<span lang="en">The provision of video streaming services over mobile data accesses is emerging as a promising service for the current and future Internet. This paper focuses on the study of H.264- based video contents over a typical 3G UMTS connectivity. The performance of the service is finally determined by the combined effects of the encoding features and the radio access characteristics. Therefore, based on the UMTS channel modeling, this paper tries to find out the optimal encoding configuration that provides the best service performance, in terms of Quality of Experience. In addition to other well-known encoding parameters, such as the source target bitrate, frame rate or resolution, this paper studies the impact of the maximum video slice size as a critical parameter for the performance of the considered service.</span>