It appears that Safari 11 on iOS will pause the video capturing during a WebRTC session when the browser/tab is moved into the background; meaning the remote client will just see a black image unless the video capturing browser tab is currently in focus. I can understand why it would do that*, but I could not find any official statement or documentation about this behaviour.
* (Both for privacy and resource conservation reasons.)
Is this the expected behaviour or is there anything that can be done about this?
It looks like expected behavior in our experience. Similarly, a native iOS app cannot capture video while in background.
The behavior is the same on other platforms, e.g. Chrome on Android - both when backgrounding the browser or the WebRTC tab.