Synchronize Multiple Camera

[zhoujun-7]

Hi, Etienne!

Thank you for this helpful python wrapper. The code is clear with single camera. But there is not example for multiple camera. Could you please kindly give a example to synchronize multiple cameras using "wired_sync_mode"?

Thanks
Jun

[shagren]

Subordinates:

 config1 = Config(..., wired_sync_mode=WiredSyncMode.MASTER)
 config2 = Config(..., wired_sync_mode=WiredSyncMode.SUBORDINATE, subordinate_delay_off_master_usec=200)
 config3 = Config(..., wired_sync_mode=WiredSyncMode.SUBORDINATE, subordinate_delay_off_master_usec=400)
 ....
 device1=PyK4A(config=config, device_id=device_id)
 device1.start()
 device2.start()
...
while True:
   capture1 = device1.get_capture()
   capture2 = device2.get_capture()
   ...

Each subordinate must have own subordinate_delay_off_master_usec. I do not remember exact value, but each next must be greater by some minimal value. 200 is suitable in any case, but you can read SDK docs for better value.

All devices must have same Color and Depth modes, exposure and powerline_frequency settings.

Sometime captures will be returned from different ticks (external trigger ticks). You can compare capture.depth_timestamp_usec with each other, look at https://github.com/microsoft/Azure-Kinect-Sensor-SDK/blob/develop/examples/green_screen/MultiDeviceCapturer.h .

[zhoujun-7]

Hi Shagren,

Thank you for your replying. I had tried your example script. The script includes multiple cameras and works well.
However, with the limited number of USB ports, sometimes it's impossible to put all cameras into a single script. When I separate each camera into a individual script. The time synchronization is failed.

Here are the codes.
Master script:

config1 = Config(..., wired_sync_mode=WiredSyncMode.MASTER)
device1=PyK4A(config=config1, device_id=device_id)
device1.start()
while True:
   capture1 = device1.get_capture()

Subordinate script:

config2 = Config(..., wired_sync_mode=WiredSyncMode.SUBORDINATE, subordinate_delay_off_master_usec=200)
device2=PyK4A(config=config2, device_id=device_id)
device2.start()
while True:
   capture2 = device2.get_capture()

The Subordinate script is launched firstly, then the Master script launched subsequently.

Looking forward your reply!

Thanks,
Jun

[shagren]

@zhoujun-7 , you should counts start_timestamp_offset_usec, see PyK4APlayback.configuration.
Each camera will start with some delay from "start point". This offset contains this delay.

Then MKV frame with timestamp X has "local setup timestamp" equal X + playback.configuration.start_timestamp_offset_usec. Same for both cameras.