Videos compressed using modern compression techniques, such as HEVC, typically have the property of unequal importance. When a video with intra and inter coded frames is transmitted through a network, its different frames can suffer from quality degradation depending on their sizes and channel coding schemes. Moreover, errors in a reference frame can propagate forward and backward over several frames, while errors in a non-reference frame are localized within the same frame. In this paper, we design a system that dynamically determines the coding parameters of layer-aligned multipriority rateless codes depending on the video content and channel condition. For this purpose, we estimate the strength of error propagation and develop a model to estimate quality degradation of a transmitted video accurately. Through minimizing quality degradation, we are able to calculate optimal parameters for the system.