Here's my uninformed speculation.
Looks like there's a life raft in the H20, plus the nearby ship looks like Russian CG. So, they're either rescuing, or practicing rescues. The Helo looks like it has some form of pontoons which might allow limited water landing capability like the Sikorsky something-or-other the USCG used.
Hard to tell from the vid, but the tailrotor starts acting funny on initial takeoff, like it was losing power. Maybe it's just the stroboscopic effect, but looks like something went wrong. Then, on the final attempt, you can see the rotor cone pointing forward, as if he was attempting a normal takeoff. Maybe the ship was too heavy for a vertical departure? Once that rotor cone got pointed too far towards the waves it was game over -- boy do those choppers come apart in a hurry!!!!!