As the vanes close, the reduced flow area causes an increase in engine exhaust pressure, this increases the flow energy available to the turbine. The changing angle of the vanes angle influences the efficiency of the turbine.
Nice video but there is one mistake in 1 phase starting at 0:20. The exhaust gas coming from the cylinders hits the turbine and it rotated in the opposite direction from the real.
The fixed blades on the position of maximum blowing position is better instead the variable, and the balance of gas must be placed out of the turbo, in order avoid the increase temperature, Where? fitted on escape colector.See pls my invention of the diesel motor 2 strokes by valves and save the 50% of consumption.