| Summary: | 碩士 === 國立臺北大學 === 通訊工程研究所 === 95 === Transmitting the high quality multimedia data in wireless networks has become a tendency in recent years. The emerging video coding standard, H.264/AVC, has much better coding efficiency than prior standards, such as MPEG2, MPEG4 and H.263++. At the same time, it can provide the fine quality of image. So it exactly meets the present needs. In the application of H.264, one of the challenges in wireless communication is how to reduce the probability of error to keep the quality of the image. Therefore, we have to join suitable error resilience features to reduce that the quality degradation of the image due to the errors. And the intra block refresh is an efficient tool to resist errors. Besides, the other problem is the bit rate control. Due to the various types of image and the complicated encoding procedure make fluctuations in bit rate. It makes for difficulty in the allocation of bandwidth and transmission delay. Then frames cannot be played smoothly. Previous rate control methods were inaccurate in H.264. Besides, to apply resilience features in the encoder would affect both the characteristic of input image and encoding system. For this reason, it’s necessary to develop a new method for rate control. This work proposes a method of rate control applying to H.264 with intra macro-block refresh. This method utilizes the close relation between the rate and the number of zero coefficients after being transformed and quantized, ρ. And ρ is one to one mapping to quantization parameter. So the R-ρmodel was built. The target rate is substituted for the R-ρmodel before MBs are encoded. And we can obtain a QP. After that, we considered the characteristic of intra macro-blocks adjusting those parameters instantaneously while the encoder is encoding the MBs. Such can control the rate more effectively and keep the image quality simultaneously.
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