PS4 HDMI out
PC HDMI out

2D/3D content, FullHD

connect to a MagicBox
that acts like TrinusVR ( http://trinusvr.com/ )..
you can adjust everything to use any headmount display.
The MagicBox captures the input stream and makes halfSBS (or others)
To make all adjustment and settings, you can plugin USB mouse/keyboard and an monitor via HDMI to have screen where you control the settings for output.

The output goes over
– Wifi 2,4/5/60GHz,
– USB using smartphones tethering capabilities
– HDMI

if someone would need to add two displays, to use one for left eye and one for right eye.. then we would need usb and hdmi outputs twice, and some settings more
( 2x samsung S6 with stunning resolution ppi ;o) )

So we could use any smarthphone as head mounted display, with 2D or 3D content.
So far without headtracking.
You need headtracking?  Playing Car or Flight simulators?
No problem, you could use external sensors like ZEISS Cinemizer USB headtracker or even sensors from smartphone itself, if industrie/programmer would support.
Imagine your smartphone send sensor data via wifi to and USB stick which emulates Mouse input… but maybe your smartphone sensors are ugly.. drifting.. so you would need a sensor like ZEISS Cinemizer USB headtracker, maybe even smaller and without cable.

Back to the box.. who could build such a box ?
Maybe proffessionals like team from
https://www.blackmagicdesign.com/de
https://www.blackmagicdesign.com/de/products
https://www.blackmagicdesign.com/de/products/intensity
they have the technology of streaming and capturing, but they would have to add new VR virtual technology like TrinusVR already represents.

in case of cabled output using HDMI…
there is a problem today,
were are 5″-7″ fullHD displays with HDMI input?
i have not found them yet..