A guided search method for real time transcoding a MPEG2 P frame into H.263 P frame in a compressed domain

Abstract

Our objective is to enable a format transcoding between a heterogeneous compression format in real time mode and to enhance the compression ratio using characteristics of the compression frame. In this paper, we tried to transcode MPEG 2 digital contents having a low compression ratio into H.263 contents with a high compression ratio. After analyzing MPEG2 bit stream and H.263 bit stream of the same original video, we found that the number of intra coded macro blocks in MPEG2 data is much higher that the number of the intra coded blocks in H.263 data. In the process of P frame generation, an intra coded block is generated when a motion estimation value representing the similarity between the previous frame and the current frame does not meet a threshold. Especially the intra coded macro block has a great impact on the compression ratio. Hence we tried to minimize the number of intra coded macro blocks in transcoding the INTRA coded block into INTER coded block using the information about motion vectors surrounding the intra macro block in order to minimize the complexity of the motion estimation process. The experimental results show that the transcoding of MPEG2 into H.263 can be done in real time successfully.