retained threadedvideowriter

backend/engine.py

@@ -1,6 +1,8 @@
 import os
 import time
 import tempfile
+import threading
+import queue
 import numpy as np
 import cv2
 from collections import defaultdict
@@ -20,9 +22,6 @@ def _point_to_segment_dist(px, py, ax, ay, bx, by):
     return np.linalg.norm(P - (A + t * AB))
 
 
-import threading
-import queue
-
 # Lightweight drawing colors (BGR for OpenCV)
 _CLR_BOX = (230, 180, 50)     # teal-ish
 _CLR_LINE = (80, 220, 100)    # green
@@ -150,7 +149,7 @@ def run(model, video_path, line, config, on_frame, save_annotated=False, annotat
     results = model.track(
         source=video_path,
         tracker="bytetrack.yaml",
-        imgsz=640,    # Optimized from 736 for real-time performance on CPU
+        imgsz=736,    # MUST match OpenVINO export imgsz — compiled graph is fixed shape
         conf=config.get("conf", 0.12),
         iou=config.get("iou", 0.6),
         vid_stride=stride,