How to add custom compression / decompression?

Hi all! I have all my data stored in an S3 bucket and I would like to use Hub to load my data from S3, yet my data on the cloud is compressed using [Jetraw by Dotphoton](https://www.jetraw.com/) and I would like it to decompress the images as I am pulling them from the cloud. I would be ready to write code to make this happen, but as I am new to the code base I would like to know where this would fit in the most and where I should start. Thank you all in advance!