It's a bit hard to tell from the video due to the wind noise, but my first thoughts are that maybe the drivechain is overtightened? Basically check the slack with someone sitting on the bike, move the bike so the wheels rotate 1/4 turn check again, rotate another 1/4 turn check again, etc until the wheels have rotated one full turn.
Also check chain for tight sections. Jack bike & spin back wheel.
Bob
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Remember that Assumption is the mother of all f**k-ups.
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