nvinfer plugin and low-level lib are opensource. the default postprocessing function is ClassifyPostprocessor::parseAttributesFromSoftmaxLayers. which can procss this kind of output
/* outputCoverageBuffer for classifiers is usually a softmax layer.
* The layer is an array of probabilities of the object belonging
* to each class with each probability being in the range [0,1] and
* sum all probabilities will be 1.
you also can add custom postprocessing function. please refer to this topic.