Weird bug that I don't understand

While playing any video, I open an other program like gpu-z, cpu-z and video starts to lag for a second whereas it does not occur in windows media player. Anyone can have a idea for this situation ? Thanks.

Such monitoring applications frequently query the processors for information. This can interfere with timing sensitive applications such video playback. The behavior you experience probably varies depending on which video renderer is used by MPC-HC.