压缩域MPEG-2视频流无缝拼接中的码率控制算法

Rate Control Algorithm in Compressed Domain Seamless Splicing MPEG-2 Video Streams

为防止由视频流无缝拼接造成的解码缓冲器溢出问题,结合TM5码率控制算法和拼接过程中已解码图像的信息,提出了一种有效的码率控制算法.该算法首先通过计算待拼接视频流中的vd(vbv-delay)值来求取拼接期的目标比特数,然后根据图像原来的量化参数估计宏块的空间活动性,最后利用已解码图像中的比特数分布情况来指导虚拟缓冲器充溢度的调整.实验结果表明:该算法能非常有效地实现无缝拼接,且拼接后视频流的vd值与新视频流的vd值非常吻合,并能有效保证图像的降质在允许的范围之内.

In order to prevent the decoder buffer underflow in video stream seamless splicing, this paper proposes an efficient rate control algorithm, which adapts the TM5 rate control strategy by the information extracted from decoded picture. This algorithm educes the target bit number of the splicing period from the VBV-delay of the bit streams to be spliced, estimates the spatial activity of macro blocks by the former quantization factor, and adjusts the virtual buffer according to the bit number distribution of the decoded pictures. The experimental results show that this algorithm can splice the bit streams seamlessly, the VBV-delay value of the spliced bit stream is coincident with that of the new bit stream, and the loss of picture quality is controlled within the accepted tolerance.