Visual discomfort/fatigue problems in 3D video have become an important issue. In this paper, we examine the factors that affect human perception of depth and visual comfort from stereoscopic video. For this, we conduct subjective quality assessments from which we extract four factors - temporal variance, disparity variation in intra-frames, disparity variation in inter-frames and disparity distribution of frame boundary areas. Based on these four factors, we design a no-reference stereoscopic video quality perception model (SV-QPM) as an objective quality assessment metric for stereoscopic video. The proposed SV-QPM does not require depth map but utilize the disparity information by simple estimation, and the model parameters are estimated based on linear regression. The experimental results show that our proposed model exhibits high consistency with subjective quality assessment results in terms of a Pearson correlation coefficient value of 0.808, and the prediction performance exhibits good consistency with zero outlier ratio value.