Possible Missing Reinitialization After Face Tracking Data Stalls

[Kushyameln01]

While using the VIVE Facial Tracker for extended periods, I occasionally encountered a state where tracking stopped working and could only be restored by reconnecting the DisplayPort / VIVE Streaming connection.

This made me question why the Face Tracking subsystem itself was not recovering automatically, so I reviewed the implementation of the official ViveStreamingFaceTrackingModule.

After valid Eye or Lip data is received once, the module sets:

EyeTrackerInited = true
LipTrackerInited = true

However, if Face Tracking callbacks later stop arriving while the HMD itself remains connected to VIVE Streaming, there does not appear to be a watchdog that checks how long it has been since the last valid Eye or Lip packet was received.

This could result in the following state:

Eye / Lip data received successfully
↓
TrackerInited = true
↓
Face Tracking callbacks stop
↓
HMD remains connected
↓
TrackerInited remains true
↓
No reinitialization is triggered
↓
Face Tracking remains stalled

When the Streaming connection itself is disconnected, StopFaceTracking() resets the tracker state, and VS_StartFaceTracking() is called again after reconnecting.

This behavior appears consistent with the observed case where Face Tracking only recovers after the DisplayPort / VIVE Streaming connection is re-established.

A possible improvement would be to store the timestamp of the most recent Eye and Lip packets and add a watchdog that automatically performs:

VS_StopFaceTracking()
↓
Reset tracker state
↓
VS_StartFaceTracking()

if no valid Face Tracking data has been received for a defined timeout period.

This may allow the Face Tracking subsystem to recover without requiring the entire HMD or DisplayPort connection to be reconnected.