If you don't have a headset, Mixed Reality isn't quite the spectator sport that Virtual Reality is. VR lets users easily output their entirely digital world to another display from their PC for others to look at. In MR, the headset is often self-contained and utilizes real world imagery.
As a result, showing a non-user what's happening can be difficult. In its demos, Microsoft usually mounts a HoloLens to a DSLR with a special lens setup. For the general user, that isn't at all practical.
As a result, Microsoft is letting devs create a bespoke Spectator View app on iOS. Rather than a complex rig, users can simply point their phone and see the same elements like everyone else.
Recording and Live Stream Features
Importantly, you'll also be able to record. In enterprise scenarios, this could be invaluable, with full-HD capture and even an option of shadows and anti-aliasing to increase the fidelity.
Spectator View uses WiFi to do so and is also able to stream directly to Apple TV. Guests can finally see the fun users are having, and businesses could even be given a semi-virtual tour of proposed changes to a space.
The main restriction is that you must have an ARKit-enabled iPhone or iPad, which means you need an iPhone 6s or above. The application will automatically handle sessions, ensuring users are added to the correct one and everything is synchronized.
You can find more information about creating an app on the Microsoft blog.