Rate 1 vs. quality is a crucial trade off not only for efficient video coding and transmission but also for adaptive transmission strategies in wireless networks and/or congestionprone networks. Scalable coders are well suited to tackle the time-varying capacities of these environments. In this paper we propose a semi-analytical model suitable for the medium grain scalable option of the H.264 standard and discuss the parameters influencing its performance. Results show it can effectively be used to represent the expected rate for different quality layers and thus its applicability to algorithms for resource optimization.