The camshaft has two seperate cam lobes for every valve. So when reversing the engine the camshaft can slide back and forward, changing wich of the two cam lobes operates the valve. When doing this the running direction of the engine changes. This "sliding camshaft" is operated by hydraulic pressure and air pressure.
Normally this engine has closed valve covers, in the video they are open for inspection after some engine repairs. The older versions of this type of engine have "open cylinderheads" this means there is no valve cover.
