Evaluate how/if WebXR should interact with audio-only devices.

[toji]

At some point we should do an evaluation of whether or not the WebXR API is appropriate for use with audio-only "AR" devices. (Like these Bose glasses)

This issue is effectively splitting a portion of the conversation out of #815, where the conversation has been mostly focused on using the existing API on existing hardware without a dependency on rendering. I'm going to set this to the "future" milestone immediately because the hardware that operates in this modality is rare and none of it is consumer-facing that I'm aware of, but I think it's reasonable to expect that to change over the next few years.

Copying some additional comments of mine over from that thread:

Based on the information that I've been able to find about audio-only AR (like the Bose glasses) I'm not entirely sure how they perform their location-based functions. I would actually be surprised if it was built around any form of real positional tracking, and am guessing it's more along the lines of Google Lens which surfaces information based on a captured image with little understanding of the device's precise location. In any case, I'd love to know more about how existing or upcoming non-visual AR devices work so we can better evaluate what the appropriate interactions are with WebXR.

Now, ignoring the above questions about how current hardware works, if we assume that we discover a device that provides precise positional tracking capabilities but has no visual output component we can brainstorm how that would theoretically work out. While it's not clear how web content would surface itself on such a device, it seems safe to say that traditional immersive-vr style content wouldn't be of much interest, and so we'd likely want to advertise a new session mode explicitly for audio-only sessions. Let's call it immersive-audio. Once that's established the various text tweaks David mentions would be appropriate, but from a technical point of view the biggest change would be that an immersive-audio session wouldn't require a baseLayer in order to process XRFrames. Instead we would probably just surface poses via requestAnimationFrame() as usual and allow Javascript to feed those poses into both the WebAudio API for spatial sound and to whatever services are needed to surface the relevant audio data. There's also some interesting possibilities that could come from deeper integration with the audio context, like providing poses directly to an audio worklet.

Regardless, given the relative scarcity of this style of hardware today and the large number of unknowns around it I don't see any pressing need to move to support this style of content just yet. It's absolutely a topic that the Working Group should follow with great interest, though!

[frastlin]

Here are some devices I have found that use audio only with head-tracking:

• See Munkey headset
• Audeze Mobius headphones
• Nx Head Tracker
• EDTracker
• Mimi Hearing Technologies (They purchased 3D Sound Labs, so they have the ability somewhere)
• Redscape

And here is an article talking about other headphone projects that failed.

I am personally using my phone as a head tracker and placing it somewhere on the head.

But head-tracking technology is not expensive and headphones are decades ahead of visual displays when it comes to quality and acceptance, so I would not be surprised if head-tracking just becomes something all headphones have in the near future, similar to smartphones.

[frastlin]

I think a mode, that is different from the existing two modes, that only exposes sensor and positional data, would work for handling devices that do not have a visual component:
#926
It would also handle applications that would like to run the graphics through the GPU once that is created.

[frastlin]

Hello,
An update on audio only devices:
"AirPods (3rd generation), AirPods Pro (all generations), and AirPods Max use Spatial Audio and head tracking to create an immersive theater-like environment with sound that surrounds you."
It is estimated over 150 million AirPods have been sold (although not all of them include head-tracking).
Regardless, I think this by far makes AirPods the most ubiquitous VR headset in existence, as multisensory VR headsets only sell around 8 million units a year in aggregate.
Now that so many people have fully functional audio only VR headsets, it would be prudent to cater to this significantly larger market for WebXR experiences.

[AdaRoseCannon]

/facetoface sounds like a could be a good discussion

[JaredMonkey]

Adding an example of folks on the native side hooking into Airpods:
https://github.com/anastasiadevana/HeadphoneMotion