Glossary
Cross-stream sync error
The timing offset between simultaneously captured streams like video, depth and IMU.
Definition
Cross-stream sync error is the residual timing offset between streams that are meant to be simultaneous — RGB, depth, IMU and pose. Measured in milliseconds, it determines whether a hand position at time t actually lines up with the depth and image at time t.
01
Why it matters
If depth lags video by tens of milliseconds during a fast reach, the supervision is wrong exactly when the motion is interesting. Sub-frame sync is what makes multi-stream egocentric data trainable rather than merely co-recorded.
02
How Firsthand handles it
Firsthand hardware-triggers every stream onto one PTP clock domain and measures the residual: median 1.12 ms, p99 1.94 ms, with a 2.0 ms ceiling; any episode breaching it is rejected.
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