iOS Unity 6 crash in ec_tell_frac: IosLinkOrderDiagnostics does not handle libGameAssembly.a

[DongYeongJeong]

Summary

Our Unity iOS application crashes only on iOS when LiveKit audio is initialized or when a remote audio track is subscribed.

Android builds using the same LiveKit integration work normally.

The crash consistently stops in UnityFramework at the Opus/CELT symbol ec_tell_frac, suggesting a native codec object/symbol conflict.

Environment

• LiveKit Unity SDK: 2.0.0
• Unity: 6000.5.5f1
• Scripting backend: IL2CPP
• Architecture: arm64
• Target: physical iOS device
• iOS deployment target: 15.0
• Installation: UPM Git URL (https://github.com/livekit/client-sdk-unity.git)

Symptoms

We observed crashes at multiple audio lifecycle points:

1. Immediately after local microphone initialization:

LiveKit: Configured native audio source with sampleRate 48000 and channels 2
LiveKit.RtcAudioSource:ResolveDeviceFormat()
LiveKit.RtcAudioSource:.ctor(...)
LiveKit.MicrophoneSource:.ctor(...)

2. After remote audio subscription:
[LiveKitVoiceChatMgr] Remote audio subscribed (AudioStream playout): <participant>

3. The debugger then stops in:
UnityFramework`ec_tell_frac
In some attempts, the process instead crashes around:

libsystem_pthread.dylib`___chkstk_darwin
Android works with the same server, token flow, room configuration, and application code.

Relevant SDK behavior
LiveKit SDK 2.0.0 includes Editor/IosLinkOrderDiagnostics.cs.

This file documents that linking Unity's audio archive before liblivekit_ffi.a can crash Opus/CELT on iOS. It also strips conflicting CELT object files from:

Libraries/libiPhone-lib.a
However, Unity 6 exports libGameAssembly.a rather than libiPhone-lib.a.

Therefore, the current post-process logic does not appear to process the Unity 6 archive. In our build logs, we do not see the expected CELT stripping log, and the crash still occurs in ec_tell_frac.

Expected behavior
The SDK’s iOS post-process diagnostics/fix should also support Unity 6 exports using libGameAssembly.a, including:

Safe link ordering of liblivekit_ffi.a before the Unity-generated archive.
Detection and removal of conflicting CELT/Opus object files from the applicable Unity-generated archive.
Clear build-log output stating which archive was detected and modified.

Actual behavior
The current fix targets libiPhone-lib.a, which is absent or unused in Unity 6 exports. The resulting iOS application crashes in the CELT/Opus path while Android remains unaffected.

Question
Could the iOS link-order/CELT conflict mitigation be updated to support libGameAssembly.a for Unity 6 / IL2CPP exports? If there is a preferred integration path or a known fix for this configuration, please advise.

[MaxHeimbrock]

Hi,

Thanks for reporting the issue. I have some follow up questions while I look into the issue.

1. Are you using the Unity audio path or our Platform Audio? See more here: https://github.com/livekit/client-sdk-unity#audio
2. Do you have a chance to test the iOS build from an earlier Unity version? Maybe Unity 2022 or Unity 2023?
3. Are you using a custom app or one of our samples?

[DongYeongJeong]

1. We are currently using the Unity audio path.
   For local capture, our custom application creates a MicrophoneSource, so audio is captured through Unity’s Microphone API and sent through RtcAudioSource. Remote audio is played through AudioStream / Unity AudioSource.
   We previously attempted to switch to Platform Audio during investigation, but encountered PlatformAudio.StartRecording() failing with init_recording failed. The ec_tell_frac crash reports in this issue are from the current Unity audio path.
2. We have not tested an earlier Unity version yet. This project was created with Unity 6.5 (6000.5.x), so we do not currently have a Unity 2022 or Unity 2023 build available for comparison.
3. We are using a custom application, not one of the LiveKit samples.

[MaxHeimbrock]

Thanks for the info.

One last question, can you try the Meet sample app project to repro? This is what I will try today as well for repro of your issue. In the MeetManager script of the scene, disable platform audio in the inspector to use the Unity audio path. Then install to iOS as usual.

I will first try with Unity 2022.3.62f1 and Unity 6000.3.10f1 and then also get Unity 6000.5.x.

[MaxHeimbrock]

I was able to repro on the Meet sample and provide the fix that works for me.

In Unity 6.5 they changed the iOS build process a bit. Can you give the build scripts from this PR a try to confirm it also fixes your builds?
#360

[DongYeongJeong]

I applied the build scripts from PR #360 to our Unity 6000.5.5f1 project and rebuilt the iOS application.
The iOS build and on-device test completed successfully. The previous runtime crash was no longer reproduced during the tested LiveKit connection and audio flow.
Thank you for the fix.