Audio and gameplay stutters with Lightning and USB-C accessories

[hstr33t]

Problem Description

iOS game exhibits stutters in background audio approximately every 15 seconds when Lightning headphones are plugged in to iPhone 11 Pro. In addition, stutters are exhibited when Lightning-to-USB 2.0 cable is plugged in (even with nothing attached to the USB end).

The issue appears to affect iPhone 11 Pro (iOS 13.3) but not most other devices (e.g., iPhone X, iPhone 7, iPhone 6s Plus, iPhone 6, iPhone 5s, iPad mini 2, iPad Air 2, iPad Pro 10.5-inch are all okay — have not tested iPhone 8, iPhone XR, iPhone 11). Restarting iPhone 11 Pro does not resolve the issue. Re-installing the app does not resolve the issue.

Plugging in with Lightning results in stutters about every 15 seconds (although it is somewhat irregular). Unplugging results in no stutters. This test was repeated numerous times with different sets of Lightning headphones and USB cables. This issue is not exhibited in other apps/games run on the iPhone 11 Pro. And the issue is not exhibited when bluethooth headphones are used.

Has anyone else observed this behaviour?

We're using:
AIR SDK 33.0.2.338
Starling

Steps to Reproduce

• Launch iOS app on iPhone 11 Pro (iOS 13.3) — a AIR game running background music will make it obvious if a stutter occurs
• Plug in Apple Lightning headphones (or Lightning-to-USB 2.0 cable)
• Wait and listen for stutters for at least 60 seconds

[hstr33t]

Confirmed that this is still happening under iOS 13.4.1 and AIR 33.1.1.98.

[hstr33t]

Confirmed that this is still happening under iOS 13.6 and AIR 33.1.1.190.

Would love to know if anyone else is (or isn't) experiencing this issue. To test, all you need is an iPhone 11 Pro (or possibly another recent device) and an iOS AIR game that has sounds and/or music.

It doesn't need to be Lightning headphones (although that's easy to test). The stuttering will occur if you simply plug in a Lightning-to-USB cable (with nothing attached to the other end). When the cable is unplugged, the stuttering stops.

[hstr33t]

Confirmed that this issue is happening with an iPhone 11 (in addition to iPhone 11 Pro), so this makes two separate, recent devices that are exhibiting this issue. The hiccup/stutter affects animation and gameplay, not just audio.

[hstr33t]

Confirmed that this audio stutter is still happening with iOS 15.1 + AIR 33.1.1.633.

Facts remain the same:

• Anything plugged into the Lightning port (Apple headphones, or even just a Lightning cable with nothing plugged into the other end!) causes the stutter to happen about once every 30 seconds or so.
• Applies to more recent devices (e.g., iPhone 11, 11 Pro, XR and later), not not to earlier devices.
• Unplug from the Lighting port and the stuttering stops (in real time).

[hstr33t]

Confirmed that this issue happens with iPad mini 6 running iOS 15.2 with USB-C-to-headphone dongle...

[ajwfrost]

@hstr33t are you able to check with AIR SDK 50.2.4.3 (or later) please? I am wondering if this is also fixed by the change we put in for #2642...

thanks

[hstr33t]

@ajwfrost, it could be a few weeks until I'm able to do this but I will post here as soon as I do. Thanks very much for following up on this.