This document covers how to record data from multiple primary-secondary synchronized devices.

Prerequisites

• Synchronize Multiple Devices

External Sync Constraints

First, connect the master and subordinate devices according to the product multi-device sync documentation.

• All master and subordinate devices must use the same camera configuration (fps and resolution).
• All master and subordinate devices must run the same device firmware (Update Device Firmware).
• It is recommended to start all subordinate devices first, then the master device.
• The same exposure values should be set on all devices.
• The “Subordinate Delay Off Master” is set per subordinate device relative to the master.

Recording with Each Device on Separate Host PC

In the following example, each device has its own dedicated host PC. We recommend dedicating devices to PCs to avoid USB bandwidth and CPU/GPU usage issues.

Subordinate-1

1. Set up recorder on first unit

k4arecorder.exe --external-sync sub -e -8 -r 5 -l 10 sub1.mkv

2. Device starts waiting

Console:

Device serial number: 000011590212
Device version: Rel; C: 1.5.78; D: 1.5.60[6109.6109]; A: 1.5.13
Device started
[subordinate mode] Waiting for signal from master

Subordinate-2

1. Set up recorder on second unit

k4arecorder.exe --external-sync sub -e -8 -r 5 -l 10 sub2.mkv

2. Device starts waiting

Console:

Device serial number: 000011590212
Device version: Rel; C: 1.5.78; D: 1.5.60[6109.6109]; A: 1.5.13
Device started
[subordinate mode] Waiting for signal from master

Master

1. Start recording on master device

>k4arecorder.exe --external-sync master -e -8 -r 5 -l 10 master.mkv

2. Wait for recording to complete

Recording with Multiple Devices Connected to Single Host PC

Multiple Femto Bolts can be connected to a single host PC. However, this may require high USB bandwidth and host compute requirements. To reduce demands:

• Connect each device to its own USB host controller
• Use a powerful GPU that can handle the depth engine for each device
• Only record required sensors and use lower frame rates
• Always start subordinate devices first, master device last

Subordinate-1

1. Start recorder on subordinate device

>k4arecorder.exe –device 1 –external-sync subordinate –imu OFF -e -8 -r 5 -l 5 output-2.mkv

2. Device enters waiting state

Master

1. Start master device

>k4arecorder.exe --device 0 --external-sync master --imu OFF -e -8 -r 5 -l 5 output-1.mkv

2. Wait for recording to complete

Playing Back Recordings

Use 《K4A Viewer for Femto Bolt》 to play back recordings.

Tips

• Record with manual exposure on synchronized cameras. RGB camera auto exposure can affect timing sync.
• Restarting a subordinate device will lose sync.
• Some 《Hardware Specifications》have max 15 fps support. We recommend not mixing modes/frame rates between devices.
• Connecting multiple units to a single PC can easily saturate USB bandwidth, consider dedicating host PCs per device. Also be mindful of CPU/GPU compute.
• Disable IMU if not needed to improve reliability.

See 《Known Issues and Troubleshooting for Femto Bolt》for any issues.

Also see

• 《Synchronize Multiple Devices》
•  《K4A Recorder for Femto Bolt》and other info.
• 《K4A Viewer for Femto Bolt》or configure RGB camera attributes not available via recorder.
• Update Device Firmware.
• Let me know if you need any clarification or have feedback on the translation!