Correct.
Some phones can output HDMI through their USB port but then you would not have any way to connect to the DJI controller. Not sure a hub would pass all the data and HDMI but may be possible. I have an old Motorola phone that has a separate HDMI port but it is too slow for use with any drone.
Some tablets have both a USB and a HDMI port. I have a Nvidia Shield K1 that has both and would solve your current problem. But personally I prefer a smaller monitor (phone size) for my Mavic and Spark. I also use my
BT-300's with all my drones but I am hoping Epson will release and sell an adapter that will allow me to use the
BT-300 glasses with HDMI.
I know that the
DJI goggles can connect to the Mavic but there must be some magic going on in the
goggles to make this happen. I wish DJI would release an HDMI adapter for the Mavic.
~Bill