Clarify when to fire devicechange event for changes of device capabilities

[youennf]

Devices may not be added or removed but their capabilities or labels may changed.
In that case, it might be good to fire a devicechange event provided labels are exposed.

[guest271314]

Devices can be added and removed. Plug and play USB devices, Bluetooth devices, virtual devices. Firing devicechange has nothing to do with listing the incorrect device if incorrect device is still listed.

[guest271314]

The issue is Chromium refuses to list or capture audio devices that include monitor text in device description at Linux. To workaround that arbitrary restriction it is possible to dynamically change and set the devices being captured to a monitor device https://bugs.chromium.org/p/chromium/issues/detail?id=931749, thus, when the device changes not only must a devicechange event be fired but also the correct device being captured needs to be listed at enumerateDevices(), in spite of Chromium in-house decisions imposing restrictions of device capture. Firing devicechange alone in this case will not solve the bug that #693 was filed for if the exact same devices are listed.

[jan-ivar]

I think we have to be careful not to disturb what I think is the primary use case of devicechange:

• Detecting user insertion (or bluetooth activation) of a new device (meaning: user intends to use this device)

Recall: the event is insufficient, apps must diff enumerateDevices results (after gUM grant!) before and after the event.

Hopefully apps are diffing only on deviceIds. But if they're not (diffing on the entire entry or label), then changing a label may trigger a false positive insertion (apps thinking the user wants to use new device when they don't).

[alvestrand]

Not clear how properties such as label would change, or whether browsers would be able to detect it (apart from polling).

[jan-ivar]

This seems like a user agent configuration issue, and it's not clear there's value in standardizing what they should do here. Closing as no action needed.