[Bug] Background tabs stop playing media after some time

[kawaiiDango]

Steps to reproduce

1. Open a page playing media. I tried https://www.seraph.jp.net/blinddark
2. Open some sites (I tried Google searches) in 2-3 more tabs.

3a. The background tab playing media gets unloaded and the audio stops after about 40 secs. (When you select the tab with the media, the page reloads from scratch)
or
3b. Make sure that the tab playing media isn't the currently selected tab. Press back so that the app goes into the background. (3a) happens.

Expected behavior

Background tabs playing audio/video should not unload, until the playback is complete, just like Firefox desktop.

Actual behavior

Device information

• Android device: OnePlus 6, Android 10
• Fenix version: Nightly 200402 18:00 (Build #20931806)
  38.0.20200402130113, ea47f9c33

┆Issue is synchronized with this Jira Task

[Mentis]

Might be related to #9039

[buttercookie42]

just like Firefox desktop.

... or Fennec (tabs playing audio were specifically protected from being unloaded).

[miketaylr]

As reported in webcompat/web-bugs#48003, I can reproduce this same issue when switching tabs, or backgrounding the app. Audio stops around 20 or 30 seconds later.

[kawaiiDango]

I also noticed that background tabs get unloaded even when there's unsaved form data. I was writing an email, searched and copied stuff from another site and when I returned, everything was gone.

This is actual data loss and should be fixed.

[lobontiumira]

I reproduced this again today, on the latest Nightly build from 7/9 with Google Pixel (Android 10).
I had rockfm.ro opened in a tab, left Fenix in the background. After a while, 10-15 minutes, the media stopped. I had to refresh the tab and press play again.

[aroskuski]

I can reproduce this behavior with YouTube if I load the Video Background Play Fix extension via web-ext. The tab doesn't necessarily unload, but it does appear to stop whenever the video needs to buffer until I switch the tab to the foreground again.

[buttercookie42]

I wonder whether background tabs are marked as inactive (i.e. JS timeouts suspended amongst other things) even when they're playing back media? That would seem a conceivable explanation for pages loading the media using their own custom logic, like e.g. Youtube.

[aroskuski]

@buttercookie42 That definitely seems plausible. I just tried the player at http://audiocogs.org/codecs/flac/ (I think the other codecs on that site behave the same way if you don't have any FLAC files), which implements the audio playback entirely in JavaScript, and that stops immediately upon the tab losing focus, instead of continuing for a bit and then stopping. I'm not sure if there are any relevant technical differences between what that site is doing and normal video/audio tags, but it definitely seems to point to JavaScript not being run for background tabs playing media being at least part of the problem.

For comparison, the audiocogs players do keep playing in background tabs in Fennec.

[robsmith11]

I experienced this as well when using YouTube in desktop mode.