One thing that you guys may have missed is that there is a file naming standard defined by Plex Inc for having the PMS server recognize media as being in 3D format and allowing Plex clients which support this usage to send the appropriate HDMI commands that can switch a TV set or projector/receiver into the correct rendering mode.
Typical usage examples that work with OpenPHT/RasPlex: (used in my own Plex library)
Dragon Blade (2015).1080p.3D.htab.mkv
Here the 'H' in "hsbs" or "htab" stands for "Half", as these formats use normal sized frames to hold both the left and right eye pictures combined but compressed horizontally or vertically (respectively) to half the original size.
The "tab" and "sbs" formats instead use double-height or double-width sized frames so as to hold both the left and right eye pictures combined without any loss of picture quality.
There is also a format using sequential frames that alternate between left and right eye pictures, but I am not certain if this mode is supported by OpenPHT.
Best regards: dlanor