fix Android PlatformAudio

[xianshijing-lk]

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PR description

⏺ Android PlatformAudio: Problems & Solutions

Problem 1: ADM Creation Failed

Symptom:
CreateAudioDeviceModule returned nullptr
Failed to initialize PlatformAudio

Root Cause:
WebRTC's CreateAndroidAudioDeviceModule internally calls GetAppContext() to get the Android application context. But GetAppContext() returns null unless ContextUtils.initialize(context) was called first.

CreateAndroidAudioDeviceModule()
└── GetAppContext()
└── Returns null ❌ (ContextUtils not initialized)

Solution:
Pass the Android Context from Unity to Rust, then call ContextUtils.initialize(context) before any WebRTC audio initialization.

Unity Rust/C++
───── ────────
GetApplicationContext() ──────► livekit_ffi_initialize_android_context()
│
├── do_android_init(vm) // JVM init
└── ContextUtils.initialize(context) // Now GetAppContext() works!

Files changed:

• livekit-ffi/src/cabi.rs - Added livekit_ffi_initialize_android_context()
• webrtc-sys/src/android.cpp - Added init_android_context()
• client-sdk-unity/.../FFIClient.cs - Calls the init with context
• client-sdk-unity/.../NativeMethods.cs - P/Invoke declaration

---

Problem 2: Wrong ADM Factory Function

Symptom:
AdmProxy: All Android audio layers failed!

Root Cause:
The code was using the generic CreateAudioDeviceModule() which doesn't work properly on Android. Android requires CreateAndroidAudioDeviceModule() from the Android-specific header.

Solution:
Changed adm_proxy.cpp to use the correct function:

// Before (wrong):
#include "modules/audio_device/include/audio_device.h"
platform_adm_ = webrtc::AudioDeviceModule::Create(...);

// After (correct):
#include "sdk/android/native_api/audio_device_module/audio_device_android.h"
platform_adm_ = webrtc::CreateAndroidAudioDeviceModule(...);

File changed:

• webrtc-sys/src/adm_proxy.cpp

---

Problem 3: Empty GUID Validation Failed

Symptom:
Recording device at index 0 has no GUID

Root Cause:
Unity SDK threw an exception when device GUID was empty. But on Android, devices don't have GUIDs - WebRTC returns empty strings.

Solution:
Allow empty GUIDs and pass them to native code, which falls back to index 0:

// Before:
if (string.IsNullOrEmpty(deviceId))
throw new InvalidOperationException("has no GUID");

// After:
SetRecordingDevice(deviceId ?? ""); // Empty string triggers fallback

File changed:

• client-sdk-unity/.../PlatformAudio.cs

---

Problem 4: Device Not Found with Empty GUID

Symptom:
Failed to set recording device: Device not found

Root Cause:
Native code searched for a device matching the empty GUID string, found nothing.

Solution:
Added fallback in C++ - if GUID is empty and devices exist, use index 0:

bool AudioDeviceController::set_recording_device_by_guid(rust::String guid) const {
int16_t count = adm_proxy_->RecordingDevices();

  // Android fallback: empty GUID → use index 0
  if (guid.empty() && count > 0) {
      return adm_proxy_->SetRecordingDevice(0) == 0;
  }
  // ... normal GUID lookup for desktop

}

File changed:

• webrtc-sys/src/audio_device_controller.cpp

Breaking changes

N/A

MSRV

N/A

Testing

Tested with Unity

Async

N/A

[github-actions]

Changeset

The following package versions will be affected by this PR:

Package	Bump
libwebrtc	patch
livekit	patch
livekit-ffi	minor
webrtc-sys	patch