Motion Vector Estimation In Video Encoding And Transcoding

With great applications of wireless communication, there are great challenges in the coding and transmission technology of video. Because data quantity of video is very big, fast coding algorithm used must have high data compression ratio and low complexity, and least data quantiy used can transmit most information quantity in order to satisfy video's real time request, when video is transmitted in narrow wireless channel. Motion Estimation is one of key technology in the video image compression coding. Video signals have very high motion correlation in temporal direction, motion estimation and motion compensation technology based on block matching can eliminate redundancy of inter-frame's effectively to achieve high compression ratio. Commonly, motion estimation algorithm consumes about 70% computing time in coder, so to improve the coder's speed, the efficiency of motion estimation must be improved firstly.Furthermore, with Internet and mobile communication's high development, various client devices having different performance appear, such as: cellular phone, PDA, hand-held computer, laptop computer, etc. These client devices hope to gain access to Internet in wireless channel, and browse Internet's content. As Internet and wireless network have different bandwidth, they have different code rate accordingly. If video signal stream compressed is transmitted in wireless channel from Internet to client devices, coded video signal stream will not match the wireless channel. So, proxy need to be set between generic WWW servers and client devices, transcoding video signal stream which has been coded and compressed. Proxy can transform high speed video stream into low speed video stream to make video signal stream transmitted accurately in mobile wireless network, and provides client devices different quality of service.The works we have researched include several aspects as follows:(1) Traditional motion estimation algorithms are analysed, and a fast motion estimation algorithm based on video objects' motion character is proposed. The simulation experiment result shows this algorithm is adapted to image sequences with different motion characteristic, and its performance is close to full search algorithm while greatly reducing computation complexity.(2 ) Various transcoding models in video transcoding are analysed. Video transcoding can be carried out not only in pixel domain but also in transform domain, namely DCT domain. Videotranscoding has three means: code rate conversion, resolution conversion, conversion between coding standard. Code rate conversion commonly is reducing video's code rate. Resolution conversion commonly is reducing video's temporal resolution and spatial resolution. Conversion coding standard is recoding video with another coding standard which has been coded with a standard.(3) In reducing temporal resolution transcoding two motion vector composed methods are analysed: linear interpolation method and FDVS method. A new motion vector composed method is proposed. Experiment results reveal the proposed algorithm is computationally efficient while keeping better image quality compared with the previous presented algorithms.