There are several ways to design and integrate video and telemetry together with RPI, i will try to describe my findings and hopefully save many for time and money. First of all i will give a huge thanks to my friend @Tommy_Larsen for all the effort he has put into this system. He stands for most of the testing and RPI solution in this site.
In my first cellular UAV setup i was using RPI with LOGITECH HD PRO WEBCAM C920 connected to RPI via usb interface. I was surprised by how good the picture quality was and i definitely would recommend this camera.
I was using gStreamer to grab my USB video and generated a pipeline-stream to my Ground control station.
I connected telemetry TX/RX wires from APM 2,6 board directly to my RPI TX/RX pins and used ser2net software which converts the serial data to net using TCP protocol. Unfortunately i was not able to get ser2net working with UDP protocol and since my cell vendor is not giving me static IP address, i was forced to use DynDns for connecting Mission Planner to APM.
For cellular network i was using ZTE MF821D 4G usb adapter and sakis3g software . Sakis3g has nice user interface which make it easy for everyone to configure correctly.
Keep in mind that Raspberry PI needs external power supply feeding USB adapters and the chipset. Im using 5v 5Amp bec.In my ongoing and present project im using GoPro and Easycap video grabber connected to my RPI. This will give me the opportunity to record HD during flight and hopefully stream even better pictures than Logitech Web cam. Im also using TTL to Ethernet adapter for my telemetry data instead of ser2net in my last project. TTL to ethernet adapter supports UDP protocol which is in my opinion the best for this project.
Latency test using gamepad & cellular network.
This test is showing the latency using cellular network and gamepad controller.