Video frame messages correlate the frames of a video recorded by a camera with the time of the activity.
Moment the message refers to, in UTC. FIT stores it as seconds since the FIT epoch (December 31, 1989, 00:00:00 UTC); decoders usually expose it as a regular date.
Millisecond part of the timestamp, for sub-second precision.
frameNumberUint32Number of the frame shown at the timestamp.
mesgNumStringGlobal message number identifying the kind of message. Decoders use it to know which profile to apply to the data.