Small unlabeled object
A small meteoroid - possibly unknown, given that it's not circled - tracking right to left, just to the upper-left of center.
It's quite clear, compared to the 'fuzzier' stars and noise around it. Brightest in frames 1, 2 and 4. If you trace an imaginary line between the center point and the upper left corner, it's about 1/3 of the way along, just to the right of that line.