For preprocessing, it will keep aspect ratio and then resize and pad. Reference:Inferring Yolo_v3.trt model in python - #26 by Morganh
For how to process the trt engine, when you read GitHub - NVIDIA-AI-IOT/deepstream_tao_apps: Sample apps to demonstrate how to deploy models trained with TAO on DeepStream, you can also refer to other user’s experience in Inferring Yolo_v3.trt model in python (for yolo) and Inferring detectnet_v2 .trt model in python - #46 by Morganh (for yolo and detectnet_v2) and Run PeopleNet with tensorrt - #21 by carlos.alvarez (for detectnet_v2)