Hardcode subs into mutiple mp4 file at once?!

I have search for a while now and didn't find anything similar or maybe I didn't searched enough but I want to hardcode over 12k of mp4 files , so I wonder what is the most easy way to do it ? Is there a program or a script that can detect the mp4 file and subtitle file and hardcode multiple video files ? Like a batch script or something. But also with the possibility to set the font size and style. Even if it's a software that you now , I will buy it if it's doing the job.

Thanks,