When making calls on iOS Web and switch Safari to background, audio cannot work properly.

[Eddy0644]

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Steps to reproduce

1. Set up a NC server, use a Windows Chrome as user1, iOS Safari app as user2 (guest)
2. Make a call, verify that all video and audio functions are operational.
3. Switch Safari app to backend / lock the device's screen.

Expected behaviour

Even the browser is in backend, the audio functions should work correctly.
( I believe this is not a browser issue, because another web calling repository, VoceChat, can still send and receive audio correctly while in background, so I think there is a way to solve it.)

Actual behaviour

While in background, the iOS device cannot hear from others (maybe eternal loop of the last 1-second sound) but others can hear from iOS.

Browser

Microphone available: yes

Camera available: yes

Operating system: iOS

Browser name: Safari (along with iOS 15.6.1)

Server configuration

Nextcloud AIO v10.4.0 on Ubuntu 20.04, all containers up-to-date
All settings about Talk are kept default, and STUN, TURN, High-performance backend have been setup on the same server.

For the server log, I think it isn't relevant for this case, because this seems to be a client-side issue.

[nickvergessen]

For the server log, I think it isn't relevant for this case, because this seems to be a client-side issue.

Most likely true. Is there anything in the browser log?

Also can you add which version of Nextcloud and Talk you are running?

[Eddy0644]

Thanks for attention.
I have no idea how to check for browser logs on mobile Safari. Maybe there is a way to retrieve on PC but it must be sophisticated.
And on Android devices this issue disappears, at least the browser is running without limitations in background.
Nextcloud version: 30.0.5
Talk version: via docker image 'nextcloud/aio-talk:latest' 2 days ago, I don't know how to check for its version.
"nextcloud/aio-talk@sha256:3ef3fb880bc61e35b18aeda360c338c158487a1524018f9307aa58566e4da8e0"

[SystemKeeper]

Mobile Safari logs can be accessed from a Mac with Safari (if enabled in the iOS settings).
Any reason you're not using the Talk iOS App?

[SystemKeeper]

I just tried it (although with an iOS 18.2.1 device) and couldn't reproduce the behavior. The camera turns black, but audio worked in both direction. Would you be able to test with a different iOS device that has a newer iOS version installed?

[Eddy0644]

I recently used an iOS 16.x device and could not reproduce the issue, too. So this turns out to be an issue only on an outdated WebKit?
Also I found this: https://doc.shengwang.cn/doc/rtc/javascript/overview/browser-compatibility (Chinese Webpage)
I don't know if this information can help you. Thanks.

When the browser or app switches to the background, the audio stream is interrupted
Affected by: Safari on iOS 15.x; Apps with WKWebView embedded on iOS 14.4 through 15.x (e.g., WeChat browser and Chrome browser).

Causes:
Safari: Due to a bug in WebKit, WebAudio's AudioContext stops audio processing when the browser switches to the background.
Apps with embedded WKWebView: iOS WKWebView does not allow the microphone to be used in the background, see Apple's forum description Microphone gets muted in background.
Workaround: Apps embedded with WKWebView can't circumvent this issue at this time. Safari on iOS 15.x can circumvent this issue by following these steps:
Upgrade to Web SDK 4.7.3 or later.
When you call createMicrophoneAudioTrack to create an audio track, set the bypassWebAudio parameter to true, and the local audio stream will be published without being processed by WebAudio. Note that this scheme will cause the mixing function (MixingAudioTrack) to fail.

[Antreesy]

Thanks for the research, I was also checking in parallel, and bump into follow-up to the bug mention by you, and seems to be fixed for iOS 16.1+: https://bugs.webkit.org/show_bug.cgi?id=237878

AudioContext was introduced in Talk recently, to fix problem for Safari users not hearing another participants, if it's in background: https://github.com/nextcloud/spreed/pull/12497/files . So far there were no complains regarding this on up to date devices.

Note that this scheme will cause the mixing function (MixingAudioTrack) to fail.

This might revert all efforts made by recent PR. So I'm afraid, this will not be a priority to implement by us. Since iOS 16 is supported by devices down to 2016 y.o., the best would be to update to a more recent iOS version.