Research And Implementation Of MPEG-4 Homogeneous Transcoding

With the development of multimedia applications, an increasing number of occasions require video data for interaction among different formats and standards. To realize seamless connection in heterogeneous network between different types of access devices, the transcoding of compressed video stream has become a research hotspot of video communication.Early video transcoding mainly concerned in reducing bit-rate to meet the bandwidth requirements of transmission channel. Nowadays, mobile video applications are being widely used. For the limited display size of terminal equipments and limited power resources, frame rate transcoding and image resolution transcoding has become the focus of the study also.This paper is based on MPEG-4 standard, mainly focusing on how to achieve high efficient homogeneous transcoding. First of all, we briefly introduce the basic concepts of video transcoding and the MPEG-4 video codec. We study and analyze the performance of cascaded homogeneous transcoding which is to be used as the reference of high efficient homogeneous transcoding. For the bit-rate reduction, we firstly propose the realization methods for I-VOP and P-VOP respectively, and then present a fast decision of inter-frame macroblock on the basis of reusing macroblock mode information and motion vectors. For the resolution reduction, we propose different methods for 2:1 ratio resolution reduction and arbitrary ratio resolution reduction, including corresponding motion vector synthesis and refinement as well as fast decision of macroblock mode after resolution transformation. For the frame rate reduction, we research some key technologies in detail, such as frame skipping strategy, motion vector reconstruction and refinement, fast decision of macroblock mode, and implement the high efficient frame rate reduction transcoding.Compared with the cascaded transcoding and under the same transcoding configuration parameters, the experimental results show that the high efficient transcoding can significantly reduce the computing complexity and restore the good quality of video, and can be used in the actual video transcoding system.