I am not a mechanic but the knocking sound appears to be coming from the front of the engine and might be cam drive related. The timing chain and/or gear could be worn to the point where there is sufficient backlash. Large amounts of backlash will cause a knocking sound at idle rotational speeds which sometimes sounds similar to a worn connecting rod wrist pin. Once the engine speed is increased the sound disappears. Maybe someone on this forum has a method for checking this possibility.