The video illustrates how quickly situations can develop. I think some travellers expect that if anything does go wrong and they actually need to know it, the cabin crew will repeat the safety briefing. There isn't always time for that.

I was mildly impressed that the cameraman looked for, and found, the life jacket in the front pocket. I was expecting it to be under the seat. Mind you, the last time I flew I couldn't find it there and nearly got annoyed; checking the safety sheet it turned out to be stored in an overhead cubby-hole. So that's three places it can be. It's definitely worth finding out where it is in advance, and then checking that it's actually there. I suspect, if a previous passenger took it as a souvenir, it might be a while before the plane maintenance noticed it was missing.