We present time resolved measurements of the laser induced plasma development in air. A Q-switched Nd:YAG laser is employed as the excitation source. The detection part of the acquisition system is based on a streak camera. We propose streak image processing technique based on a set of simple algorithms as a way to obtain estimations of plasma core and plasma plume instantaneous velocity. Using of the proposed technique enables us to obtain all data relevant for temporal analysis by a single shot excitation.