I am trying to flash openhd on tv box,
Do I need to flash armbian on the mmc of board or does openhd has a similar operating system that will boot ?
OpenHD is more like an operating system, that can be flashed to supported devices. SBC's - OpenHD
It is also possible to port OpenHD to new hardware, but this is much more work than you think.
We have a little guide how to port openhd, keep in mind, it is made for experts and is no step by step guide. More a list of thigs that are minimaly required to run openhd at all.