Which platfrom and deepstream version are you using? Seems you are using DS6.1 or later.
Please be noted that by default PERF is set to FALSE, meaning nvurisrcbin will not be used, the decodebin will still be “uridecodebin”.
Documentation for nvurisrcbin: NvDsSourceExt — DeepStream 6.1.1 Release documentation (nvidia.com), and
please refer to DeepStream 5: deepstream-app yoloV3 with video stream from camera - #6 by mchi for setting usb camera.