I think the only HDMI available to your remote is the DJI one for about $100. Need a very small metric hex wrench to get the four screws out of the bottom of the white cover and a small crosspoint screwdriver for the board screws. The HDMI has two circuit boards and you nee d to pry them apart to install one, and then snap the outer one on top and reinstall the new cover. There are also three ribbon cables that need the little latches flipped up to remove/install those cables.
Only other thing I've heard of is the nVidia Shield K1 tablet that has a mini-HDMI output jack for the feed and it might be higher rez (1080) than the 720 out of the DJI one for the older P3/P4. If you have fancy goggles that upscale and larger screen (Royole Moons ~$800) you probably will not notice it.
I did try the Apple A/V converter too that is about $49 but it is only a HDMI output of the iPad. There is a Lightning input jack on it where I thought I could run the remote controller's USB to Lightning cable into the A/V converter, and then from that onto the iPad. That way I thought I would be able to use the HDMI jack to get the HDMI feed to the goggles from the remote and on the iPad both. Doesn't work. The Lightning input on the A/V converter is only for charging and not data transmission from the remote via USB as normally used.
When I installed the DJI HDMI, for whatever reason, the remote went back to I guess it's factory firmware which showed up as 1.60+ and not 1.80. I should have not upgraded to 1.80 as it asked later to upgrade, and I did, and now the video breaks up with 1.80. From what I've gleaned 1.60 seems less buggy than 1.80 with regards to video lag. I've seen reports of other versions like 165 but seems the jump was back to stock (1.60+ mine) and only to 1.80 and nothing in between.
Live and learn with the buggy DJI software updates.
