Offline Program to convert Images from PNG to WEBP for MacOS

Is there an offline program that let's me convert my png files to webp? I'm ruing MacOS X 10.11 El Capitan.

Searching on google I was only able to find online converters that shrink the size of the Image and do not let me upload more than one file at once. This is a problem since I have around 800 pngs to convert.