more precise Image timestamp from video after HERO8 Black

[fushi219]

Hi Steffen:
Sorry for my delayed action on GoPro max's calibration mr because of my busy work.

I think there is a better way to calculate each frame's timestamp than the method used below:

OpenImuCameraCalibrator/python/extract_for_kalibr_bagcreator.py

Line 20 in 080cf97

timestamp_ns = cap.get(cv2.CAP_PROP_POS_MSEC) * 1e-3

For cameras after Hero fusion, we can use the STMP in streams to calculate measure's precise timestamp. I have tested the imu's stamps calculated by STMP and gpmf-telemetry in your project, they are almost the same.

As you can see in this issue: gopro/gpmf-parser#160, for cameras after HERO8 Black (v2.5), we can use STMP in CORI streams to calculate more precise frame timestamp.(STMP in CORI does not start from 0.)

[urbste]

Hi fushi219. Thanks for that hint! I incorporated the precise timestamps for GoPro calibration.