Sort of like a high-speed glacier.

A patch of fresh water with a lower freezing temperature in a salt water current brought up against the shore perhaps. . ?

I wonder when this happened. It looked like it was shot on VHS.

When things get colder, I wonder if the wall of ice will stop encroaching so politely as it did here.

One guy (taking photos, towards end of the video) is clearly wearing shorts and t-shirt, so the ambient air temperature can't have have been far below room temperature (13C?)... how the hell then did the sea freeze in mid-motion!?

... icesheet moving, thats normal when you have a larger body of water(with currents) covered with ice.
Obviously Newfoundland(shoreline) seeldom freezes.

... pack ice

if this is one of the ways glaciers are formed?

I am from Turk's Cove Newfoundland and I have seen this so often, you people just need to lay back and enjoy the wonder.
Don't let the absence of snow get ya.
It can get cold enough to turn the top layer of salt water to a slushy kinda material you see here.
Now this is a really good example.
I have seen less and much more build up than this.
The secret to getting a good look is...when its cold (that cold there, -15 or so) there is usually no wind. The stuff just lays there and still looks great with teh little swells.
But this time it was cold, they got a wind, and the stuff was driven up on the beach.
Grab a gin and tonic and merry christmas (without an X)