During the last few years, different parametric models were proposed for video quality estimation. Each model uses different parameters as inputs, such as bit rate, frame rate and percentage of packet loss, and each model was designed and tested by their authors for a particular codec, display resolution and/or application. This paper presents a review of the parametric models published by ten different groups of authors. Each model is briefly described, and the relevant parametric formulas are presented. The performance of each model is evaluated and contrasted to the other models, using a common video clips set, in different coding and transmission scenarios. Based on the results, a new and more general parametric model is presented, which takes into account bit rate, frame rate, display resolution, video content and the percentage of packet loss.