This is iOS10 only, but playing audio in background tabs is something that we've cared a lot about in the past.

I'd like to investigate for M69 if we can.  Assigning to someone who has access to the MTV device cabinet to start.

The bug says: "reproducible on the current stable build", "Working fine in Chrome Old UI", and "not a regression". These 3 seem like contradict each other.

Is this bug reproducible with M68 stable and default flags?
Is this bug reproducible with M68 stable and ui-refresh-phase1 enabled?

Bug reproducible on the current stable build :M68, No (with or without UI-Refresh flag)
Bug reproducible on the current beta channel build :M69, Yes (with UI-Refresh flag enabled)

Thanks for checking. Could you please bisect good and bad git version.

Revision Number for 69.0.3493.0 (Good Version) - 7066e7628789
Revision Number for 69.0.3494.0 (Bad Version) - 27a4cd8f3d84

Thanks for bisecting. The only suspicious ios change I see is this one:
https://chromium-review.googlesource.com/1135135

That CL is even more suspicious given that playback stops after interacting with tab switcher. Ed, or Mark can you investigate further?

Mark, do you think that tab grid transition API change could have affected this?

This repros for me with UIRefresh *off* (on trunk). That is, either with or without the UIRefresh flag, YouTube videos pause when entering the tab switcher on iOS 10.3. (I tested in the simulator).

Removing the UIRefresh label, still RBS.

(I also verfied that this bug happens with slim navigation enabled or disabled, so that's not the culprit).

Stable cut is in 1 week. Is there an update here?

Punting to M70.

Problem seems to be associated with the tab grid animations, so remarking as UI Refresh-related.

I have tested for YouTube:
m68 on iPhone8/iOS11.4: not working on old/new UI;
m69 on iPhone6sp/iOS11.4: not working on old/new UI;
m70 on iPhone7simulator/iOS10.3: not working on old/new UI;

I think this depends on the behavior of the site, while some sites work well and YouTube does not. You can create a local webpage with <video> refers to a local mp4 file and it won't pause when switching tabs. YouTube maybe just pause the video in "window.onblur" event, which will be emitted when current WKWebView loses focus.

Youtube is a bad test case for this bug.  Youtube intentionally pauses playback when the tab loses focus, unless you pay for Youtube Premium.

Perhaps try testing with vimeo or some other video provider?

I've tried some video sites I often visits and my test website with a mp4 <video> , they works fine. I tried vimeo just now and it works fine.

Can I mark this as WontFix now?

Can we test if this bug is reproducible with YouTube Premium?

Checked. YouTube Premium works fine. Glad that YouTube has a free trial, otherwise we have to pay €11.99 for this bug :D