This paper proposes software optimization strategies using a low-cost SoC which include float-point to fix-point conversion scheme based on statistical analysis and performance oriented customizing scheme for on-chip memory's capacity,  and presents optimization methodology based on these strategies for computation intensive applications.  the MPEG-4 AAC decoding in real-time is implemented as a case study to illustrate the efficiency of the proposed optimization strategy in both performance and cost.  The strategy and methodology also can be used to optimize other DSP applications.