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record-external-synchronized-units.md

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title description author ms.author ms.reviewer ms.prod ms.date ms.topic keywords
Use Azure Kinect recorder with external synchronized devices
Learn how to record data from devices configured for external synchronization using the Azure Kinect Recorder.
tesych
tesych
jawirth
kinect-dk
06/26/2019
conceptual
Kinect, sensor, viewer, external sync, phase delay, depth, RGB, camera, audio cable, recorder

Use Azure Kinect recorder with external synchronized devices

This article provides guidance on how the Azure Kinect Recorder can record data from external-synchronization configured devices.

Prerequisites

External synchronization constraints

  • Master device can't have SYNC IN cable connected.
  • Master device must stream RGB camera to enable synchronization.
  • All units must use the same camera configuration (framerate and resolution).
  • All units must run the same device firmware (update firmware instructions).
  • All subordinate devices must be started before the master device.
  • The same exposure value should be set on all devices.
  • Each subordinate's Delay off master setting is relative to the master device.

Record when each unit has a host PC

In the example below, each device has its own dedicated host PC. It's recommended you connect devices to dedicated PCs to prevent issues with USB bandwidth and CPU/GPU usage.

Subordinate-1

  1. Set up recorder for the first unit

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

  2. Device starts waiting

    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 for the second unit

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

  2. Device starts waiting

    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

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

  2. Wait until recording finished

Recording when multiple units connected to single host PC

You can have multiple Azure Kinect DKs connected to a single host PC. However, that can be very demanding to USB bandwidth and host compute. To reduce the demand:

  • Connect each device into own USB host controller.
  • Have a powerful GPU that can handle depth engine for each device.
  • Record only needed sensors and use lower framerate.

Always start subordinate devices first and the master last.

Subordinate-1

  1. Start recorder on subordinate

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

  2. The device goes into 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 recording to finish

Playing recording

You can use the Azure Kinect viewer to play back recording.

Tips

  • Use manual exposure for recording synchronized cameras. RGB camera auto-exposure may impact time-synchronization.
  • Restarting subordinate device will cause synchronization to be lost.
  • Some camera modes support 15 fps max. We recommended that you don't mix modes/frame rates between devices
  • Connecting multiple units to single PC can easily saturate USB bandwidth, consider using separate host PC per device. Pay attention to CPU/GPU compute as well.
  • Disable the microphone and IMU if they aren't needed to improve reliability.

For any issues see Troubleshooting

See also