public MixEffectBlock(Switcher switcher, IBMDSwitcherMixEffectBlock bmd, IMediator mediator)
        {
            _switcher = switcher;
            _bmd      = bmd;
            _mediator = mediator;

            _transitionParameters = _bmd.GetTransitionParameters();

            _bmd.AddCallback(new MixEffectBlockCallback(this, _mediator));
            _transitionParameters.AddCallback(new TransitionParametersCallback(_transitionParameters, _mediator));
        }