As a contribution to the design of an objective quality metric in the specific context of High Definition Television (HDTV), this paper proposes a video quality evaluation model. A spatio-temporal segmentation of sequences provide features used with the bitrate to predict the subjective evaluation of the H.264-distorted sequences. In addition, subjective tests have been conducted to provide the mean observer's quality appreciation and assess the model against reality. Existing video quality algorithms have been compared to our model. They are outperformed on every performance criterion.