Yes you’re right. You do not need those plugins.
Instead you have have something like:
appsrc -> nvvideoconvert -> nvstreammux -> nvinfer -> nvstreamdemux -> nvvideoconvert -> nvdsosd -> ..
You can use appsrc’s signals to send in buffers whenever you want. You can check the signal 'push-buffer. This takes in a GstBuffer.
This example here shows how to push a numpy array in the pipeline Appsrc with numpy input in Python - #8 by gautampt6ul.