How do you determine the timestamp of the first frame about gyroflow HOT 4 CLOSED

Every camera is different, but telemetry-parser tries to return t = 0 at the middle of the first frame
Remember that there are many samples per frame, and the negative t is the top row of the first frame, then it goes to 0 in the middle and then positive at the bottom
That's assuming you're using util::normalized_imu() or util::normalized_imu_interpolated()

Gyroflow also takes into account exposure time and some other data depending on camera, for Insta360 it's here:
https://github.com/gyroflow/gyroflow/blob/master/src/core/gyro_source.rs#L390-L414
This is important for the most accurate timing

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Thank you for your explanation.

In the given code snippet, it seems that only Timescalers with t>=0 have been considered.

Can I say that the first non negative Timescaler is the reference timestamp of the first frame, since the interval between two Timescaler is exactly 1/fps.
And the actual timestamp of the first frame is obtained based on the formula in the code snippet.

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It's not that simple, every frame has an additional time offset, based on the exposure time, that offset is calculated in that code snippet I linked.
It also takes into account gyro_timestamp and first_frame_timestamp, but that's already calculated in telemetry-parser

To verify the timestamp per frame, you can Export project file (with processed gyro data) from Gyroflow, and then in that .gyroflow json file, you'll have "synced_imu_timestamps_with_per_frame_offset" field

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Ok, I'll try to use the synced imu timestamp to sync with another imu.

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