I think I have seen that footage on many WWI documentaries.
AFAICR it was from early in the war, the ship is already sideways and hundreds of sailors are clinging and standing over the side of the hull, in a very calm sea.
Suddenly, the ships turns completely upside down in an instant, and hundreds of sailors are tossed around like the fake snow in a snow-globe, what was that ship? Was anyone rescued? And, can anyone find that footage on the web?
Wow, good find Slithy Tove! As the comments at YouTube point out, there are several frames removed that are the most disturbing ones of the sailors being tossed around.
The good news was that it was sunk not in the north Atlantic, were it could have meant a quick death in freezing waters, but in the warmer waters of the Mediterranean. Thanks to their training, out of 1,087 men only 89 died. Still, it is puzzling why it seems that the order to abandon ship was given too late.