Nowadays, Dynamic Adaptive Streaming over HTTP (DASH) has become very popular in streaming multimedia contents. In order to offer better user experience and cope with dynamically varying network conditions, a big challenge is to estimate precisely next segment bandwidth, which is a significant premise in determining next multimedia bitrate, especially when multiple clients share the same bottleneck link. In this paper, we address an innovative mechanism to estimate the bandwidth based on MACD indicator and its two thresholds. Then, with the estimated bandwidth, we use GA to determine the next multimedia bitrate. Our simulation demonstrates that our proposed approach outperforms other existing schemes.