How do i build an action for subject extraction and saving to a png with a transparent background?

Hi - I need some help!  I have an action of automated subject extraction and then putting them on a transparent background.  However, I would like to automate this (batch) and save it to a png.  I would like to batch-process 100's of files to extract and save the subject into a transparent png - that's the end goal.  Automating the saving of a png with the transparent background has me stumped.  Can someone share how this is done?  Thanks!