Research And Optimization On Video Codec Of Mobile Videophone

With the arrival of 3G, the bandwidth of wireless network will be significantly increased. 3G may bring boundless opportunities for mobile application. At present, the multimedia related applications, such as mobile TV, mobile videophone, MMS and so on, occupy the majority of the mobile applications. As the greater amount of video data, the 2.5G network can't bear such real-time video data transmission. However, with the development of 3G and its high bandwidth, the mobile videophone application will become more and more popular.This paper focuses on the optimization for mobile video codec, because of the limitation of mobile device performance and the its "mobile" characteristics. The optimization work mainly contains the improvement of motion estimation algorithm, the replacement of Float DCT to Integer DCT and a new method of color space conversion.MPEG-4 is a high-performance video compression standard, which is based on DPCM/DCT model. It includes motion estimation and compensation, FDCT/IDCT, quantization and entropy coding. It is necessary to do some optimizations for the algorithm of motion estimation, because more than 70% coding time is spent by full search motion estimation model. At present, many algorithms for fast motion estimation are proposed, such as TSS, DS, etc. TSS is suitable for strong motion for its long step of first searching. DS is suitable for small motion for its accurate searching. Combination of these two algorithms will produce better results for mobile videophone.Float DCT costs large amount of computing power because of a lot of float operations and multiplications. We can use Integer DCT to replace Float DCT to reduce a lot of coding time. Integer DCT only contains 45 add and 18 shift operations without multiplications. Integer DCT not only improves coding speed, but also ensures the video quality not been decreased significantly.In addition, we suggest a new method to convert image from YUV4:2:0 to RGB565. We use a look-up table to convert image format instead of implementation of converting directly. It really saves a lot of decoding time.