> None:
+        self.overlay.on_detections([Detection(0, 0, 10, 10, 0.5, "x")], (100, 100))
+        self.overlay.clear()
+        assert self.overlay._detections == []
+
+    def test_visible_by_default(self) -> None:
+        assert self.overlay.visible is True
+
+    def test_multiple_detections_stored(self) -> None:
+        dets = [
+            Detection(0, 0, 50, 50, 0.9, "label"),
+            Detection(100, 100, 200, 200, 0.75, "label"),
+        ]
+        self.overlay.on_detections(dets, (640, 480))
+        assert len(self.overlay._detections) == 2
+
+    def test_replace_detections_on_new_call(self) -> None:
+        self.overlay.on_detections([Detection(0, 0, 10, 10, 0.5, "x")], (100, 100))
+        self.overlay.on_detections([], (100, 100))
+        assert self.overlay._detections == []
+
+
+class TestBboxOverlayCoordinateMapping:
+    """
+    Verify that BboxOverlay correctly maps source-frame pixel coordinates
+    onto the letterboxed video_rect when painting.
+
+    We don't test actual QPainter output — instead we verify that the
+    QRect values passed to painter.drawRect() correspond to the expected
+    scaled coordinates.
+    """
+
+    def setup_method(self) -> None:
+        self.overlay = BboxOverlay()
+
+    def _make_painter_mock(self):
+        painter = MagicMock()
+        fm = MagicMock()
+        fm.height.return_value = 14
+        fm.ascent.return_value = 11
+        fm.horizontalAdvance.return_value = 60
+        painter.fontMetrics.return_value = fm
+        return painter
+
+    def test_paint_skips_when_no_detections(self) -> None:
+        painter = self._make_painter_mock()
+        self.overlay.paint(painter, QRect(0, 0, 640, 480))
+        painter.drawRect.assert_not_called()
+
+    def test_paint_skips_when_source_size_empty(self) -> None:
+        # detections present but source_size not set
+        self.overlay._detections = [Detection(0, 0, 100, 100, 0.9, "label")]
+        painter = self._make_painter_mock()
+        self.overlay.paint(painter, QRect(0, 0, 640, 480))
+        painter.drawRect.assert_not_called()
+
+    def test_bbox_scaled_to_full_video_rect(self) -> None:
+        """
+        Source: 640×480, covers full frame.
+        video_rect: 640×480 at origin.
+        Detection: full-frame box → should map 1:1.
+        """
+        self.overlay.on_detections(
+            [Detection(0.0, 0.0, 640.0, 480.0, 0.99, "label")],
+            (640, 480),
+        )
+        painter = self._make_painter_mock()
+        video_rect = QRect(0, 0, 640, 480)
+        self.overlay.paint(painter, video_rect)
+
+        # First drawRect call = the bounding box
+        first_call_rect: QRect = painter.drawRect.call_args_list[0][0][0]
+        assert first_call_rect.x() == 0
+        assert first_call_rect.y() == 0
+        assert first_call_rect.width() == 640
+        assert first_call_rect.height() == 480
+
+    def test_bbox_scaled_with_half_size_video_rect(self) -> None:
+        """
+        Source: 640×480, video_rect: 320×240 at origin (0.5× scale).
+        Detection at (64, 48)→(128, 96) should map to (32, 24)→(64, 48).
+        """
+        self.overlay.on_detections(
+            [Detection(64.0, 48.0, 128.0, 96.0, 0.8, "label")],
+            (640, 480),
+        )
+        painter = self._make_painter_mock()
+        video_rect = QRect(0, 0, 320, 240)
+        self.overlay.paint(painter, video_rect)
+
+        first_call_rect: QRect = painter.drawRect.call_args_list[0][0][0]
+        assert first_call_rect.x() == 32
+        assert first_call_rect.y() == 24
+        assert first_call_rect.width() == 32   # (128-64) * 0.5
+        assert first_call_rect.height() == 24  # (96-48) * 0.5
+
+    def test_bbox_offset_by_video_rect_origin(self) -> None:
+        """
+        video_rect at (100, 50) — letterboxed with margins.
+        Detection at origin of source should map to (100, 50).
+        """
+        self.overlay.on_detections(
+            [Detection(0.0, 0.0, 100.0, 100.0, 0.9, "label")],
+            (640, 480),
+        )
+        painter = self._make_painter_mock()
+        # video_rect 320×240 starting at (100, 50)
+        video_rect = QRect(100, 50, 320, 240)
+        self.overlay.paint(painter, video_rect)
+
+        first_call_rect: QRect = painter.drawRect.call_args_list[0][0][0]
+        # x: 100 + int(0 * 320/640) = 100
+        # y:  50 + int(0 * 240/480) =  50
+        assert first_call_rect.x() == 100
+        assert first_call_rect.y() == 50
+
+
+class TestBboxOverlayWorkerPacket:
+    """Test FramePacket and ResultPacket data structures."""
+
+    def test_frame_packet_fields(self) -> None:
+        from app.inference.worker import FramePacket
+        pkt = FramePacket(
+            frame_id=1,
+            raw_bytes=b"\x00" * 12,
+            width=2,
+            height=2,
+            channels=3,
+        )
+        assert pkt.frame_id == 1
+        assert pkt.width == 2
+        assert pkt.channels == 3
+
+    def test_result_packet_fields(self) -> None:
+        from app.inference.worker import ResultPacket
+        pkt = ResultPacket(frame_id=5, detections=[], width=640, height=480)
+        assert pkt.frame_id == 5
+        assert pkt.detections == []
+        assert pkt.width == 640