I probably figured it out. I read the main directories folders with "read file info" then pick random element from that, then use that as a variable for open file result, with the name of the image or video of the file you want to post directly after the variable in the text box for "open file result". You have to prename your files to have this run and choose random folders within a folder.
If anyone has a better way, please let me know! Thanks!