When comparing the performance of different video coding approaches, improvements or new codec designs, one of the most important performance metrics is the Rate/Distortion (R/D), where distortion use to be measured in terms of PSNR (Peak Signal-to- Noise Ratio) values. However, it is well known that this metric not always capture the distortion perceived by the human being. So, a lot efforts were performed to define an objective video quality metric that is able to measure video quality distortion close to the one perceived for the destination user. In this work, we perform a study of different available objective quality metrics in order to evaluate their behaviour, taking as reference the classical PSNR metric. Our purpose is to find, if any, a video quality metric that is able to substitute PSNR for video quality assessment and determine a more accurate R/D performance metric when designing and evaluating video codec proposals.