Take a look at the EZ Wifibroadcast project, a DIY hd transmission made from RaspberryPi, cheap wifi dongles.
It works on 2.3/2.4/5.8 Ghz Bands.
Video transmission latency is about 130ms.
Diversity video reception
OSD with support for Mavlink protocole, etc........
been looking at a Joule for video processing, its the transmission part I am hung up on. I read that documentation but it is not very easy to follow, plus I have 0 Pi experience.
I am not worried about osd, I usually fly with tower and a tranis, so get plenty of telemetry. I just need video feed for framing