Pure sharpness ranking fails when a moving car causes motion blur — blurry car frames score lower than the sharp static background, so YOLO never sees the vehicle. Now compute inter-frame motion diff (downscaled to 320px, fast) alongside sharpness, then combine (65% motion + 35% sharpness) to select the top 15 frames for YOLO. This ensures the vehicle-present frames reach YOLO and PlateRecognizer even when they are slightly blurred. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>