Microsoft just announced an update around the HoloLens that allows you to share on what you are seeing (from a first-person perspective) with others to make to more interactive. This is a combination of MRC (Mixed Reality Capture) which already exists and some new updates that address some of the short coming of the MRC - especially when working with a audience.
The main use case on the spectator view - as the name suggests is to allow those in the room not wearing a device to see the holograms but also the interactions that the folks wearing HoloLens with their mixed reality experience.
You can use this to capture a mixed-reality scene, live stream the content (say in a meeting / conference), and, shoot/record the video. This essentially is the ‘cheap’ version of the special camera rig that Microsoft uses for keynote presentations.
It is not as straight forward as you might imagine; but at the same time if you are doing this ‘properly’ it isn’t as complex as well. You need some special equipment, and need to change some configuration, and add details to your apps to account for this.
You do need some special DSLR cameras (with HDMI output), and some other hardware - details can be found here. You can also 3D print the mount (STP can be found here ).
And in addition there are a bunch of other steps that you need to do - from calibrating (to get the offset from the camera), to the Compositor (which is a unity extension) and allows you to record the video and change the hologram opacity, spatial mapping data details, etc.