[Question] Sensor Phase Determinism, VBI & Rolling Shutter Specs (Hero 12)

[DrordeHartog]

Context: I am an engineering student developing a multi-camera swimming analysis system. We are using Hero 12 units to model high-speed kinematics (120fps) where we require <1ms temporal precision.
The Goal:We are implementing a software-based synchronization method using short-duration flashes to measure the random Phase Shift between independent camera oscillators. To finalize the architecture, we need to validate specific firmware behaviors regarding sensor readout timing.
Questions

1. Boot-to-VSYNC Determinism: I f we power on two Hero 12s simultaneously via USB-C injection, is the time duration from Boot to the first Sensor VSYNC deterministic (constant cycle count)? Or does it vary significantly due to OS loading tasks? (e.g., is the variance ±5ms or >±100ms?)
2. Phase Reset on Record: When the "Start Record" command is received (via Bluetooth Remote), does the sensor perform a hard reset of the vertical readout phase (restart scanning from Row 0 immediately), or does it simply latch onto the next available frame from the free-running oscillator?
3. Rolling Shutter Correction (RSC) / BERS: We intend to use the rolling shutter distortion as a velocity measurement tool. Does the Hero 12 support the BERS=1 command via QR to fully disable digital rolling shutter correction, ensuring we get raw geometric distortion?
4. Vertical Blanking (VBI): What is the specific Vertical Blanking Row count ($R_1$) for the 8:7 and 16:9 modes at 120fps? We need this to calculate the exact row-to-time ratio ($t_{readout}$ vs $t_{total}$).
5. Scan Direction: Is the sensor scan direction fixed (Top-to-Bottom) regardless of the camera's physical orientation (accelerometer data)? If we mount the camera upside down, does the readout direction flip?

Technical Details

• Model: GoPro Hero 12 Black
• Firmware: Latest Stock
• Use Case: Biomechanics / Photogrammetry