What's the best way to get preview to RJ45?

I'm working on a project rather than a repair- but ultimately I need to find a slick way to get the preview video stream to a wired ethernet (RJ45) port. Ultimately I want to continue saving HD video to memory but send out the low res preview over the ethernet instead of via wifi. Any suggestions for that? Worst case scenario I could use a Raspberry pi, but I was hoping for something more compact and module-like.