It sounds like a blown exhaust gasket. It is easy to check before you do something expensive. Start it up and before it gets hot feel around the header to exhaust joint and the header to head gasket. Even at idle you should feel a slight puffing from the leak. Now you probably will not be able to get your hands everywhere so this is where your rubber hose comes into play. Do not stick the rubber hose in your ear or up your nose(welcome back cotter) but close. You should hear the sound when the rubber hose encounters the leak. The leak can be quite small so make sure you go all the way around the joints. If no leaks are found there, check further down the exhaust pipe.
From the video, it does not sound like a rod knock(actual rpm) as opposed to valve related(1/2 rpm). Yes exhaust leaks are 1/2 rpm.
Good luck