For voice I can highly recommend Mumble, it's trivially self-hosted too and feels well integrated on all platforms.

For video though your options are definitely more limited, keep an eye on Riot, I'm not sure that it's ready yet, but when it is it will present an extremely good option. If you only need mobile, Signal does it today and is probably one of the most stable and secure products around, can't vouch for the video quality though personally.