An encoding system for converting video data to a media stream based on a given intra-refresh rate includes an encoder for encoding the video data to frames based on the given intra-refresh rate, a decoder for reconstructing the encoded frames, and an evaluation unit for scoring macro blocks (MBs) of a current frame being decoded. A score of an intra-MB is defined as a predetermined value, and a score of an inter-MB is generated based on the scores of MBs of previous frames. A controller determines an actual refresh period based on a qualified frame identified based on the scores of the MBs of at least the current frame, and adjusts the given intra-refresh rate based on the actual refresh period.