orbbec
Crash in k4abt_tracker_destroy when using dual Orbbec Femto Mega with Azure Kinect Body Tracking (Access Violation 0xC0000005)
Describe the bug When using two Orbbec Femto Mega cameras with Azure Kinect Body Tracking SDK (k4abt) inside Unity, the application randomly crashes with:
0xC0000005 Access Violation
The native call stack always points to:
k4abt_tracker_destroy
or other internal functions inside k4abt.dll. The crash is non-deterministic, sometimes happening immediately on startup, sometimes after minutes, sometimes after hours.
This makes Azure Kinect Body Tracking unstable and unusable in dual-camera setups.
Reproduction Steps
Connect two Orbbec Femto Mega cameras using Sync Hub.
Run Unity application using:
Orbbec SDK
Azure Kinect Body Tracking SDK (k4abt)
Azure Kinect Sensor SDK
LightBuzz.Kinect4Azure plugin (wrapper for k4abt)
Start depth streaming on both devices.
Initialize k4abt tracker.
Run body tracking loop.
Wait until application crashes (sometimes instant, sometimes after minutes/hours).
Crash occurs regardless of:
DirectML mode
CPU mode
Unity project size (even minimal scenes crash)
Expected behavior The application should run body tracking stably with two synchronized Femto Mega cameras without crashing inside k4abt’s internal cleanup/destruction routines.
Log Output
Right before the crash (with custom debug DLL):
[LIGHTBUZZ] Created IMU frame source. [LIGHTBUZZ] Created floor frame source. [LIGHTBUZZ] Popped body tracking result.
Immediately followed by native crash:
0x00007FFE67A97918 (k4abt) k4abt_tracker_destroy 0x00007FFE67A830C9 (k4abt) k4abt_tracker_destroy ... 0xC0000005 Access Violation
Crash dump consistently identifies k4abt_tracker_destroy as the failure point.
I can provide:
crash.dmp
Player.log
DxDiag
Plugin folder (Orbbec DLL + Microsoft DLL + LightBuzz debug DLL)
System Environment:
OS: Windows 11
Architecture: x86_64
GPU: NVIDIA RTX 5080 (Studio Driver 581.57)
Unity: Unity 6 (Windows x64 Player)
Visual Studio: 2022 (v17.x)
Tool/SDK Version:
Orbbec SDK: Latest available (2025)
Azure Kinect Body Tracking SDK (k4abt): Azure Kinect BT 1.1.2
Azure Kinect Sensor SDK: 1.4.2
LightBuzz.Kinect4Azure Plugin: Custom debug build (2025/11)
Device Information:
Model: Orbbec Femto Mega × 2
Firmware Version: Latest 2025 firmware provided by Orbbec
Connection: Via Orbbec Sync Hub, Standalone Mode
Additional context
The crash only happens when two Femto Mega devices are used.
Single-camera body tracking never crashes.
Crash behavior matches a known Orbbec report: https://github.com/orbbec/OrbbecSDK/issues/183
We suspect a thread synchronization issue inside k4abt when frames are briefly dropped by one camera during Sync Hub operation.
Both Orbbec and LightBuzz engineers suggested the root cause lies in the Azure Kinect Body Tracking internal runtime.
We are happy to provide any additional logs or to run specific diagnostic builds.
Sorry, I don’t have a good solution either. The Azure Kinect Body Tracking library is not open source. On Microsoft’s AKDK GitHub, others have reported similar issues, but they remain unresolved.
